The 2017 Phenomenology Symposium will be held May 8-10, 2017 at the University of Pittsburgh. It will cover the latest topics in particle phenomenology and theory plus related issues in astrophysics and cosmology.
Early registration ended April 16, 2017
Registration closed April 30, 2017
Talk submission ended April 23, 2017
Conference banquet May 9, 2017
Plenary program and full program are now available.
Plenary topics and speakers:
Parallel session mini-reviews:
Forum on career development for graduate students:
May 8, 1:00 - 1:45pm, Speaker/facilitator: Elizabeth Simmons (MSU)
PITT PACC Travel Awards: With support from the NSF and DOE, there are a number of awards (up to $300 each) available to domestic graduate students for travel and accommodation to Pheno 17. A student applicant should send an updated CV and a statement of financial need, and arrange for a short recommendation letter sent from their thesis advisor, by email to pittpacc@pitt.edu with the subject line "Pheno 17 travel assistance". The decision will be based on the academic qualification, the talk submission to Pheno 17, and the financial need. The deadline for the application is April 9, and the winners will be notified by April 17. (Each research group may be limited to one awardee. Winners in the previous years may have lower priority for consideration. Winner institutes and names will be announced at the Symposium banquet.)
PHENO 2017 ORGANIZERS: Brian Batell, Cindy Cercone, Ayres Freitas, Dorival Gonçalves, Tao Han (chair), Ahmed Ismail, Adam Leibovich, David McKeen, Satyanarayan Mukhopadhyay, and Brock Tweedie
PHENO 2017 PROGRAM ADVISORS: Vernon Barger, Lisa Everett, Kaoru Hagiwara, JoAnne Hewett, Arthur Kosowsky, Yao-Yuan Mao, Tilman Plehn, Xerxes Tata, Andrew Zentner, and Dieter Zeppenfeld.
OTHER ANNOUNCEMENTS
MC4BSM will be held at SLAC May 10-12, 2017
BLV2017 will be held at Case Western Reserve University May 15-18, 2017
TeVPA 2017 will be held at Ohio State University August 7-11, 2017
LOCAL EVENTS
The Pittsburgh Pirates play the Milwaukee Brewers at 1:35 PM May 7, 2017
The Pittsburgh Marathon will take place May 7, 2017
Measurements of the inclusive and differential top-quark pair production cross sections in proton-proton collisions with the ATLAS detector at the Large Hadron Collider are presented at center-of-mass energies of 8 TeV and 13 TeV. The inclusive measurements reach high precision and are compared to the best available theoretical calculations. These measurements, including results using boosted tops, probe our understanding of top-pair production in the TeV regime. The results are compared to Monte Carlo generators implementing LO and NLO matrix
elements matched with parton showers and NLO QCD calculations. The production of top-quark pairs in association with W and Z bosons is also presented. The measurement uses events with multiple leptons and in particular probes the coupling between the top quark and the Z boson.
The cross-section measurement of photons produced in association with top-quark pairs is also
discussed. These process are all compared to the best available theoretical calculations.
We investigate various kinematic methods to resolve two fold ambiguities in paring b-quark and lepton in the $t\bar t$-like events at the LHC. We generalize the methods to physics beyond the standard model.
Measurements of single top-quark production in proton proton collisions at the Large Hadron Collider are presented at center-of-mass energies of 8 TeV and 13 TeV. For the t-channel measurement, the single top-quark and anti-top-quark total production cross-sections, their ratio, as well as measurements of the inclusive production cross sections are presented. Differential cross-section measurements of the t-channel process are also discussed. A measurement of the production cross-section of a single top quark in association with a W boson, the second largest single-top production mode, is also presented. Finally, measurements of the properties of the Wtb vertex allow to set limits on anomalous couplings. All measurements are compared to state-of-the-art theoretical calculations.
We propose a new method for measuring the top-quark width based on the on-/off-shell ratio of b-charge asymmetry in pp>Wbj production at the LHC. The charge asymmetry removes virtually all backgrounds and related uncertainties, while remaining systematic and theoretical uncertainties can be taken under control by the ratio of cross sections. Limited only by statistical errors, we find that our approach leads to good precision at high integrated luminosity, at about a few hundred MeV at HL-LHC. This approach directly probes the total width, in such a way that model-dependence can be minimized. It is complementary to existing cross section measurements which always leave a degeneracy between the total rate and the branching ratio, and provides valuable information about the properties of the top quark. The proposal opens up new opportunities for precision top measurements using a b-charge identification algorithm.
to update the newest result of the top mass and property measurement at ATLAS experiment.
Resonances in the ttbar mass spectrum are well-motivated signatures of new physics and can be used to discover or constrain many proposed extensions to the Standard Model. Such models often make further predictions about the nature of these resonances, for example the polarisation of the top quarks. I will present a realistic study of the improvements in sensitivity that can be made when incorporating top polarisation information in the limit setting procedure when compared to only using the mass spectrum in both the semi-leptonic and di-leptonic ttbar channels, using a Randall-Sundrum model often used for presenting results by ATLAS and CMS as a benchmark. I will show these improvements are particularly important for wide resonances and the di-leptonic channel.
Any particle that is charged under $SU(3)_C$ and $U(1)_{EM}$ can mediate the $gg \rightarrow \gamma\gamma$ process through loops. Near the threshold for the particle pair production, gauge boson exchanges necessitate the resummation of ladder diagrams. We discuss the leading log order matching of the one-loop result with non-relativistic effective theory resummed result. We show how the diphoton invariant mass spectrum varies depending on decay width, color representation and electric charge of the particle. The exclusion limits on the product of $SU(3)_C$ and $U(1)_{EM}$ charges of the new scalar or fermion particle are obtained from current LHC data. In addition, we apply the same method to the top quark to discuss its observation and mass measurement in the diphoton channel in hadron colliders.
We present a search for new massive particles decaying to heavy-flavour quarks with the CMS detector at the LHC. The prominent signature is the resonant production of top quark pairs. Decay channels to vector-like top partner quarks, such as T', are also considered for the first time. We use proton-proton collision data recorded at a centre-of-mass energy of 13 TeV. The search is performed in both hadronic and semileptonic decay channels of the top quark or of the top-partners. Due to the high momentum range in which these objects are produced, specific reconstruction algorithm and selections are employed to address the identification of these boosted signatures.The results are presented in terms of upper limits on the model cross section.
Observations show that galaxies have magnetic fields with a component that is coherent over a large fraction of the galaxy with field strengths of order microGauss. These fields are supposed to be the result of the amplification of initial weak seed magnetic fields of unknown nature. There are two scenarios for their origin under current discussion: a bottom-up (astrophysical) one, where the needed seed field is generated on smaller scales and, a top-down (cosmological) scenario where the seed field is generated prior to galaxy formation in the early universe on scales that are large now. In our present study we assume that seed magnetic fields have been generated in the early universe. We show that these seed fields lead to primordial magnetohydrodynamical (MHD) turbulence development. We will discuss different classes of turbulence, its evolution, and observational signatures including gravitational waves, effects on cosmic microwave background, large scale structure formation, and others.
The nature of dark matter is one of the most longstanding and puzzling questions in physics. With cosmological measurements we have been able to measure its abundance with great precision. Yet, what dark matter is composed of remains a mystery.
In 2016 the first ever observation of gravitational waves from the coalescence event of two black holes was achieved by the LIGO interferometers.
Together with my collaborators we advocated that the interactions of 30 solar masses primordial black holes composing the dark matter could explain this event.
This opens up a new window in indirect searches for dark matter.
In my talk, I will discuss the various probes to distinguish between these mergers of primordial black holes, from the more traditional astrophysical black hole binaries.
One is through their mass spectrum, an other is through cross-correlation of gravitational events with future overlapping galaxy catalogs. A third, is through their contribution to the stochastic gravitational wave background. Finally a fourth probe uses the fact that primordial black black holes form binaries with highly eccentric orbits. Those will then merge on timescales that in some cases are years, days or even minutes, retaining some eccentricity in the last seconds before the merger, which can be detected by LIGO and future ground based interferometers.
Recent detections by LIGO have shown evidence of black hole mergers in the galaxy. While current black hole formation is well understood, numerous works have investigated methods through which they could be created in the early universe. We investigate constraints on the abundance of these black holes known as primordial black holes (PBHs) in the mass range $10^{15}-10^{17}$ g using data from the Cosmic Microwave Background (CMB) and extragalactic gamma-ray background (EGB). PBHs in this mass range emit energy through Hawking radiation which leaves an imprint on the CMB through modification of the ionization history and the damping of CMB anisotropies. Using a model for redshift dependent energy injection efficiencies, we show that a combination of temperature and polarization data from Planck provides the strongest constraint on the abundance of PBHs for masses $\sim 10^{15}-10^{16}$ g, while the EGB dominates for masses $\gt 10^{16}$ g. Both the CMB and EGB now rule out PBHs as the dominant component of dark matter for masses $\sim 10^{15}-10^{17}$ g. Planned MeV gamma-ray observatories are ideal for further improving constraints on PBHs in this mass range.
The gravitational waves measured at LIGO are presumed here to come from merging primordial black holes. We ask how these primordial black holes could arise through inflationary models while not conflicting with current experiments. Among the approaches that work, we investigate the opportunity for corroboration through experimental probes of gravitational waves at pulsar timing arrays. We provide examples of theories that are already ruled out, theories that will soon be probed, and theories that will not be tested in the foreseeable future. The models that are most strongly constrained are those with a relatively broad primordial power spectrum.
Primordial black holes evaporate by Hawking radiation, leaving a stochastic gravitational-wave background today. Its spectrum is affected by the formation mass, angular momentum and initial abundance. In particular, the particle emission is greatly enhanced at high frequencies for fast-rotating black holes. In this work, we calculated this spectrum for a wide range of these parameters. Besides, we used the latest constraints on the abundance and found the upper bound on today's spectral density of gravitational waves.
Since the detection of the gravitational wave(GW) signals by LIGO, an increasing attention has been given to the GWs generated during the first order Electroweak phase transition(EWPT), a process essential for a successful generation of the baryon asymmetry in the universe. I will present in this talk a scenario where such GWs are generated during a two step EWPT triggered by the dark matter and discuss its discovery prospects in spaced-based interferometers as well as implications on the model from requirement of a strongly first order EWPT and dark matter phenomenology. I will future explore the complementarity in determining the Higgs couplings between measurements at colliders and GW detections. This talk is based mainly on the recent work arxiv:1702.02698.
The recent measurements of the Cosmic Microwave Background (CMB) from the Planck telescope, and of the Large Scale Structure (LSS) from diﬀerent experiments, have conﬁrmed the standard model of cosmology, or $\Lambda CDM$. Nevertheless, many alternative cosmological models are also consistent with this data. Some mild tensions between Planck, the measurement of the Hubble parameter ($H_0$), and these LSS experiments (concretely speaking, of the Matter Power Spectrum for sizes of $8h^{-1}$Mpc ($\sigma_8$)) hint to models beyond ΛCDM.
In this talk I present a recent proposal for a Dark Sector which consists of two components: a cold Dark Matter one, and another of Dark Radiation, along with their mutual interactions. The presence of the Dark Radiation alleviates the tension in the measurement of $H_0$, while the interactions address the discrepancy in $\sigma_8$.
I describe the mechanism with which this model deals with the mentioned tensions, using the equations for the evolution of the cosmological anisotropies, as well as examples of their particle physics realizations. In addition, I present simple analytical solutions for two interesting limits of this model. Finally, I show the ﬁt of this model to the cosmological data and compare it to that of $\Lambda CDM$.
The composition of the primary particle in cosmic ray air showers is of general interest. Measuring the penetration depth of showers allows for template fits of this composition. We use simple generic new physics models to compare the penetration depth distribution of new physics versus primary composition. We argue that complementary information is needed to disentangle these effects and show our findings for the number of muons reaching the ground.
In this talk, I will discuss the effect of (strongly coupled) new physics in the di-boson final states at the HL-LHC in an EFT frame work. We will focus on the operators (dimension-six and dimension-eight) which will generate the energy-growing behaviour in the di-boson processes, thus can be possible to beat LEP Z-pole precision. We also interpret the projection bounds on the mass scales in different scenarios, mainly focus on the strongly coupled theory.
We investigate composite Higgs models based on $SO(5) \times U(1)$ in the framework of gauge-Higgs unification in $AdS_5$. To create a Little Hierarchy, we introduce a top partner that competes with the top quark in the generation of the Higgs potential. We also make use of the freedom to adjust the gauge couplings with UV boundary kinetic term. Our model space is still only two-dimensional after the masses of known particles are fixed. Precision electroweak observables give the most significant constraint on the scale of new physics. Top partners and gauge boson resonances in our model are accessible at colliders and we study the relation of the resonance masses to precision observables such as the Higgs boson and top quark couplings. This will aid in understanding the constraints on composite Higgs models from the LHC and future accelerators such as ILC.
We investigate the possibility to find an ultraviolet completion of extensions of the Standard Model where baryon number is a local symmetry. A simple theory based on SU(4)C ⊗ SU(3)L ⊗ SU(3)R where baryon number is embedded in a non-Abelian gauge symmetry is introduced. We discuss the main features of the theory and the possible implications for experiments.
It is shown that in SO(10) models, a Yukawa sector consisting of a real $10_H$, a real
$120_H$ and a complex $126_H$ of Higgs fields can provide a realistic fit to all fermion
masses and mixings, including the neutrino sector. Although the group theory of
SO(10) demands that the $10_H$ and $120_H$ be real, most constructions complexify these
fields and impose symmetries exterior to SO(10) to achieve predictivity. The proposed
new framework with real $10_H$ and real $120_H$ relies only on SO(10) gauge symmetry,
and yet has a limited number of Yukawa parameters. This analysis shows that while
there are restrictions on the observables, a good fit to the entire fermion spectrum
can be realized. Unification of gauge couplings is achieved with an intermediate scale
Pati-Salam gauge symmetry. Proton decay branching ratios are calculable, with the
leading decay modes being $p → ν π^+$ and $p → e π^0$.
Giving up the solutions to the fine-tuning problems, we propose the non-supersymmetric flipped $SU(5)\times U(1)_X$ model based on the minimal particle content principle. To achieve gauge coupling unification, we introduce one pair of vector-like fermions, which form complete $SU(5)\times U(1)_X$ representation.
Proton lifetime is around $5\times 10^{35}$ years, neutrino masses and mixing can be explained via seesaw mechanism,baryon asymmetry can be generated via leptogenesis, and vacuum stability problem can be solved as well. In particular, we propose that inflaton and dark matter particle can be unified to a real scalar field with $Z_2$ symmetry, which is not an axion and does not have the non-minimal coupling to gravity. Such kind of scenarios can be applied to the
generic scalar dark matter models. Also, as one of realistic examples in our model, we find that the vector-like particle corrections to the SM prediction of the mixing $M_{12}$ for $B_s^0$ can be about 6.6%, while their corrections to the $K^0$ and $B_d^0$ are negligible.
In original twin Higgs model, vacuum misalignment between electroweak and new physics scales is realized by adding explicit Z2 breaking term. Introducing additional twin Higgs could accommodate spontaneous Z2 breaking, which explains the origin of this misalignment. I will talk about scenarios on realising the vacuum misalignment in a natural two Higgs double model framework: explicit Z2 breaking, radiative Z2 breaking, tadpole-induced Z2 breaking, and quartic-induced Z2 breaking. I will address on the radiative Z2 breaking, in which the Z2 symmetry is spontaneously broken and the Higgs potential is fully radiatively generated.
Twin Higgs models solve the little hierarchy problem without introducing new colored particles, however they are often in tension with measurements of the radiation density at late times. I will explore viable cosmological histories for Twin Higgs models where the mixing between the SM and twin neutrinos can thermalize the two sectors below the twin QCD phase transition, significantly reducing the twin sector’s contribution to the radiation density. The requisite twin neutrino masses of O(1 − 20) GeV and mixing angle with SM neutrinos can be probed in a variety of current and planned experiments. These parameters are naturally accessed in a warped UV completion, where the composite twin neutrino sector can also generate the Z2-breaking Higgs mass term needed to produce the hierarchy between the symmetry breaking scales f and v.
Theories of neutral naturalness, where the Standard Model top partner carries no Standard Model charge, may explain the lack of new physics seen at the LHC. The Twin Higgs was the first of these theories to be introduced, but recent work has demonstrated it is only an isolated example in a large class of "orbifold Higgs" models. In this work we study an orbifold Higgs model resulting from the orbifold projection by the non-abelian group $S_3$. A model with multiple sectors uncharged under the Standard Model emerges. Constraints are placed on the model from Higgs phenomenology and the prospects of finding evidence in colliders are discussed.
The observation of a new particle in the search for the Standard Model Higgs boson by the ATLAS and CMS
experiments represents a major breakthrough in our understanding of the mechanism of the electroweak symmetry breaking.
Current measurements of the spin and parity of this new particle, as well as the investigation of its couplings to other SM particles, revealed no significant deviation
from the corresponding predictions for the Standard Model Higgs boson.
With the increase of centre-of-mass energy and high integrated luminosity achieved at Large Hadron
Collider in 2015-2017, the properties of recently discovered Higgs boson can be studied in further details.
In this presentation latest updates on cross sections and couplings analyses of the Higgs Boson are presented.
The discussion will focus on the recent results obtained by the ATLAS collaboration in Higgs di-boson decay channels.
Study of the CP parity of a Higgs boson and its anomalous couplings to gauge bosons or fermions is one of the priorities of the LHC and future Higgs factories. We present a coherent framework for the measurement of anomalous couplings of the Higgs boson to two weak vector bosons using the decay, vector boson fusion production, and associated production with a vector boson, where both on-shell and off-shell Higgs boson production is considered. We include interference with background processes where relevant. The framework also allows the study of anomalous couplings of the Higgs boson to fermions in ttH, bbH, tqH production and in H->tau tau decay. Particular emphasis is placed on the tools, which include the Monte Carlo generator, re-weighting techniques for fast simulation of anomalous interactions, and matrix element techniques for the optimal analysis of the processes. The formalism is presented using both the effective field theory and effective scattering amplitudes, where the dependence on the virtuality of the weak and Higgs bosons is also tested with form factors. The capabilities of the framework are illustrated with the projections for measuring CP-violating properties of the Higgs boson at the LHC and future Higgs factories.
At the LHC, the most promising channel for probing the coupling of the Higgs field to the quarks and leptons are H->bb and H->tautau, respectively. In this talk I will be presenting the latest ATLAS results on these two channels. The rare H->mumu decay is also investigated. In many scenarios beyond the standard model (BSM) the couplings of the Higgs to fermions is altered. In ATLAS many BSM searches involving Higgs fermionic decays take place.
We study the Higgs boson $(h)$ decay to two light jets at the 14 TeV High-Luminosity-LHC (HL-LHC), where a light jet ($j$) represents any non-flavor tagged jet from the observational point of view.
% On the theory side, $j$ is a gluon as expected in the Standard Model}.
The decay mode $h\to gg$ is chosen as the benchmark since it is the dominant channel in the Standard Model (SM), but the bound obtained is also applicable to the light quarks $(j=u,d,s)$. We estimate the achievable bounds on the decay branching fractions through the associated production $Vh\ (V=W^\pm,Z)$. Events of the Higgs boson decaying into heavy (tagged) or light (un-tagged) jets are correlatively analyzed.
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We find that with 3000 fb$^{-1}$ data at the HL-LHC, we should expect approximately $1\sigma$ statistical significance on the SM $Vh(gg)$ signal in this channel. This corresponds to a reachable upper bound ${\rm BR}(h\to jj) \leq 4~ {\rm BR}^{SM}(h\to gg)$ at $95\%$ confidence level.
A consistency fit also leads to an upper bound
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${\rm BR}(h\to cc) < 15~ {\rm BR}^{SM}(h\to cc)$ at $95\%$ confidence level.
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The estimated bound may be further strengthened by
adopting multiple variable analyses, or adding other production channels.
The radiative decays of the Higgs boson to a fermion pair $h\rightarrow f\bar{f}\gamma$ is revisited, where $f$ denotes a fermion in the Standard Model (SM). Both the chirality-flipping diagrams via the Yukawa couplings at the order $\mathcal{O}(y_f^2 \alpha)$, and the chirality-conserving contributions via the top-quark loops of the order $\mathcal{O}(y_t^2 \alpha^3)$ and the electroweak loops at the order $\mathcal{O}(\alpha^4)$, are included. The QED correction is about $Q_f^2\times {\cal O}(1\%)$ and contributes to the running of fermion masses at a similar level, which should be taken into account for future precision Higgs physics.
The chirality-conserving electroweak-loop processes are interesting from the observational point of view. First, the branching fraction of the radiative decay $h \to \mu^+\mu^- \gamma$ is about a half of that of $h \to \mu^+\mu^-$, and that of $h \to e^+ e^- \gamma$ is more than four orders of magnitude larger than that of $h \to e^+ e^-$, both of which reach about $10^{-4}$. The branching fraction of $h \to \tau^+\tau^- \gamma$ is of the order $10^{-3}$.
All the leptonic radiative decays are potentially observable at the LHC Run 2 or the HL-LHC.
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The kinematic distributions for the photon energy or the fermion pair invariant mass provide non-ambiguous discrimination for the underlying mechanisms of the Higgs radiative decay. The process $h \to c\bar c \gamma$ and evaluate the observability at the LHC will be discussed. It turns out to be comparable to the other related studies and better than the $h \to J/\psi\ \gamma$ channel in constraining the charm-Yukawa coupling.
We present the latest results on hh searches at the CMS experiment.
The measurement of the Higgs trilinear coupling through Higgs pair production is particularly challenging. We explore the possibility of probing the trilinear coupling indirectly, through the production and decay of a single Higgs. The method relies on the effects that electroweak
loops featuring an anomalous trilinear coupling would imprint on single Higgs
production at the LHC. We find that the bounds on the self coupling are already competitive with those from Higgs pair production and will be further improved in the current and next LHC runs.
Recently it has been suggested that precision single-Higgs measurements offer an alternative approach to the extraction of the Higgs self coupling with respect the traditional double-Higgs searches. We study how to obtain a parametrically enhanced deviation of the Higgs self-coupling and we estimate how large this deviation can be in a self-consistent EFT framework. We perform a global study on the impact that large deviations on the trilinear might have on the determination of single-Higgs couplings. We advocate that new observables are needed to resolve a degeneracy that appears at large Higgs self-coupling, leading to an interesting interplay between diboson production, single-Higgs data and double Higgs analysis.
Dark matter (DM) is currently one of the most striking hints of new physics.
Its existence is suggested by many astrophysical observations, yet the Standard
Model of particle physics does not provide any candidate particle to explain its
abundance in the universe. According to some theoretical models, DM is made
of weakly interacting massive particles with masses at the TeV scale.
This assumption is consistent with the observed DM density and implies the possible direct production of DM at hadron colliders.
The CMS experiment at the CERN Large Hadron Collider has an extensive
search program focused on DM. This talk describes the analysis strategy and
the current status of the search for DM at CMS based on almost 40 fb^{-1} of data
collected at 13 TeV in 2016. The discovery potential, in view of the forthcoming LHC restart, is also discussed.
If invisible particles are produced at colliders, their information is encoded into the kinematic distributions of visible particles. Although it sounds trivial, the problem is how systematically and efficiently they can be extracted. At least for models with s-channel mediator, we provide simple method and we test it within simplified model as an example.
In this talk, I will discuss the phenomenology of some gauge invariant Higgs portal Dark Matter (DM) models. When DM is fermion, applying the Standard Model (SM) gauge symmetry to simplified DM model will introduce an extra scalar mediator in addition to the SM Higgs. This has two consequences: processes of two scalar mediators will interfere with each other; there will be new signals at collider such as scalar to scalar decay. Moreover, I will discuss how to discriminate the spin of DMs in the gauge invariant Higgs portal scenarios at the ILC.
We consider minimal dark matter scenarios featuring momentum-dependent couplings of the dark sector to the Standard Model. We derive constraints from existing LHC searches in the monojet channel, estimate the future LHC sensitivity for an integrated luminosity of 300 fb−1, and compare with models exhibiting conventional momentum-independent interactions with the dark sector. In addition to being well motivated by (composite) pseudo-Goldstone dark matter scenarios, momentum-dependent couplings are interesting as they weaken direct detection constraints. For a specific dark matter mass, the LHC turns out to be sensitive to smaller signal cross-sections in the momentum-dependent case, by virtue of the harder jet transverse-momentum distribution.
We consider a concise dark matter (DM) scenario in the context of a non-exotic U(1) extension of the Standard Model (SM), where a new U(1)_X gauge symmetry is introduced along with three generation of right-handed neutrinos (RHNs) and an SM gauge singlet Higgs field. The model is a generalization of the minimal gauged U(1)_B-L (baryon number minus lepton number) extension of the SM, in which the extra U(1)_X gauge symmetry is expressed as a linear combination of the SM U(1)_Y and U(1)_B-L gauge symmetries. We introduce a Z_2-parity and assign an odd-parity only for one RHN among all particles, so that this Z_2-odd RHN plays a role of DM. The so-called minimal seesaw mechanism is implemented in this model with only two Z_2-even RHNs. In this context, we investigate physics of the RHN DM, focusing on the case that this DM particle communicates with the SM particles through the U(1)_X gauge boson (Z' boson). This "Z'-portal RHN DM" scenario is controlled by only three free parameters: the U(1)_X gauge coupling, the Z' boson mass, and the U(1)_X charge of the SM Higgs doublet. We consider various phenomenological constraints to identify a phenomenologically viable parameter space. The most important constraints are the observed DM relic abundance and the latest LHC Run-2 results on the search for a narrow resonance with the di-lepton final state. We find that these are complementary with each other and narrow the allowed parameter region, leading to the lower mass bound of > 2.7 TeV.
We study a family of simplified models in which dark matter (DM) interacts with both quarks and leptons through a renormalizable Yukawa interaction with partner fields. The partners are complex scalar fields if DM is fermionic and Dirac fields if DM is scalar. We study how these type of interactions can reshape the spectra of the lepton pair production at the LHC as a function of the properties of the dark sector (e.g. DM spin, mass, couplings). We found that the dilepton invariant mass allows one to distinguish the spin of DM in the limit in which the mediator and the DM mass are almost degenerate. Furthermore, using the angular distribution in the Collin-Soper frame, it is possible to identify the relative chirality between the Standard Model (SM) fermions that interact with the dark sector. We set bounds on the mass and the coupling of DM with the visible sector, in the cases in which the mediator masses are between 10 and 100 percent above the DM mass. In most of the region of parameter space here explored, dilepton distributions place stronger bounds than the ones from jets+MET searches.
Models of dark matter which couple to the Standard Model primarily through the top quark are well motivated from theoretical and experimental perspectives. Possible top-philic dark matter models and their motivations will be explored. Ultimately, simplified models which encapsulate the characteristics of interest will be used to examine recent LHC results as well as direct and indirect detection searches.
We look at a simplified model for dark matter interacting with quarks mediated by heavy colored scalars. In particular, we study the contribution from dark matter scattering against gluons from the nuclei, which arises at 1-loop. We
determine relevant Wilson coefficients and also analyze the effects of RG Evolution on the same.
We present our preliminary results and identify dominant contributions to dark matter - nucleon scattering.
Mini-review: Supersymmetry phenomenology at the LHC
In this talk an overview of the recent CMS searches for supersymmetry in fully hadronic final states will be presented. These searches were performed using 36\fb of pp collision data at 13 TeV, collected during 2016. The results provide the strongest limits to date on the masses of pair-produced squarks and gluinos.
Despite the absence of experimental evidence, weak scale supersymmetry remains one of the best motivated and studied Standard Model extensions. This talk summarises recent ATLAS results on inclusive searches for supersymmetric squarks and gluinos, including third generation squarks produced in the decay of gluinos. The searches involve final states containing jets, missing transverse momentum with and without light leptons, taus or photons, and were performed with pp collisions at a centre-of-mass energy of 13 TeV.
Radiatively-driven natural SUSY (RNS) models enjoy electroweak
naturalness at the 10\% level while respecting LHC sparticle and Higgs
mass constraints. Gluino and top squark masses can range up to several
TeV (with other squarks even heavier) but a set of light Higgsinos are
required with mass not too far above $m_h\sim 125$ GeV. Within the RNS
framework, gluinos dominantly decay via
$\tilde{g} \to t\tilde t_1^{*},\ \bar{t}\tilde t_1 \to t\bar{t}\widetilde Z_{1,2}$ or
$t\bar{b}\widetilde W_1^-+c.c.$,
where the decay products of the higgsino-like
$\widetilde W_1$ and $\widetilde Z_2$ are very soft. Gluino pair production is, therefore,
signalled by events with up to four hard $b$-jets and large $\not\!\!{E_T}$. We
devise a set of cuts to isolate a relatively pure gluino sample at the
(high luminosity) LHC and show that in the RNS model with very heavy
squarks, the gluino signal will be accessible for $m_{\tilde g} < 2400 \
(2800)$~GeV for an integrated luminosity of 300 (3000)~fb$^{-1}$. We
also show that the measurement of the rate of gluino events in the clean
sample mentioned above allows for a determination of $m_{\tilde g}$ with a
statistical precision of 2-5% (depending on the integrated luminosity
and the gluino mass) over the range of gluino masses where a 5$\sigma$
discovery is possible at the LHC.
Supersymmetric theories offer an elegant solution to the naturalness problem of the Standard Model Higgs, constraining the mass of the superpartners of the third generation quarks, the stop and the sbottom, to be below the TeV scale. This talk presents the status of the ATLAS searches for direct pair production of third generation squarks. It presents an overview of the latest public analyses carried out during the Run 2 of the Large Hadron Collider (LHC) using statistics of 2015 and 2015+2016 proton-proton collisions at $\sqrt{s} = 13$ TeV collected by the ATLAS detector.
Naturalness arguments for weak-scale supersymmetry prefer the superpartners of
the third generation quarks (stop and sbottom) with masses close to the
electroweak scale, which can be produced at the LHC. This talk presents recent
CMS results from searches for direct stop and sbottom pair production, using
data collected in proton-proton collisions, at a center-of-mass energy of 13
TeV, corresponding to an integrated luminosity of 36/fb.
The Higgs pair production in gluon fusion is a sensitive probe of beyond-Standard Model (BSM) phenomena. Motivated by the combined analysis of ATLAS and CMS Higgs production data, which allows moderate deviations of the Higgs couplings with respect to their Standard Model (SM) values, we show that the Higgs pair production may be significantly increased with respect to the SM predictions in a simplified model with light stops and staus allowed by the latest LHC search bounds. We also explore the implications of such modification of the cross-section in the context of discovering the deviation in the triple Higgs coupling from the SM value, which is strongly correlated with First order phase transitions of the scalar potential in many models e.g. NMSSM.
The two Higgs doublet model allows for correlated enhancements of $t \bar{t} h$ and di-Higgs production rates, consistent with known properties of the Higgs boson. Results of our analysis will be presented.
With the discovery of Standard Model(SM) Higgs boson at the LHC, exploring the thermal history associated with electroweak symmetry-breaking (EWSB) has taken on heightened interest. The process of the electroweak phase transition (EWPT) in early universe provides conditions able to explain the observed cosmic matter-antimatter asymmetry, if the transition were of first order and sufficiently strong. The prospects for resonant di-Higgs production searches at LHC, in the context of probing the EWPT in Higgs portal extension of the SM, will be presented. We explore the sensitivity of the $b \bar{b} W^{+} W^{-}$ channel, with $W$ leptonic decays. The presence of neutrinos in the final state does not allow the reconstruction of the invariant mass of the heavy scalar, diminishing the sensitivity of this channel. We present a novel technique, called Heavy Mass Estimator (HME), that allows to fully reconstruct the kinematic of the process, and therefore to reconstruct the heavy Higgs invariant mass. We prove that, with HME technique, this channel can be sensitive as much as $b\bar{b}b\bar{b}$, $b\bar{b}\gamma\gamma$, and $b\bar{b}\tau\tau$ channels, leading to a potential discovery of resonant di-Higgs production with the datasets accumulated in High Luminosity phase of LHC, foreseen in 2035
The simplest extension of the Standard Model is the singlet extended Standard Model. This model adds a gauge singlet scalar, $S$, which has interactions with the Standard Model Higgs doublet. For a sufficiently heavy new scalar and in the absence of a $Z_2$ symmetry $S\rightarrow -S$, this model can lead to resonant double Higgs production, which leads to a significant increase in production rates over the predictions of the Standard Model. Many Standard Model extensions include singlets, so this extension is fairly generic. We determine benchmarks by maximizing the double Higgs production rate at the LHC in the singlet extended Standard Model. Within current experimental constraints, the branching ratio of the new scalar into two Standard Model-like Higgs bosons can be upwards of $0.76$ and the double Higgs rate can be increased upwards of 30 times the Standard Model prediction for certain values of the new scalar mass.
One of the simplest extensions of the Standard Model is the inclusion of an additional scalar multiplet, and we consider
scalars
in the $SU(2)_L$ singlet, triplet, and quartet representations. We
consider models with heavy neutral scalars, $m_H\sim 1-2$ TeV, and the matching of the UV complete theories to
the low energy effective field theory. We demonstrate the
agreement of the kinematic distributions obtained in the singlet models for the gluon fusion of a Higgs pair
with the predictions of the effective field theory at $\sqrt{S} = 13$ and $100$ TeV.
The restrictions on the extended scalar sectors due to perturbative unitarity and precision electroweak measurements are
summarized and lead to highly restricted regions of viable parameter space for the triplet and quartet models.
Several theories beyond the Standard Model predict enhanced production rates for Higgs Boson pair production. Other theories predict Lepton Flavour Violating decays of the Higgs boson or enhanced decay rates into rare modes like Z-photon, J/Psi-photon, Phi-photon or into pairs of light pseudoscalar bosons "a". In this presentation the latest ATLAS results on searches for these particles will be discussed.
The transverse momentum distribution of the Higgs at large $P_T$ is complicated by its dependence on three important energy scales: $P_T$, the top quark mass $m_t$, and the Higgs mass $m_H$. A strategy for simplifying the calculation of the cross section at large $P_T$ is to calculate only the leading terms in its expansion in $m_t^2/P_T^2$ and/or $m_H^2/P_T^2$. The expansion of the cross section in inverse powers of $P_T$ is complicated by logarithms of $P_T$ and by mass singularities. In this paper, we consider the top-quark loop contribution to the subprocess $q\bar{q}\to H+g$ at leading order in $\alpha_s$. We show that the leading power of $1/P_T^2$ can be expressed in the form of a factorization formula that separates the large scale $P_T$ from the scale of the masses. All the dependence on $m_t$ and $m_H$ can be factorized into a distribution amplitude for $t \bar t$ in the Higgs, a distribution amplitude for $t \bar t$ in a real gluon, and an endpoint contribution. The factorization formula can be used to simplify calculations of the $P_T$ distribution at large $P_T$ to next-to-leading order in $\alpha_s$.
We suggest that the exclusive Higgs + light (or b) jet production at the LHC,
$pp \to h+j(j_b)$, is a rather sensitive probe
of the light-quarks Yukawa couplings and of new physics (NP) in the
Higgs-gluon $hgg$ and quark-gluon $qqg$ interactions.
We study the Higgs $p_T$ distribution in $pp \to h+j(j_b)$, employing non-differential observables
to probe the different types of NP relevant for this process, which we parameterize
either as scaled SM couplings (the kappa-framework) and/or
as new higher dimensional effective operators (the SMEFT framework).
We find that the exclusive $h+j(j_b)$ production
at the 13 TeV LHC is sensitive to various NP scenarios,
with typical scales ranging from a few to O(10) TeV, depending
on the flavor, chirality and Lorentz structure of the underlying physics.
There has been a great deal of interest in the Left Right symmetric electro-weak gauge theory in recent years due to its potential accessibility at the LHC. The scalar sector of the minimal left right symmetric model (MLRSM) at TeV scale is revisited in light of the photon initiated processes at the large hadron collider (LHC). Without introducing any guest particles and just by adding an extra soft breaking term in MLRSM Higgs potential, we have shown that it is possible to search for the neutral heavier Higgs bosons at the LHC without conflicting with flavor changing neutral Higgs (FCNH) constraints. We have pointed out some tests as well as its potential for discovery of the second Higgs at the LHC. The photon-photon fusion process contributes significantly to the pair production of doubly charged Higgs bosons also at a level comparable to the Drell-Yan production. As a result, the reported experimental lower limit on the mass of $\Delta_{L}^{\pm\pm}$ ($\Delta_{R}^{\pm\pm}$) arising from $SU(2)_L$ triplet (singlet) scalar will be improved by including the photon initiated process. The results can be taken as an initial guide in the exploration of the heavy fermiphobic as well as hadrophobic Higgs at colliders via photon initiated process.
We study the constraints on neutralino dark matter in minimal low energy supersymmetry models and the case of heavy lepton and quark scalar superpartners.
For values of the Higgsino and gaugino mass parameters of the order of the weak
scale, direct detection experiments are already putting strong bounds on models
in which the dominant interactions between the dark matter candidates and nuclei
are governed by Higgs boson exchange processes, particularly for positive values of
the Higgsino mass parameter ?. For negative values of higgsino mass?, there can be destructive
interference between the amplitudes associated with the exchange of the standard
CP-even Higgs boson and the exchange of the non-standard one. This leads to speci?c regions of parameter space which are consistent with the current experimental
constraints and a thermal origin of the observed relic density. In this talk, I am going to discuss
the current experimental constraints on these scenarios, as well as the future experimental probes, using a combination of direct and indirect dark matter detection and
heavy Higgs and electroweakino searches at hadron colliders.
We study an MSSM scenario in which the only light sparticles are a bino-like
dark matter candidate, and one or more light-flavored squarks. We find that this
scenario has several interesting phenomenological features. In particular, LHC
searches for the light squarks have reduced sensitivity, since the visible and
invisible products tend to be softer. Moreover, bino-squark co-annihilation can
allow even relatively heavy dark matter candidates to be consistent thermal relics.
Finally, the dark matter nucleon scattering cross section is enhanced in the
squeezed limit, allowing direct detection experiments to use both spin-independent
and spin-dependent scattering to probe regions of parameter space beyond the those
probed by the LHC. Although we have phrased this study in terms of the MSSM, the
results generalize to models in which a gauge-singlet Majorana fermion dark matter candidate
interacts with quarks via new charged scalars.
The most dramatic "Sommerfeld enhancements" of neutral-wino-pair annihilation occur when the wino mass is tuned to near critical values where there is a zero-energy S-wave resonance at the neutral-wino-pair threshold. If the wino mass is larger than the critical value, the resonance is a wino-pair bound state. If the wino mass is near a critical value, low-energy winos can be described by a zero-range effective field theory in which the winos interact nonperturbatively through a contact interaction. The effective field theory is controlled by a renormalization group fixed point at which the neutral and charged winos are degenerate in mass and their scattering length is infinite. The parameters of the zero-range effective field theory can be determined by matching wino scattering amplitudes calculated by solving the Schrödinger equation for winos interacting through a potential due to the exchange of weak gauge bosons. The power of the zero-range effective field theory is illustrated by calculating the rate for formation of the bound state in the collision of two neutral winos through the emission of two soft photons.
The spectrum of Weakly-Interacting-Massive-Particle (WIMP) dark matter generically possesses bound states when the WIMP mass becomes sufficiently large relative to the mass of the electroweak gauge bosons. The presence of these bound states enhances the annihilation rate via resonances in the Sommerfeld enhancement, but they can also be produced directly with the emission of a low-energy photon. In this work we compute the rate for SU(2) triplet dark matter (the wino) to bind into WIMPonium — which is possible via single-photon emission for wino masses above 5TeV for relative velocity v < O(10^-2) — and study the subsequent decays of these bound states. We present results with applications beyond the wino case, e.g. for dark matter inhabiting a nonabelian dark sector.
The minimal supersymmetric setup offers a comprehensive framework to interpret the Fermi–LAT Galactic center excess. Taking into account experimental, theoretical, and astrophysical uncertainties we can identify valid parameter regions linked to different annihilation channels. They extend to dark matter masses above 250 GeV. There exists a very mild tension between the observed relic density and the annihilation rate in the center of our galaxy for specific channels. The strongest additional constraints come from the new generation of direct detection experiments, ruling out much of the light and intermediate dark matter mass regime and giving preference to heavier dark matter annihilating into a pair of top quarks.
We study a multi-component dark matter model where interactions with the Standard Model are primarily via the Higgs boson. The model contains vector-like fermions charged under SU(2)W × U(1)Y and under the dark gauge group, U(1)′. This results in two dark matter candidates. A spin-1 and a spin-1/2 candidate, which have loop and tree-level couplings to the Higgs, respectively. We explore the resulting effect on the dark matter relic abundance, while also evaluating constraints on the Higgs invisible width and from direct detection experiments. Generally, we find that this model is highly constrained when the fermionic candidate is the predominant fraction of the dark matter relic abundance.
Fermionic dark matter is added to the Froggatt-Nielsen mechanism, and conditions for freezeout identified. DM is charged under $U(1)_{FN}$, with the dominant annihilation channel a CP-even flavon $+$ CP-odd flavon. When the DM-flavon coupling strength $\sim$ the Cabibbo angle (0.23): (1) the DM mass is $\mathcal{O}$(100 GeV - 1 TeV), (2) perturbativity puts a lower and upper limits on the flavor scale,
(3) DM is a secluded WIMP effectively hidden from collider and direct detection searches.
Low-energy flavor experiments limiting the masses of dark matter and mediators constitute the best constraints on this scenario, while Fermi-LAT observations of dwarf galaxies, and collider searches for missing energy plus a single jet/bottom/top, are promising avenues for future discovery.
Identifying signatures of dark matter at indirect-detection experiments is generally more challenging in non-minimal dark-matter scenarios than it is in scenarios involving a single dark particle. The reason is that the partitioning of the total dark-matter abundance across an ensemble of particles with different masses tends to "smear" the injection spectra of photons and other cosmic-ray particles produced via dark-matter annihilation or decay, leading to continuum features rather than sharp lines. In this talk, I shall discuss two strategies for identifying characteristic signatures of non-minimal dark-matter scenarios at indirect-detection experiments. One of these strategies exploits correlations that arise between different continuum spectral features associated with the same annihilation or decay process. The other involves the identification of an "energy duality" under which a single spectral feature is invariant. I shall also discuss potential implications of this latter strategy for assessing the origin of the observed excess of gamma-rays emanating from the Galactic Center within the context of the Dynamical Dark Matter framework.
In the Dynamical Dark Matter (DDM) framework, the dark sector comprises a vast ensemble of particle species whose Standard-Model decay widths are balanced against their cosmological abundances. In this talk, we present a new class of DDM ensembles in which the masses of the dark states lie along linear Regge trajectories and the density of dark states grows exponentially with mass. Ensembles with these properties arise naturally as the “hadronic” resonances associated with the confining phase of a strongly-coupled dark sector; they also arise naturally as the gauge-neutral bulk states of Type I string theories. We study the dynamical properties of such ensembles and map out their corresponding viable parameter spaces. We find that viable DDM ensembles of this sort exist with fundamental energy scales ranging from the GeV scale all the way to the Planck scale, but that many internal aspects of these theories exhibit surprising, non-trivial correlations.
Mini-review: Theory of neutrino mass and lepton flavors
In this talk I will construct a flavor model with a gauge boson below the weak scale. The model is viable and shows the synergy between low energy observables, meson decays, neutrino oscillations, and LHC physics. The role of neutrinos will be highlighted.
The existence for three otherwise identical copies of the standard model fermions with widely disparate masses remains one of the great mysteries of modern particle physics. In this talk, I will introduce a framework, based on a continuous symmetry, for explaining the masses and mixings of the standard model fermions, with particular emphasis on neutrinos, and will discuss means by which this framework can be probed.
We revisit heavy neutrino production via gluon fusion $gg \rightarrow h^* /Z^* \rightarrow Nv$, and its relative importance at hadron colliders with respect to the charged current Drell-Yan $q\overline{q'} \to W^* \to N\ell$ and the vector boson fusion $q\gamma \overset{W\gamma \to N\ell}{\to} q' N\ell$ processes.
In this context, we present, for the first time, resummed threshold contributions to the gluon fusion channel. We discuss also the phenomenological impact of such corrections for the large hadron collider and hypothetical 100 TeV very large hadron collider.
The discovery of neutrino oscillations calls for an extension of the Standard Model that would generate neutrino masses and mixing. One of the simplest possibilities is the addition of fermionic gauge singlets or sterile neutrinos. TeV-scale realisations of this idea lead to a very rich phenomenology due to the mixing of the new fermions with the left-handed neutrinos of the SM and the large Higgs-neutrino coupling. In a first study, we showed in a simplified 3+1 model with Dirac neutrinos that loops with a heavy neutrino can induce large corrections, up to 30% of the SM one-loop value. These effects are potentially larger in low-scale seesaw models, as we showed by considering the inverse seesaw. I will discuss how fermionic singlets induce large corrections to the triple Higgs coupling and how they can be used to probe neutrino mass models in a regime otherwise difficult to access.
The existence of tiny neutrino masses at a scale more than a million times smaller than the lightest charged fermion mass, namely the electron, and their mixings can not be explained within the framework of the exceptionally successful Standard Model. There are four ideas that has been proposed to explain the tiny neutrino masses. These include the see-saw mechanism with a right-handed neutrino at the GUT scale, and this is the most elegant mechanism. The other mechanisms are radiatively generated neutrino masses, the neutrino mass arising from a 2nd Higgs doublet having a tiny VEV and coupling only to the neutrinos, and finally the mirror model or simply the EW-scale νR model. The mirror model has new quarks and leptons of opposite chirality at the electroweak scale (for the same Standard Model gauge symmetry $SU(2)_W × U(1)_Y$) compared to what we have for the Standard Model. With a suitable modification of the Higgs sector, the EW-scale νR model satisfies the electroweak precision test and also the constraints coming from the observed 125-GeV Higgs scalar. Since in this model, the mirror fermions are required to be in the EW scale, these can be produced at the LHC giving final states with a very low background from the SM. One such final state is the same sign dileptons with large missing pT for the events. In this work, we explore the constraint provided by the 8 TeV data, and the prospect of observing this signal in the 13 TeV runs at the LHC. Additional signals will be the presence of displaced vertices depending on the smallness of the Yukawa couplings of the mirror leptons with the ordinary leptons and the singlet Higgs present in the model. Of particular importance to the EW-scale νR model is the production of νR which will be a direct test of the seesaw mechanism at collider energies.
In this talk, we revisit the dimension seven neutrino mass generation mechanism based on the addition of an isospin $3/2$ scalar quadruplet and two vector-like iso-triplet leptons to the standard model. We discuss the LHC phenomenology of the charged scalars of this model, complemented by the electroweak precision constraints. We pay particular attention to the triply charged and doubly charged components. We focus on the same-sign-tri-lepton signatures originating from the triply-charged scalars and comment on their prospects. On the other hand, doubly charged Higgs has been an object of collider searches for a long time, and we show how the present bounds on its mass depend on the particle spectrum of the theory. Strong constraint on the model parameter space can arise from the measured decay rate of the Standard Model Higgs to a pair of photons.
We develop a systematic procedure of constructing lepton mass matrices that satisfy all the experimental constraints in the light lepton sector of the minimal left-right symmetric model with type-I seesaw dominance. This method is unique since it is applicable to the most general cases of type-I seesaw with complex electroweak vacuum expectation values in the model. Using this method, we investigate the TeV-scale phenomenology without fine-tuning of model parameters when the light neutrino masses have normal hierarchy, with focuses on the charged lepton flavour violation, neutrinoless double beta decay, and electric dipole moments of charged leptons. We examine the predictions for typical ranges of associated observables such as branching ratios of rare lepton decays, and study how those experimental constraints affect the model parameter space. The most notable result is that the model parameter regions that allow very small light neutrino masses are disfavored by the present experimental constraints. Furthermore, we also find that the mass of the lightest heavy neutrino should be relatively small to satisfy those constraints.
Searches for supersymmetry are presented based on the electroweak pair production of neutralinos and charginos in different decay modes of gauginos and sleptons, through intermediate vector bosons or Higgs bosons, or directly to leptons. The data sample corresponds to an integrated luminosity of 35.9 fb$^{-1}$ of pp collisions at a center-of-mass energy of 13 TeV collected in 2016 with the CMS detector at the LHC.
Supersymmetry models with light electroweak sparticles are well motivated by naturalness and have less stringent exclusion limits on the supersymmetric particle masses than strong production. ATLAS searches for electroweak production of supersymmetric particles in a number of channels, which include multiple leptons and therefore benefit from lower numbers of background process events. Results are presented here for searches using $\sqrt{s}=13$TeV ATLAS data collected in 2015 and the most recent findings are summarised.
Supersymmetry has not been observed thus far, which implies that SUSY scale is higher than it was expected before the LHC era. Further, the observation of the Higgs boson mass at $\sim 125$ GeV, implies that the loop correction to the Higgs mass in SUSY is sizable, which in turn also implies a large SUSY scale. An important contributing factor to the non-observation of SUSY is that in most models the large scale of SUSY implies that the neutralino is a Bino and thus one requires co-annihilation to achieve a relic density consistent with WMAP and PLANCK. However, co-annihilation also implies that the mass gap between the LSP and the NLSP is small and thus the final states arising from the decay of the NLSP are soft making the observation of SUSY at the LHC problematic. In this work we investigate the prospects for the discovery of supersymmetry at LHC RUN II in the stau coannihilation region extending the recent work on the stop and gluino coannihilation regions. Our analysis is within the framework of non-universal sugra models with nonuniversality in the gaugino sector. In the analysis we impose the relic density constraints as well as constraints of the Higgs boson mass.
We investigate a large variety of signal regions including those discussed by the ATLAS and the CMS Collaborations but optimized for our parameter space. We analyze the conventional two particle co-annihilation but extend the analysis to include multi-particle co-annihilation. It is found that the signal regions involving $\tau's$ rather than those involving $e,\mu$ are the dominant ones. We have generated benchmarks for the stau co-annihilation regions and give the range of sparticle masses discoverable at LHC RUN II with up to 3000 fb$^{-1}$ of integrated luminosity. The direct detection of neutralino dark matter is analyzed within the class of models investigated. It is found that the spin independent and spin dependent neutralino-proton cross sections lie near the edge of the next generation LUX-ZEPLIN experiments and significantly above the neutrino floor.
In supersymmetry, most solutions to the hierarchy problem feature relatively
light gluinos. For the first time in history we can probe these gluino masses up
to 2 TeV. This talk will motivate searches for gluinos and present search
results and techniques, that focus on supersymmetric models where the gluinos
are believed to be relatively light and that have either one lepton or two
oppositely charged leptons in their final state. The searches are performed on
data corresponding to an integrated luminosity of 36 fb-1 and a center of mass
energy of 13 TeV, recorded with the CMS detector at the CERN LHC in 2016.
Searches for supersymmetry at the Large Hadron Collider in electroweak final states are kinematically limited by softness of the leptonic scattering products in the regime of narrow mass splitting between the slepton and neutralino. After requiring a hard initial-state jet in order to provide the visible system a large transverse boost, we cut on the reconstructed OSSF dilepton mass, as well as the ditau-mass variable and the missing transverse energy. We find that the most difficult residual background is the topologically identical WW+jets final state. We leverage two subtle differences in these processes, namely the mass of the invisible species (zero for background, or around 100 GeV for our signal hypothesis) and the spin of the parent species (vector for background, or scalar for signal) in order to improve discrimination.
This talk presents results of searches for supersymmetry in events with photons. The final states considered are particularly motivated by generalized models of gauge-mediated supersymmetry breaking with a gravitino as the lightest supersymmetric particle. The data samples are recorded with the CMS detector at a center-of-mass energy of 13TeV. Results are interpreted in various models.
R-parity violation introduces many viable signatures to the search for supersymmetry at the LHC. Strongly interacting resonances and lightest supersymmetric particles may decay into many leptons or jets with or without missing transverse momentum. Several supersymmetric models also predict massive long-lived supersymmetric particles. Such particles may be detected through abnormal specific energy loss, appearing or disappearing tracks, displaced vertices, long time-of-flight or late calorimetric energy deposits. The talk presents recent results from searches of supersymmetry in resonance production, R-parity violating signatures and events with long-lived particles with the ATLAS detector.
This project explores limits on a baryon number violating R-parity-violating (RPV) extension of the s-channel production of top squarks, examining it's R-parity-conserving decay into a bottom quark, a lepton, and missing energy. Using Monte Carlo simulations I calculate upper bounds for the RPV parameter $\lambda_{ijk}^{''}$ for a range of top squark masses that would allow for it's existence.
As conventional dark matter scenarios have been probed extensively so far, the physics of a light dark matter charged under a new gauge group (dark gauge group) becomes one of new research avenues in many theoretical and experimental studies. We examine properties of a dark photon showering, the radiation process of light gauge bosons from energetic dark matter particles produced at the Large Hadron Collider (LHC). This showering process provides different signatures at the LHC depending on the property of dark matter under the dark gauge group. We show that the LHC experiment can identify the chirality of a dark matter, which leads to understanding the mass origin of particles in the dark sector.
Dark shower is a generic feature of the Hidden Valley (HV) models. It has interesting implications on collider studies on Neutral Naturalness models. Bound states in the hidden sector are produced with a high multiplicity, low masses, and long lifetimes. A collider search of such signals requires good vertex resolution, low energy threshold, as well as a good particle id to veto the background. We show that the LHCb provides an ideal environment to study HV models. Further, we compare the sensitivities at the LHCb with those at the ATLAS/CMS.
We revisit constraints on dark photons with masses below ∼ 100 MeV from the observations of Supernova 1987A. If dark photons are produced in sufficient quantity, they reduce the amount of energy emitted in the form of neutrinos, in conflict with observations. For the first time, we include the effects of finite temperature and density on the kinetic-mixing parameter, ε, in this environment. This causes the constraints on ε to weaken with the dark- photon mass below ∼ 15 MeV. For large-enough values of ε, it is well known that dark photons can be reabsorbed within the supernova. Since the rates of reabsorption processes decrease as the dark-photon energy increases, we point out that dark photons with energies above the Wien peak can escape without scattering, contributing more to energy loss than is possible assuming a blackbody spectrum. Furthermore, we estimate the systematic uncertainties on the cooling bounds by deriving constraints assuming one analytic and four different simulated temperature and density profiles of the proto-neutron star. Finally, we estimate also the systematic uncertainty on the bound by varying the distance across which dark photons must propagate from their point of production to be able to affect the star. This work clarifies the bounds from SN1987A on the dark-photon parameter space.
In this talk I discuss unappreciated phenomenological consequences of classes of models with new light vector bosons coupled to anomalous currents of Standard Model fermions. Such couplings result in certain process rates growing quadratically with energy. Focusing on this class of constraints I derive new limits that are significantly stronger than in the previous literature for a wide variety of models, and rule out a number of phenomenologically-motivated proposals. As popular examples I focus on the new constraints on the gauging baryon number and on gauging axial number.
I will describe the landscape of constraints on MeV-GeV scale, hidden U(1) forces with nonzero axial-vector couplings to Standard Model fermions. While the purely vector-coupled dark photon, which may arise from kinetic mixing, is a well-motivated scenario, several MeV-scale anomalies motivate a theory with axial couplings which can be UV-completed consistent with Standard Model gauge invariance. I will present a representative renormalizable, UV-complete model of a dark photon with adjustable axial and vector couplings, discuss its general features, and show how some UV constraints may be relaxed in a model with nonrenormalizable Yukawa couplings at the expense of fine-tuning. I will survey the existing parameter space and projected reach of planned experiments, briefly commenting on the relevance of the allowed parameter space to low-energy anomalies in pi^0 and 8-Be* decay.
Axion stars are condensed states of large numbers of axion particles, bound by self-gravitation and quantum self-interactions. The mass of weakly bound axion stars is limited by gravitational stability, with condensates exceeding the maximum mass subject to collapse. During the collapse process, the axion density increases and higher-order self-interactions become increasingly relevant. By taking these terms into account, we provide evidence that in spite of a leading attractive interaction, collapsing axion stars stabilize in a dense state which is larger than its Schwarzschild radius, and so do not form black holes. During the last moments of collapse, number changing processes take place with a very large rate, processes in which individual relativistic axions are emitted from the axion star which escape from galaxies and galaxy clusters. Finally, if axion stars are a significant fraction of cold dark matter, then frequent collisions with each other or with ordinary stars could catalyze this collapse process as well.
The number of nonrelativistic axions can be changed by inelastic reactions that produce relativistic axions or photons. Any even number of nonrelativistic axions can scatter inelastically into two relativistic axions. Any odd number of axions can annihilate into two photons. This reaction produces a monochromatic radio-frequency signal at an odd-integer harmonic of the fundamental frequency set by the axion mass. The loss rates of axions from axion stars through these inelastic relations are calculated using the framework of a nonrelativistic effective field theory. Odd-integer harmonics of a fundamental radio-frequency signal provide a unique signature for collapsing axion stars or any dense configuration of axions.
We argue that the study of rare Higgs decays in the high-luminosity run at the LHC can probe axions and axion-like particles (ALPs) in a wide range of parameter space, which is otherwise inaccessible to experimental searches. If the ALP decays predominantly into photons, our strategy covers the current “gap” in the mass range between 1 MeV and 60 GeV down to photon- axion coupling as small as 10^−6/TeV. An ALP in this parameter range can explain the anomalous magnetic moment of the muon and is consistent with electroweak precisions tests and flavour constraints. In our analysis we consider the most general effective Lagrangian for a spin-0 particle protected by a shift symmetry, motivated by many extensions of the Standard Model with a spontaneously broken global symmetry.
One simple proposal to explain observed anomalies in the small-scale structure of the universe is that dark matter self-interacts. In that spirit, we consider a model of non-abelian, non-confining, gauge boson dark matter that self-interacts through a light vector mediator. The dark sector consists of an SU(2) Yang-Mills theory that is twice-higgsed so that the physical low-energy spectrum includes two heavy, dark-charged vectors and a light dark vector mediator. Perturbative unitarity then puts upper limits on the radial higgs masses, leading to potentially interesting phenomenology. Discussion will center on the generation of the dark sector mass spectrum, its consequences and constraints, and how the model relates to the self-interacting dark matter paradigm.
The discovery of a Higgs boson at the Large Hadron Collider (LHC) motivates searches for physics beyond the Standard Model (SM) in channels involving coupling to the Higgs boson. A search for a massive resonance decaying into a standard model Higgs boson (h) and a W or Z boson or two a standard model Higgs bosons is performed. Final states with different number of leptons and where the Higgs decays into a b-quark pair are studied using different jet reconstruction techniques which are complementary in their acceptance for low and high mass transverse momentum. This talk summarizes ATLAS searches for diboson resonances including at least one H bosons in the final state with LHC Run 2 data.
Beyond the standard model theories like Extra-Dimensions and Composite Higgs scenarios predict the existence of very heavy resonances compatible with a spin 0 (Radion),spin 1 (W’, Z’) and spin 2 (Graviton) particle with large branching fractions in pairs of standard model bosons and negligible branching fractions to light fermions. We present an overview of searches for new physics containing W, Z or H bosons in the final state, using proton-proton collision data collected with the CMS detector at the CERN LHC. Many results use novel analysis techniques to identify and reconstruct highly boosted final states that are created in these topologies. These techniques provide increased sensitivity to new high-mass particles over traditional search methods.
Many extensions to the Standard Model predicts new particles decaying into
two bosons (WW, WZ, ZZ, Zgamma) making these important signatures in the
search for new physics. Searches for such diboson resonances have been
performed in final states with different numbers of leptons, photons and
jets where new jet substructure techniques to disentangle the hadronic
decay products in highly boosted configuration are being used. This talk
summarizes ATLAS searches for diboson resonances with LHC Run 2 data
collected in 2015 and 2016.
The observation of a new resonance in the invariant mass spectrum of two or more objects would be a clear signal for the presence of new physics. Resonance searches in a multitude of final states are therefore a key component of the search strategy for new phenomena at the LHC. In this talk, results from searches in final states containing leptons, photons, and jets performed with the CMS detector will be presented.
When an excess appears in LHC data, we should compare the results with broad classes of models, to get an immediate sense of which kinds of BSM theories could conceivably be relevant. Often, the new physics is likely to be an s-channel resonance. In this case, a simplified model of the resonance can translate an estimated signal cross section into bounds on the product of the dominant production and decay branching ratios. This quickly reveals whether a given class of models could possibly produce a signal of the required size at the LHC. This talk will outline a general framework and show how it operates for resonances of varying widths and with different numbers of production and decay modes. It will also discuss applications to cases of experimental interest, including resonances decaying to di-bosons, di-leptons, or di-jets. If the LHC experiments start reporting searches for BSM resonances in terms of the simplified limits variable $\zeta$ defined here, the community will home in more quickly on the models most likely to explain any observed excess.
In this talk we show that a study of the jet energy correlation functions provides a useful handle to characterize the properties (e.g. spin and color charge) of light resonances which decay only to jets.
Experiments at the LHC may discover a dijet resonance unpredicted by the Standard Model and therefore indicative of Beyond the Standard Model (BSM) physics. In this case, physicists would wonder: what BSM theories are consistent with the unexpected resonance? We examine models featuring a ``leptophobic graviton''--a phenomenological spin-2 color-singlet particle with color-exclusive couplings--and assess the possibility of their discovery in the dijet channel as s-channel resonances. We include a tree-level partial wave unitarity analysis as a phase space constraint. We also apply the color discriminant variable, a unitless combination of quantities (production cross-section, total decay width, and invariant mass) that can be quickly measured after the discovery of a dijet resonance.
We present the NLO QCD corrections to the pair production of heavy
vector color octets in Proton-Proton collisions, as they appear in various
new physics models like Universal Extra Dimensions. To this end we construct
a two-sided Coloron model exhibiting all relevant features while retaining renormalizability without sensitivity to the unknown UV completion of the models. In this framework, we compute the full order $\alpha_s$ corrections to the parton level cross section.
We describe the technical implementation of the calculation in some detail, with some focus on the treatment of IR divergencies.
In this paper, we explore the discriminatory power of the matrix element method in constraining the $L_\mu-L_\tau$ model at the LHC. The $Z'$ boson associated with the spontaneously broken $U(1)_{L_\mu-L_\tau}$ symmetry only interacts with the second and third generation of leptons, and is thus difficult to produce at the LHC. We argue that the best channels for discovering this $Z'$ are in $Z \to 4\mu$ and $2\mu+$MET. Both these channels have a large number of independent observables, which strongly motivates the usage of a multivariate technique. The matrix element method (MEM) is a multivariate analysis that uses the squared matrix element $|\mathcal{M}|^2$ to quantify the likelihood of the testing hypotheses. As the computation of the $|\mathcal{M}|^2$ requires knowing the initial and final state momenta and the model parameters, it is not commonly used in new physics searches. While conventionally new parameters are estimated by maximizing the likelihood of the signal with respect to the background, we outline scenarios in which this process is (in)effective. We illustrate that the new parameters can be determined by studying the $|\mathcal{M}|^2$ distributions, and even if our estimation is off, we may gain better sensitivity than cut-and-count methods. Additionally, unlike conventional MEM techniques that integrate over unknown momenta in processes with MET, we may estimate these momenta, depending on the process topology. This procedure, which we refer to as the ``modified squared matrix element", is computationally much faster than the canonical matrix element method, but also possibly less effective in the signal-background discrimination. Using MEM, we can improve our sensitivity by about an order of magnitude compared with the cut-and-count method for the same amount of data.
In 2010 the proton charge radius was extracted for the first time from muonic hydrogen, a bound state of a muon and a proton. The value obtained was five standard deviations away from the regular hydrogen extraction. Taken at face value, this might be an indication of a new force in nature coupling to muons, but not to electrons. It also forces to reexamine our understanding of the structure of the proton.
In this talk I will describe an ongoing theoretical research effort that seeks to address and resolve this "proton radius puzzle". In particular, I will present a reevaluation of the proton structure effects, correcting 40 years of such calculations, and the development of new effective field theoretical tools that would allow to directly connect muonic hydrogen and muon-proton scattering.
The production of jets and prompt isolated photons at hadron colliders provides a stringent
test of perturbative QCD at the highest energies. These processes can
also be used to constrain the proton structure.
Recent measurements obtained using data collected by the ATLAS
detector at a center-of-mass energy of 8 TeV and 13 TeV will be
presented. These include the measurements of the inclusive jet and multi-jet
production cross-section as well as measurements of the
cross-section of inclusive prompt photon and
di-photon production. The study of the dynamics of isolated photon plus
jet production in proton-proton collisions will also be discussed.
All results are compared with state-of-the-art theory predictions at NLO in pQCD,
interfaced with different parton distribution functions.
Finally, a determination of the strong coupling constant based on the
measurement of the transverse energy–energy
correlation function and its associated azimuthal asymmetry in events
with high transverse momentum jets will be presented.
We analyze the recent LHCb measurement of the distribution of the fraction of the transverse momentum, $z(J/\psi)$, carried by the $J/\psi$ within a jet. LHCb data is compared to analytic calculations using the fragmenting jet function
(FJF) formalism for studying $J/\psi$ in jets. Logarithms in the FJFs are resummed using DGLAP evolution. We also convolve hard QCD partonic cross sections, showered with PYTHIA, with leading order Non-Relativistic Quantum Chromodynamics (NRQCD)
fragmentation functions and obtain consistent results. Both approaches use Madgraph to calculate the hard process that creates the jet initiating parton. These calculations give reasonable agreement with the $z(J/\psi)$ distribution that
was shown to be poorly described by default PYTHIA simulations in the LHCb paper. We compare our predictions for the $J/\psi$ distribution using various extractions of nonperturbative NRQCD long-distance matrix elements (LDMEs) in the literature. NRQCD calculations agree with LHCb data better than default PYTHIA regardless of which fit to the LDMEs is used. LDMEs from fits that focus exclusively on high transverse momentum data from colliders are in good agreement with the LHCb measurement.
Measurements of the vector boson production in $pp$ collisions at $\textbf{LHC}$ form important part of physics programme of the $\textbf{ATLAS}$ Collaboration. More than 50 publications dealing with this topic have been published up to now. All aspects of W/Z physics studied at hadron colliders are covered. Predictions of Standard model are usually tested at least at NLO accuracy, NNLO becomes a standard in the more recent publications. Majority of publications use $\textbf{Run 1}$ data, but the first analyses based on $pp$ collisions at $\sqrt{s}=13$ $TeV$ collected during $\textbf{Run 2}$ period were published recently.
Selection of recent results is presented and future perspectives are described.
Measurements of the cross sections of the production of two and three electroweak gauge bosons at the LHC constitute stringent tests of the electroweak sector of the Standard Model and provide a model-independent means to search for new physics at the TeV scale.
The ATLAS collaboration has performed new measurements of integrated and differential cross sections of the production of heavy di-boson pairs in fully-leptonic and semi-leptonic final states at centre-of-mass energies of 8 and 13 TeV. We present in particular new measurements of WW, WZ and Z+photon cross sections in semi-leptonic or hadronic decays using standard or boosted technologies and new measurements of the inclusive and differential ZZ cross section at 13 TeV in various decay modes.
In addition, the ATLAS collaboration has recently searched for the production of three W bosons or of a W boson and a photon together with a Z or W boson at a center of mass energy of 8 TeV. Moreover, the electroweak production in vector boson fusion of single W and Z bosons with two jets at high invariant mass at centre-of-mass energies of 7, 8 and 13 TeV are studied in different phase space regions. All results are compared to state-of-the art theory predictions and have been used to constrain anomalous quartic gauge couplings.
We present the status of the nCTEQ15 global analysis of nuclear parton distribution functions (nPDFs). In this presentation we briefly discuss the framework of our analysis and concentrate on the comparison of our results with LHC data. Additionally we show a first estimate of the impact of the LHC pPb W/Z boson production data on the presented nCTEQ15 PDFs.
Precision physics at the HL-LHC will require novel techniques to distinguish hard QCD from pileup and beam jets (e.g. the identification of hadronic $W^+$ decay for electroweak measurements or boosted top tagging). One scheme is to identify the signature of QCD radiation inside of jets. The high particle-multiplicity of LHC multijets permits fine-grained investigation of the QCD radiation spectrum via $N$-point correlation functions. But even with a relatively simple example
-- the Fox-Wolfram moments at an $e^+ e^-$ collider -- high-frequency aliasing masks any useful information. We propose a general solution to suppress spectral leakage for any spatial correlation function.
H -> J/Psi + gamma is a clean channel for measurement of the coupling between the Higgs boson and the charm quark. We present the result of our calculation of the decay rate of H -> J/Psi + gamma to relative order v^4 in NRQCD with lightcone resummation.
New results for lowering the KK mass scale and for dark matter within the RS model will be presented.
We propose a novel mechanism to generate a collective quartic in composite Higgs models. We are inspired by the original little Higgs idea in which a tree level quartic arises from the dimensional reduction of 6-dimensional gauge theory. To connect to CH models, our model is set in warped 6D (AdS5xS1), deconstructed for simplicity into a two site 5D RS model. The size of the quartic is controlled by the ratio of the S1 and AdS radii. This leads to an interesting dense spectrum of KK states. In the presence of our independent tree level quartic, the tuning in Composite Higgs model is reduced by a factor of 2-3.
Non-QCD like confining gauge theories promise to be potential UV completions for the Standard Model Electroweak sector, which do not suffer from fine tuning problems. In these scenarios, the Higgs boson would be a composite particle that is kept lighter than other composites by the dynamics of the gauge theory. To determine the viability of this scenario, we have developed an effective-field-theory (EFT) framework to analyze data from lattice simulations of a large class of confining gauge theories. Simulations of these theories, for which the light fermion count is not far below the critical value for transition to infrared conformal behavior, have indicated the presence of a remarkably light singlet scalar particle, which in our EFT framework is interpreted as a dilaton. In this talk, I will explain the essential features of this framework and discuss results obtained applying this framework to lattice data for SU(3) gauge theory with 8 fermion flavors.
In recent years, many numerical investigations of confining Yang Mills gauge theories near the edge of the conformal window
have been carried out using lattice gauge theory techniques. These studies have revealed that the spectrum of hadrons in nearly conformal gauge theories differs significantly from the QCD spectrum. In particular, a light singlet scalar appears
in the spectrum which is nearly degenerate with the PNGBs. This state is a viable candidate for a composite Higgs boson. I report on an investigation which uses both numerical lattice calculations and EFT techniques to determine the correct effective description of nearly conformal gauge theories. I assess a conjecture that the low-lying states are decribed by a linear sigma model.
Warped higher-dimensional compactifications with “bulk” standard model, or their AdS/CFT dual as the purely 4D scenario of Higgs compositeness and partial compositeness, offer an elegant approach to resolving the electroweak hierarchy problem as well as the origins of flavor structure. However, low-energy electroweak/flavor/CP constraints and the absence of non-standard physics at LHC suggest that a “little hierarchy problem” remains, and that the new physics underlying naturalness may lie out of LHC reach. In this talk, assuming this to be the case, I will show that there is a simple and natural extension of the minimal warped model in the Randall-Sundrum framework, in which matter, gauge and gravitational fields propagate modestly different degrees into the IR of the warped dimension, resulting in rich and striking consequences for the LHC (and beyond). The LHC-accessible part of the new physics is AdS/CFT dual to the mechanism of “vectorlike confinement”, with TeV-scale Kaluza-Klein excitations of the gauge and gravitational fields dual to spin-0,1,2 composites. Unlike the minimal warped model, these low-lying excitations have predominantly flavor-blind and flavor/CP-safe interactions with the standard model. Remarkably, this scenario also predicts small deviations from flavor-blindness originating from virtual effects of Higgs/top compositeness at O(10)TeV, with subdominant resonance decays into Higgs/top-rich final states, giving the LHC an early “preview” of the nature of the resolution of the hierarchy problem. Discoveries of this type at LHC Run 2 would thereby anticipate (and set a target for) even more explicit explorations of Higgs compositeness at a 100 TeV collider, or for next-generation flavor tests.
We proposed a natural generalization of standard Randall-Sundrum model, which can address both hierarchy problem and flavor problem, and also give interesting and new signals accessible at LHC. Kaluza-Klein gauge bosons in this model could have significant couplings to the corresponding SM gauge boson and radion. Radion has dominant decay channels to pairs of SM gauge bosons. The cascade decays of heavy gauge bosons render signals containing three SM gauge bosons. The crucial feature of such signals is a double resonance corresponding to the heavy gauge boson and radion respectively. We show that various signal channels have $\sim 3\sigma$ significance at 14TeV LHC with 300fb$^{-1}$.
Abstract: We study the collider signals in a recently proposed RS like scenario with 3 or more branes. This scenario can address both flavor and hierarchy problems and leads to new and interesting signals that are accessible at LHC. I will focus on the 3 brane case when the primary signal involves three EW gauge bosons in the final state. A robust feature of decays in this scenario is the presence of a three body invariant mass peak, as well as another two body invariant mass peak in its constituents. This feature is a powerful discriminant, and can lead to significant significance at LHC14 with 300/fb data in various channels.
In this talk, I discuss the early-universe cosmology of a Kaluza-Klein (KK) tower of scalar fields in the presence of a mass-generating phase transition. I focus on the time-development of the total tower energy density as well as its distribution across the different KK modes, and find that both of these features are extremely sensitive to the details of the phase transition and can behave in a variety of ways significant for late-time cosmology. I also apply this machinery to the example of an axion-like field in the bulk, tracing the flow of the individual KK energy densities over an enlarged axion parameter space that extends beyond those accessible to standard treatments. An important by-product of this analysis is the development of an alternate "UV-based" effective truncation of KK theories which has a number of interesting theoretical properties that distinguish it from the more traditional "IR-based" truncation typically used in the extra-dimension literature. [Based on arXiv:1612.08950 with Keith Dienes and Brooks Thomas.]
We present results of searches for massive vector-like quark partners using proton-proton collision data collected with the CMS detector at the CERN LHC at a center-of-mass energy of 13 TeV. These fourth-generation quarks are postulated to solve the Hierarchy problem and stabilize the Higgs mass, while escaping constraints on the Higgs cross section measurement. The vector-like quark can be produced singly or in pairs and their decays result in a variety of final states containing top and bottom quarks, as well as gauge and Higgs bosons. We search using several categories of reconstructed objects from multi-leptonic to fully hadronic final states. we set exclusion limits on both the vector-like quark mass and cross sections for combinations of the vector-like quark branching ratios.
Vector like quarks appear in many theories beyond the Standard Model as a
way to cancel the mass divergence for the Higgs boson. The current status
of the ATLAS searches for the production of vector like quarks will be
reviewed for proton-proton collisions at 13 TeV. This presentation will
address the analysis techniques, in particular the selection criteria, the
background modeling and the related experimental uncertainties. The
phenomenological implications of the obtained results will also be
discussed.
Higgs boson pair production in the standard model is a rare process, with rates beyond the reach of the currently collected LHC data. The cross section can however be appreciably modified by new physics effects, in particular when the theory contains vector-like quarks, so that di-Higgs boson production could be detectable at the LHC within current data.
We use a phenomenological model containing vector-like quarks to study di-Higgs boson production at the LHC, including next-to-leading-order QCD corrections, and focus on all possible production modes allowed by the new quarks. We in particular show the relevance of higher-order corrections at high vector-like quark masses. We consider the decay of the di-Higgs boson system into two pairs of bottom quarks and demonstrate that the existing Run II ATLAS and CMS analyses could be already sensitive to such a model. We further show that there is a possibility of distinguishing among the various di-Higgs boson production mechanisms by exploiting the kinematic properties of the different production modes.
If the standard model Higgs boson were much heavier, it would appear as
a broad resonance since its decay into a pair of longitudinally polarized gauge bosons is highly enhanced. We study whether the same enhancement happens at loop level in a simple extension of the standard model with a singlet scalar boson S. In order to focus on the loop effects, S is assumed to have no interaction at tree level with the standard model particles. The singlet scalar S is linked to the standard model world radiatively by vector-like quarks running in the loop. We introduce three vector-like quark multiplets, an SU(2)L doublet, an up-type singlet, and a down-type singlet. There are two kinds of loop effects in the S phenomenology, the mixing with the Higgs boson and the radiative decays into
hh, WW, ZZ, gg, and through the triangle loops. We show that the crucial condition for enhancing loop effects including the longitudinal polarization enhancement is the large mass differences among vector-like quarks. The current LHC constraints on S from the heavy scalar searches and the Higgs precision data are shown to be very significant.
Many extensions of the Standard Model that address open issues such as dark matter and baryogenesis require long-lived particles that decay at macroscopic distances and often result in non-conventional signatures in the detector. The broad class of long-lived phenomena presents rich discovery opportunities for the LHC. In this talk I will provide an overview of the searches for long-lived particles at the CMS experiment exploring the final state signatures involving displaced photons/leptons/jets, disappearing tracks, or stopped particles.
The Model Unspecific Search in CMS (MUSiC) represents an alternative analysis strategy to the wide range of dedicated searched performed with LHC data. Apart from offering a consistent overview of a large portion of the CMS data, the analysis also assists in covering regions not investigated by other analyses. This ensures new phenomena are not overlooked simply because certain sectors of the data have not been considered.
Largely unbiased by BSM theory assumptions, data taken with the CMS experiment are compared to a MC simulation based prediction of the full SM. Hundreds of search channels, so called event classes, are automatically constructed and defined by the composition of final state objects found in each event. A fully automated search algorithm surveys several kinematic distributions in each event class and determines the region which exhibits the strongest deviation between data and SM prediction. Subsequent to a look-elsewhere effect correction, all significance values of the individual event class distributions are aggregated to offer a global overview of the findings.
Following an introduction to the MUSiC strategy, results of the application to lepton-triggered events in data taken at sqrt(s)=8 TeV are presented in this talk. In over 300 different final states good agreement between the measured data and SM MC expectation is found. Sensitivity studies show that the analysis is capable of discovering signatures of specific BSM scenarios or SM processes.
Electroweakly charged fermions carrying a strong but dark self-interaction can be pair produced at the LHC and form a bound state. If the bound state is a vector that carries net electric charge, it can be produced through the Drell-Yan process and decay dominantly into the SM $W^{\pm}$ plus a hidden scalar $\phi$, which later decays into SM $b\bar{b}$ through a Higgs mixing. The collider process exists naturally in the $\lambda$-SUSY or Twin-Higgs models, in which $\phi$ can be the singlet scalar of the $\lambda SH_uH_d$ coupling or a $0^{++}$ glueball generated by the twin-QCD. We study the LHC reach of the charged bound state decay and present bounds both in the simplified model and in the $\lambda$-SUSY and Twin-Higgs models.
Inflection-point inflation is an interesting possibility to realize a successful slow-roll inflation when inflation is driven by a single scalar field with its value during inflation below the Planck mass ($\phi_I \leq M_{Pl}$). In order for a renormalization group (RG) improved effective $\lambda \phi^4$ potential to develop an inflection-point, the running quartic coupling $\lambda(\phi)$ must exhibit a minimum with an almost vanishing value in its RG evolution, namely $\lambda(\phi_I) \simeq 0$ and $\beta_{\lambda}(\phi_I) \simeq 0$, where $\beta_{\lambda}$ is the beta-function of the quartic coupling. We consider the inflection-point inflation in the context of the minimal U(1)$_X$ extended Standard Model (SM), a generalization of the minimal U(1)$_{B-L}$ model,where the U(1)$_X$ symmetry is realized as a linear combination of the SM U(1)$_Y$ and the U(1)$_{B-L}$ gauge symmetries.We identify the U(1)$_X$ Higgs field with the inflaton field. For a successful inflection-point inflation to be consistent with the current cosmological observations, the mass ratios among the U(1)$_X$ gauge boson, the right-handed neutrinos, and the U(1)$_X$ Higgs boson are fixed. We first consider the $B-L$ limit with the gauge boson mass less than $1$ TeV. We find that the scenario can be tested in the future collider experiments such as the High-Luminosity LHC and the SHiP experiments. On the other extreme, we consider the scenario such that the U(1)$_X$ gauge symmetry is mostly oriented towards the SM U(1)$_Y$ direction and investigate a consistency between the inflationary predictions and the latest LHC Run-2 results on the search for a narrow resonance with the di-lepton final state.
Several theories beyond the Standard Model, like the EWS or 2HDM models, predict the existence of high mass neutral or charged Higgs particles. In this presentation the latest ATLAS results on searches for these particles will be discussed.
The strong phase from QCD could play important role in (B)SM heavy particle productions at hadron colliders, altering the resonance signatures significantly and providing more physics insights into the underlying physics. I will discuss the strong phase in Higgs phenomenology and the new windows opened up for BSM physics.
We analyze the hVV (V = W, Z) vertex in a model independent way using
Vh production. To that end, we consider possible corrections to the Standard Model Higgs Lagrangian, in the form of higher dimensional operators which parametrize the effects of new physics. In our analysis, we pay special attention to linear observables that can be used to probe CP violation in the same. By considering the associated production of a Higgs boson with a vector boson (W or Z), we use jet substructure methods to define angular observables which are sensitive to new physics effects, including an asymmetry which is linearly sensitive to the presence of CP odd effects.
We calculate the helicity amplitude of $e^+e^-\to ht\bar{t}$, where the Higgs boson h(125) is assumed to be a CP mixed state with both CP-even and CP-odd components. The amplitudes depend both on the CP violating htt Yukawa coupling and the CP conserving $hZZ$ coupling. We calculate the helicity amplitudes in the tt rest frame, where the initial $e^+e^−$ current and the final Higgs boson have the same three-momentum. CP violating asymmetries appear not only in the azymuthal angle between the $e^+e^−$ to the Higgs production plane and the htt decay plane, which have been studied in the past, but also in the correlated angular distributions of charged leptons from t and t decays. Complete description of the production and decay angular distributions is obtained analytically, and the distributions of CPV observables from final state of top pair decays semileptonically are investigated. We also study the ultimate sensitivity to the CP violating htt coupling at the international linear colliders in its various running scenarios.
In this talk we will review the results on the searches for light beyond the standard model higgs boson states with CMS data.
The current run of the LHC is at full swing. An important task for the experimental and theoretical community is to study in detail the scalar sector of nature, in order to determine whether the Standard Model or a possible extension is realized. In this talk, I will discuss two such extensions, viz., a model with a simple scalar extension as well as a two Higgs doublet model. I will discuss recent constraints on the models parameter space and present benchmarks for the current LHC run
LHC searches with $\tau$ leptons in the final state are always inclusive in missing-energy sources. A signal in the flavor-violating Higgs decay search, $h\to\tau\mu$, could therefore equally well be due to a flavor conserving decay, but with an extended decay topology with additional invisible particles.
In this talk, I demonstrate this with the three-body decay $h\to\tau\mu\varphi$, where $\varphi$ is a flavorful mediator decaying to a dark-sector.
This scenario can give thermal relic dark matter that carries lepton flavor charges, a realistic structure of the charged lepton masses, and explain the anomalous magnetic moment of the muon, $(g-2)\mu$, while simultaneously obey all indirect constraints from flavor-changing neutral currents. Another potentially observable consequence is the broadening of the collinear mass distributions in the $h\to \tau\mu$ searches.
The discovery of a 125 GeV scalar particle, and it subsequent identification with the Higgs bosons of the SM, is one of the greatest accomplishments of high-energy particle physics. However, the discovery of this particle still leaves many open questions. In this talk we would like to understand if the observed 125 GeV Higgs gives mass to all quarks and leptons. We will entertain the idea that the Higgs is not the only source of electroweak symmetry breaking and study the resulting phenomenological implications.
Mini-Review On Non-WIMP dark matter
Recently the well known core/cusp problem in the lambda cold dark matter ($\Lambda$CDM) paradigm is upgraded to the diversity problem in the galaxy rotation curve due to the failure of $\Lambda$CDM to explain the diverse behavior in observed rotation curves, especially for dwarf galaxies. To determine whether self-interacting dark matter (SIDM) framework will help to understand this issue, we follow our previous work and fit 120 galaxy velocity rotation curves from SPARC dataset using SIDM model and only assuming the halo concentration-mass relation predicted by the $\Lambda$CDM model and a fixed value of self-interaction cross section. Our result shows SIDM dramatically improves the ability to fit the rotation curve comparing to CDM. Discrepancy in halo masses corresponding to the same disk mass between result from fitting and expectation from abundance matching may indicate the "too-big-to-fail" problem still exist with SIDM. Radial acceleration relation and baryonic Tully-Fisher relation are closely reproduced though with a bit large reasonable scatter. These results suggest that current SIDM maybe not perfect but demonstrates its great potential to solve and explain small scale issues.
Strongly self-interacting dark matter (SSIDM) was proposed as a candidate which might be able to solve astrophysical problems plaguing collisionless cold dark matter: the cusp-vs-core, the missing satellite and the too-big-to-fail problems. These SSIDM particles can in principle form bound states. In particular, if the SSIDM particles belong to a confining gauge group, the singlet states (similar to the baryons of QCD but whose spin depends on the gauge group), the so-called dark "baryons", can cluster into astronomical compact objects which will be called Dark Astronomical Extreme Compact Objects (DAECO) in this paper. How massive can they be? What are their typical sizes? Depending on the mass of the dark baryon, a DAECO can be as "large" as 33 Earth mass for a 1-TeV dark baryon to 0.3 Earth mass for a 10-TeV dark baryon. These DAECOs are extremely small: 15 cm for the 33-Earth mass DAECO and 1.5 mm for the 0.3-Earth mass one. These planetary-mass-type DAECO’S could be "detected" for using techniques such as the astrometric measurements as applied to the searches for exoplanets. Specifically, one would look for gravitational influences of DAECOS’s on a given star when they come lose to it. The search for DAECO’s, if they exist, would provide a "direct" detection of strongly self-interacting dark matter at an astronomical level, somewhat similar to laboratory direct detection searches through the detection of nuclear recoil. Another possibility is the merger of two clusters of DAECOs with each having a mass ∼ 30 M generating gravitational waves of the types observed by LIGO.
The thermal relic density of dark matter is conventionally set by two-body annihilations. We point out that in many simple models, 3→2 annihilations can play an important role in determining the relic density over a broad range of model parameters. This occurs when the two-body annihilation is kinematically forbidden, but the 3→2 process is allowed; we call this scenario "Not-Forbidden Dark Matter". We illustrate this mechanism for a vector portal dark matter model, showing that for a dark matter mass of mχ ∼ MeV - 10 GeV, 3→2 processes not only lead to the observed relic density, but also imply a self-interaction cross section that can solve the cusp/core problem. This can be accomplished while remaining consistent with stringent CMB constraints on light dark matter, and can potentially be discovered at future direct detection experiments.
The existence of dark matter (DM) in the universe is strong evidence that new physcs beyond the Standard Model is needed to explain relevant phenomenology. As we know little about DM properties, many well-motivated new physics models consider the minimal dark/hidden sector scenario, "forgetting" other members in the hidden sector. Furthermore, DM experiments are designed and results are interpreted in the context of the minimal hidden-sector scenario. In this talk, I will discuss some interesting DM phenomena under non-minimal hidden-sector
framework which would not emerge in the minimal setup and point out that they may alter the existing DM search paradigm and offer a new avenue towards understanding DM phenomenology. This talk will be a prelude to the two talks devoted to discuss 1) Dark Matter "Collider" as a form of DM direct detection experiments and 2) Dark Matter "Transporting" Mechanism to explain cosmic positron excesses reported by satellite-based DM indirect detection experiments.
I will talk about a novel dark matter (DM) detection strategy for the models with non-minimal dark sector. The main ingredients in the underlying DM scenario are a boosted DM particle and a heavier dark sector state. The relativistic DM impinged on target material scatters off inelastically to the heavier state which subsequently decays into DM along with lighter states including visible (Standard Model) particles. The expected signal event, therefore, accompanies a visible signature by the secondary cascade process associated with a recoiling of the target particle, differing from the typical neutrino signal not involving the secondary signature. I will discuss the detection prospects of this DM signal at current and future large volume neutrino detectors such as Super/Hyper Kamiokande and DUNE, as well as future fixed target experiments.
We propose a novel mechanism to accommodate the positron excesses observed by PAMELA and AMS-02 under the dark matter interpretation. Unlike the known approaches of enhancing annihilation/decay strength or local dark matter density nearby the Earth, our proposal makes direct use of dark matter nearby the Galactic Center where it populates most densely in the Galaxy. The key points of this mechanism include dark matter annihilation/decay into intermediary particles with long enough laboratory-frame life time and their "retarded" decay near the Earth to electron-positron pair(s) possibly with other (in)visible particles, not in conflict with various cosmological and astrophysical constraints. We expect that the idea can be readily applicable to various cosmic-ray excesses.
Measurements of the ultra-rare K --> pi nu nu decays represent a stringent
test of the CKM paradigm, probing short distance scales beyond the reach of
the LHC. The main goal of the NA62 experiment at CERN is the measurement of
the K+ --> pi+ nu nu decay rate at 10% precision; the broader physics
programme includes searches for lepton flavour and lepton number violation
in kaon decays at record sensitivity, as well as rare kaon and pion decay
measurements. The NA62 is currently in the middle of the data taking
campaign (2016-2018). Its status, physics reach and recent results,
including new limits on heavy neutral lepton production in kaon decays, are
presented.
New and recent results from the ATLAS programme of studies in EW physics with open beauty are presented, which includes studies of CP violation in the Bs sector and of FCNC in Bd and Bs.
FCNC processes are sensitive of NP contributions, in particular through additional electroweak loop amplitudes. The angular analysis of the decay of Bd -> K* mu mu for a number of angular coefficients are measured as a function of the invariant mass squared of the di-muon system for data collected at 8 TeV. Comparison is made to theoretical predictions, including for the observable P¿5, for which there has been recent tension between theory and experiment.
Three key issues pertaining to the semi-leptonic RD(*) anomalies will be addressed here: 1) How robust are the SM predictions? 2) What are the model-independent collider signature of these anomalies? 3) What are some of the simplest BSM explanations for these?
In answer to 1) latest information from on and off the lattice will be critically examined to question, in particular the reliability of the stated theory error. Reg 2) It will be shown that the semi-leptonic anomalies rigorously imply unavoidable collider signatures that the LHC experimental community should ASAP vigorously pursue to confirm or refute these anomalies. Lastly, but nevertheless of considerable importance, reg 3), is the issue of what interesting, and theoretically well motivated, underlying extensions of the SM that could be responsible for these anomalies assuming they withstand further scrutiny and the test of time.
\begin{abstract}
The confirmation of excess in $R_{D^*}$ at the LHCb is an indication of lepton flavor non-universality. Various different new physics operators and their coupling strengths, which provide a good fit to $R_D$, $R_{D^*}$ and $q^2$ spectra, were identified previously. In this work, we try to find angular observables in $\bar{B} \to D^* \tau \bar{\nu}$ which enable us to distinguish between these new physics operators. We find that $D^*$ polarization fraction $f_L(q^2)$ is a good discriminant of scalar and tensor new physics operators.
The change in $\langle f_L(q^2) \rangle$, induced by scalar and tensor operators, is about three times larger than the expected uncertainty in the upcoming Belle measurement.
The semileptonic decays $B\to D^{(\ast)}\tau\nu$ have received lots of attention recently, due to an observed discrepancy between standard-model predictions and measurements. Experimentally, these processes are challenging due the fast decay of the tau lepton, which is indirectly observed through its decay products. From a theory perspective, the tau lepton is exactly what makes $B\to D^{(\ast)}\tau\nu$ decays interesting: The massive lepton offers the possibility to study its polarization states individually and thereby learn about the details of its production. I will show how to obtain tau properties directly from kinematics of the visible decay products in $\tau\to\pi\nu$, $\tau\to\rho\nu$, and $\tau\to\ell\nu\bar\nu$ decays. These new observables provide us with an analytical framework to fully explore the properties of $B\to D^{(\ast)}\tau\nu$ at BELLE II.
Effective field theories such as Heavy Quark Effective Theory (HQET) and Non Relativistic Quantum Chromo-(Electro-) dynamics NRQCD (NRQED) are indispensable tools for controlling the effects of the strong interaction. The increasing experimental precision requires the knowledge of higher dimensional operators. These operators are important to the evaluation of decay rates of the B-meson. We present a general method that allows for an easy construction of HQET (NRQED and NRQCD) operators that contain two heavy quark (non-relativistic) fields and any number of covariant derivatives. As an application of our method, we give for the first time all such terms in the $1/M^4$ NRQCD Lagrangian, where $M$ is the mass of the spin-half field. We analyze the general dimension-nine spin-independent HQET matrix element, which was not considered so far in the literature, and calculate moments of the leading power shape function up to and including dimension nine HQET operators.
A wide programme of studies in heavy flavour production at the LHC is performed with the ATLAS detector, including charm and beauty hadrons, quarkonia production in both sectors, and associated production J/psi + W, J/psi + Z and J/psi + J/psi.
This talk will cover recent results from ATLAS, including the recent result on prompt J/psi + J/psi, measuring the differential cross-section in several kinematic variables, and a measurement of the fraction of double parton scattering, with comparisons to predictions. The X(3872) production is also studied, as well as correlations in b-bbar production.
The LHCb has reported the observation of a resonancelike structure, the $P_c(4450)$, in the $J/\psi~p$ spectrum.
In our work, we discuss the feasibility of detecting this structure in $J/\psi$ photoproduction, e.g., in the measurement that has recently been approved for the CLAS12 experiment at JLab.
We take into account the experimental resolution effects, and perform a global fit to world $J/\psi$ photoproduction data, predicting that it will be possible to observe a sizable cross section close to the $J/\psi$ production threshold. We present a first estimate of the upper limit for the branching ratio of the $P_c(4450)$ into the $J/\psi~p$ channel, and we study the angular distributions of the differential cross sections. This will shed light on the nature and couplings of the $P_c(4450)$ structure in the future photoproduction experiments.
In SUSY-like models with dark matter candidates, LHC events contain two decay chains, each terminating in an invisible particle, whose true energy and momentum are not measured in the detector. I will review and contrast some recently proposed invariant mass variables which are suitable for such event topologies. Each variable relies on a specific ansatz for the unmeasured individual 4-momenta of the invisible particles in the event.
We critically examine the classic endpoint method for particle mass determination, focusing on di?fficult corners of parameter space, where some of the measurements are not independent, while others are adversely a?ected by the experimental resolution.In such scenarios, mass di?erences can be measured relatively well, but the overall mass scale remains poorly constrained. Using the example of a standard SUSY decay chain we demonstrate that sensitivity to the remaining mass scale parameter can be recovered by measuring the two-dimensional kinematical boundary in the relevant three-dimensional phase space of invariant masses squared. We develop an algorithm for detecting this boundary, which uses the geometric properties of the Voronoi tessellation of the data, and in particular, the relative standard deviation (RSD) of the volumes of the neighbors for each Voronoi cell in the tessellation. We propose a new observable, which is the average RSD per unit area, calculated over the hypothesized boundary. We show that the location of the ??function maximum correlates very well with the true values of the new particle masses. Our approach represents the natural extension of the one-dimensional kinematic endpoint method to the relevant three dimensions of invariant mass phase space.
We investigate the solvability of the event kinematics in missing energy events at hadron colliders, as a function of the particle mass ansatz. To be specific, we reconstruct the neutrino momenta in dilepton $t\bar{t}$-events, without assuming prior knowledge of the top, W and neutrino masses. We identify a class of events, which we call extreme events, with the property that the boundary of their allowed region in mass parameter space passes through the true mass point. We show that the collection of such extremeness boundaries is focused on the true values of the mass parameters and can be effectively used for mass determination. We derive a kinematic variable which allows us to recognize a given event as extreme.
Tools from information geometry can be used to understand and optimize LHC measurements. Our approach is based on the Fisher information, which encodes the maximum precision with which theory parameters can be measured in a given experiment. We show how the Fisher information in LHC processes can be calculated, and demonstrate how information geometry lets us improve event selections, determine the most powerful observables, and compare the power of modern multivariate techniques to that of traditional histogram-based analyses.
As discussed in the previous talk, tools from information geometry can be used to understand and optimize LHC measurements. As an example, we calculate the maximum sensitivity of Higgs measurements to the dimension-6 operators of a Higgs effective field theory. The Fisher Information then encodes the maximum precision with which the theory parameters - in this case the Wilson coefficients - can be measured. In particular we consider Higgs production in weak boson fusion with decays into tau pairs and four leptons. We find that crucial information comes from the high-energy tails as well as from angular correlations between jets, while the decay kinematics hardly adds any information. Tight cuts on the rapidity separation of the tagging jets throw away a large amount of discrimination power. While conventional analyses can probe new physics scales around 900 GeV in the early phase of LHC Run II, multivariate analyses have the potential to significantly enhance the sensitivity up to 1.2 TeV. We further discuss Higgs production in association with a single top quark.
We introduce a new scale-invariant jet clustering algorithm which does not impose a fixed cone size on the event. The proposed construction maintains excellent object discrimination for very collimated partonic systems. Nevertheless, it is able to asymptotically recover favorable behaviors of the standard anti-KT algorithm. Additionally, it is intrinsically suitable for the tagging of highly boosted objects. Because of these properties, this algorithm may prove to be useful for the continuing study of jet substructure.
The Global and Modular Beyond-the-Standard Model Inference Tool (GAMBIT)
is an open-source tool for performing global fits in generic Beyond the Standard Model theories. GAMBIT is the amalgamation of frontline scanner algorithms, advanced calculations of physical observables and likelihoods, and a flexible and powerful interface with the user and external codes. Due to the deep modularity of the code, GAMBIT allows the addition of user-made models, observables and scanners in a highly simplistic manner, as well as the usage of any extenal backend tool, easily embedded and run in unison. In this talk I will introduce the main features of GAMBIT, briefly describing the core and internal structure of the code. I will also present the first preliminary results obtained with GAMBIT regarding global fits on a CMSSM and a Singlet Dark Matter model. Lastly I will discuss the plans for future extensions and improvements of the code, along with the steps made towards expanding the set of models covered and the inclusion of new physics sectors.
Renormalization Group Equations for an arbitrary gauge field theory have been known at two-loop for about 30 years. Deriving them by hand for a specific model is a very tedious task prone to errors. In order to automate this process, we released in 2014 a Python program called PyR@TE that automatically derived the RGEs for a given Lagrangian (non-SUSY).
Recently, we published the second version of this program that greatly extends the capabilities of the first version. In particular, models involving kinetic mixing are now fully supported at two-loop, and a dedicated group theory library has been developed in order to cover generic group and irreducible representations.
In this talk, an overview of PyR@TE will be given with a strong emphasis on the new capabilities.
We will describe the diagonalization of the Hamiltonian of $\lambda\phi^4$ theory. We will focus on scattering states far above the vacuum and will consider the inner product between these scattering states as the first step towards the calculation of the scattering amplitudes. We will show some of our preliminary results along with their comparison with perturbation theory.
We study 1+1 dimensional $\phi^4$ theory using the recently proposed method of conformal truncation. Starting in the UV CFT of free field theory, we construct a complete basis of states with definite conformal Casimir, $\mathcal{C}$. We use these states to express the Hamiltonian of the full interacting theory in lightcone quantization. After truncating to states with $\mathcal{C} \leq \mathcal{C}_{\max}$, we numerically diagonalize the Hamiltonian at strong coupling and study the IR dynamics. In particular, we determine the critical value of the coupling, at which the mass gap closes, and compute non-perturbative spectral densities of local operators, which are equivalent to real-time, infinite-volume correlation functions. Near the critical point, the resulting spectral densities reproduce those of the 2D Ising model.
A Non-Local quantum field theory extension of QED is considered. Gauge invariance is checked to 1-loop order and the gauge coupling running is shown to be UV-Insensitive. In the future, extending this model to incorporate other fields could provide an avenue for remedying the Higgs vacuum instability problem.
Astrophysical black hole candidates, although long thought to have a horizon, could be horizonless ultra-compact objects. This intriguing possibility is motivated by the black hole information paradox and a plausible fundamental connection with quantum gravity. Asymptotically free quadratic gravity is considered here as the UV completion of general relativity. We find that sufficiently dense matter produces a novel horizonless configuration, the 2-2-hole, which closely matches the exterior Schwarzschild solution down to about a Planck proper length of the would-be horizon and has an interesting interior. In the era of gravitational-wave astronomy, the quantum gravity corrections around the black hole horizon lead to distinctive features that could hopefully be probed in the near future.
Hoop conjecture allows the formation of black holes through the collision of particles. We consider a system consisting of massless bosons at a finite temperature and analyze the formation of black holes using hoop conjecture in an expanding universe in the slow expansion limit (HRS < <1). We found that the black hole number density increases rapidly with the temperature of background radiation and decreases due to the expansion of space-time via Hubble constant. We evolved the system, incorporating the Hawking evaporation and the accretion of matter by black holes and found that black holes and radiation cannot coexist in stable equilibrium. In an expanding universe, unlike flat space-time, black hole number density never dominates over the number density of background radiation at any temperature below Planck temperature. Our study sheds light on the formation of primordial black holes in the early universe.
There is no guarantee that the violation of lepton number, assuming it exists, will primarily manifest itself in neutrinoless double beta decay. Lepton-number violation and lepton-flavor violation may be related, and one complementary observable to double beta decay is muon-to-positron conversion. In this talk, I will discuss an effective field theory approach to estimating muon-to-positron conversion rates for dimension-five, -seven, and -nine operators. I will also discuss the relationship between these lepton-number-violating processes and the Majorana neutrino masses the new operators generate.
A plethora of ultraviolet completions of the Standard Model have extra U(1) gauge symmetries. In general, the associated massive $Z^\prime$ gauge boson can mediate flavor-changing neutral current processes at tree level. We consider a situation where the $Z^\prime$ boson couples solely via flavor-changing interactions to quarks and leptons. In this scenario the model parameter space is, in general, quite well constrained by existing flavor bounds. However, we argue that cancellation effects shelter islands in parameter space from strong flavor constraints and that these can be probed by multipurpose collider experiments like ATLAS or CMS as well as LHCb in upcoming runs at the LHC. In still allowed regions of parameter space these scenarios may help to explain the current tension between theory and experiment of $(g-2)_\mu$ as well as a small anomaly in $\tau$ decays.
We argue that lepton flavor violating (LFV) decays $M \to \ell_1 \overline \ell_2$ of quarkonium and heavy quark meson states $M$ with different quantum numbers could be used to put constraints on the Wilson coefficients of effective operators describing LFV interactions at low energy scales. We note that the restricted kinematics of the two-body decay of quarkonium or a heavy quark meson allows us to select operators with particular quantum numbers, significantly reducing the reliance on the single operator dominance assumption that is prevalent in constraining parameters of the effective LFV Lagrangian. We shall also argue that studies of radiative lepton flavor violating $M \to \gamma \ell_1 \overline \ell_2$ decays could provide important complementary access to those effective operators.
An alternative left-right model of quarks and leptons, where the SU(2)$_R$ lepton doublet $(\nu, l)_R$ is replaced with (n, l)$_R$ so that n$_R$ is not the Dirac mass partner of $\nu_L$,has been known since 1987. Previous versions assumed a global U(1)$_S$ symmetry to allow n to be identified as a dark-matter fermion (scotino). We propose here a gauge extension by the addition of extra fermions to render the model free of gauge anomalies,and just one singlet scalar to break U(1)$_S$. This results in two layers of dark matter,one hidden behind the other.
This is the gauged version of the arXiv:0901.0981, arXiv:1002.0692
Grand Unified Theories (GUTs) are well-motivated extensions of the Standard Model. They represent a theoretically sound approach to explore physics at very high scales given the lack of firm signs of new physics near the electroweak scale. This talk will focus on SO(10)-symmetric models with a two-step symmetry breaking chain, where the only intermediate scale respects the left-right symmetric gauge group SU(3) x SU(2)L x SU(2)_R x U(1){B-L}. We scan through all
possible minimal non-SUSY left-right symmetric models fulfilling the unification condition in an automated way. A group-theoretical top-to-bottom approach is used for the generation of beta functions corresponding to different field contents. The subsequent one-loop RGE analysis provides us with the unknown new-physics scales and couplings. Based on these quantities we show which (and what portion) of the constructed models are excluded when current and future experimental limits on observables such as proton decay, neutron-antineutron oscillations or lepton flavour violation are imposed. Besides the particular restrictions, a number of other interesting remarks on specific types of models can be made.
We propose a simple left-right symmetric model which generates radiative majorana neutrino masses through the Zee mechanism. Its scalar content is composed of the minimal degrees of freedom required for symmetry breaking and mass generation plus a singlet charged higgs which, along with the softly broken left-right symmetry in the yukawa sector, is responsible of the radiative neutrino masses and some lepton flavor violation processes. In this context, neutrino masses are generically light and can give rise to large lepton number violating contributions to rate process such as mu to e gamma or mu to e conversion. We discuss the correlation between the collider constraints and the predictions for such lepton number violating processes, showing the testability of this theory in the near future.
In this talk we discuss the sensitivity of probing light scalars in the Borexino detector, and the possibility of detecting heavy leptons in the SHiP and DUNE experiments.
First we address in detail the sensitivity of the Borexino-SOX conﬁguration in detecting light scalar particles coupled to the SM fermions. Within one year of operations one can achieve an unprecedented sensitivity to the coupling constants of such scalars, probing signiﬁcant parts of parameter space that are not excluded either by the beam dump constraints or astrophysical bounds. These light scalars were proposed to explain the anomaly in the measurements of charge radius of the proton, and such explanation in its simplest form can be definitely tested in our setup.
We then move on to briefly discuss the possibility of utilizing SHiP and DUNE experiments to probe long-lived heavy leptons.
We point out that in generic TeV scale seesaw models for neutrino masses with
local B −L symmetry breaking, the Higgs field breaking the B −L symmetry can leave a physical real scalar field with mass around GeV scale. In the specific case when the B − L symmetry is embedded into the left-right symmetry, low energy flavor constraints necessarily require the light scalar to be long lived, with displaced vertex signals of collimated photon jets at the LHC. Thus, the search for such long-lived light scalar particles provides a new way to probe TeV scale seesaw models for neutrino masses at colliders.
We analyze the collider signatures of the real singlet extension of the Standard Model in regions consistent with a strong first-order electroweak phase transition and a singlet-like scalar heavier than the Standard Model-like Higgs. We study the prospects for observing these processes at the LHC and a future 100 TeV pp collider, focusing particularly on double singlet production. We also discuss correlations between the strength of the electroweak phase transition and other observables at hadron and future lepton colliders. Searches for non-resonant singlet-like scalar pair production at 100 TeV would provide a sensitive probe of the electroweak phase transition in this model, complementing resonant di-Higgs searches and precision measurements.
To probe the electroweak phase transition, cosmologists are looking forward to the next generation of high energy collider experiments, which will likely be electron-positron colliders that sit at the threshold to produce a Z-boson and Higgs boson pair. These Higgs factories will furnish precisions measurements of the Higgs’s couplings to other Standard Model particles. In the talk, I will discuss a few simplified extensions of the Standard Model that include new particles at the electroweak scale, and I will assess how precision measurements of the Higgs-Z-Z coupling, in particular, can be used to deepen our understanding of the electroweak phase transition.
The Higgs potential consists of an unexplored territory in which the electroweak symmetry breaking is triggered, and it is moreover directly related to the nature of the electroweak phase transition. Measuring the Higgs boson trilinear and quartic couplings, or getting equivalently information on the exact shape of the Higgs potential, is therefore an essential task. However, direct measurements beyond the trilinear self-interaction of the Higgs boson is a huge challenge, even for a future proton-proton collision machine expected to operate at a center-of-mass energy of 100 TeV. We present a novel approach to extract model-independent constraints on the triple and quartic Higgs self-coupling by investigating triple Higgs-boson hadroproduction at a center-of-mass energy of 100 TeV, focusing on the $\tau \tau b \bar{b} b \bar{b}$ channel which was previously overlooked due to a supposedly too large background. It is thrown into sharp relief that the assist from a kinematic bounding variable and a boosted configuration ensures a high signal sensitivity. We derive the luminosities that would be required to constrain given deviations from the Standard Model in the Higgs self-interactions, showing for instance that a 2 sensitivity could be achieved for an integrated luminosity of 30 $\rm ab^{-1}$ when Standard Model properties are assumed. Our results, overlayed with trilinear Higgs coupling studies from di-Higgs production, could hence be useful for the design of a future hadronic collider.
We derive the electroweak (EW) collinear splitting functions for the Standard Model, including the massive fermions, gauge bosons and the Higgs boson. We first present the splitting functions in the limit of unbroken SU(2)_L × U(1)_Y and discuss their general features in the collinear and soft-collinear regimes. These are the leading contributions at a splitting scale (k_T) far above the EW scale (v). We then systematically incorporate EW symmetry breaking (EWSB), which leads to the emergence of additional “ultra-collinear” splitting phenomena and naive violations of the Goldstone-boson Equivalence Theorem. We suggest a particularly convenient choice of non-covariant gauge (dubbed “Goldstone Equivalence Gauge”) that disentangles the effects of Goldstone bosons and gauge fields in the presence of EWSB, and allows trivial book-keeping of leading power corrections in v/k_T. We implement a comprehensive, practical EW showering scheme based on these splitting functions using a Sudakov evolution formalism. Novel features in the implementation include a complete accounting of ultra-collinear effects, matching between shower and decay, kinematic back-reaction corrections in multi-stage showers, and mixed-state evolution of neutral bosons (gamma/Z/h) using density-matrices. We employ the EW showering formalism to study a number of important physical processes at O(1-10 TeV) energies. They include (a) electroweak partons in the initial state as the basis for vector-boson-fusion; (b) the emergence of "weak jets" such as those initiated by transverse gauge bosons, with individual splitting probabilities as large as O(35%); (c) EW showers initiated by top quarks, including Higgs bosons in the final state; (d) the occurrence of O(1) interference effects within EW showers involving the neutral bosons; and (e) EW corrections to new physics processes, as illustrated by production of a heavy vector boson (W') and the subsequent showering of its decay products.
In this talk, we discuss the new physics implication of Higgs Precision Measurements at the future electron-positron Higgs factories, including the Chinese proposal CEPC, the European proposal FCC-ee, as well as the Japanese proposal of ILC. We explored two typical types of new physics models: Two Higgs Double Model (2HDM) as an example of weakly coupled BSM scenarios, and composite Higgs Model as an example of strongly coupled BSM scenarios. For 2HDM, we studied both the tree level effects, mainly, the effect caused by the mixture of SM-like Higgs and Non-SM like Higgs in the 125 GeV light Higgs, as well as the loop effects, introduced by the extra Higgses running in the loop. We found that even comparing to HL-LHC with 3000 ${\rm fb}^{-1}$ luminosity, future Higgs factories could narrow the region of $\cos(\beta-\alpha)$ at least a factor of 2 smaller when considering tree level effects only. Considering the loop effects in the alignment limit, the heavy Higgs masses could be constrained to be larger than 500 GeV or better. For composite Higgs Model, we performed a 10-parameter fit to the coefficients of the effective operators. The scale Lambda for the non-renormalizable operators could be constrained to be around 5 TeV or higher.
We present strategies to search for heavy scalars decaying to top quark pairs. The gluon fusion channel is unsatisfactory due to the interference effect with SM background. We propose to use heavy scalar production in association with one or two top quarks. In the framework of type II two Higgs doublet models at low tan_beta(heavy neutral Higgs mainly decaying to top quark pairs), we obtain current limits at the LHC using Run I data at 8TeV and show the potential sensitivity during Run II at 14 TeV. A detailed BDT study is performed for 14 TeV LHC and 100 TeV collider in the future.
A future \sqrt{s} = 100 TeV proton-proton collider will have a remarkable capacity to discover massive new particles and continue exploring weak scale naturalness. In this work we will study its sensitivity to two stop simplified models as further examples of its potential power: pair production of stops that decay to tops or bottoms and higgsinos; stops that are either pair produced or produced together with a gluino and then cascade down through gluinos to the lightest superpartner (LSP). In both simplified models, super-boosted tops or bottoms with transverse momentum of order TeV will be produced abundantly and call for new strategies to identify them. We will apply a set of simple jet observables, including track-based jet mass, mass drop and N -subjettiness, to tag the boosted objects and suppress the Standard Model as well as possible SUSY backgrounds. We will also discuss how to use jet observables to distinguish simplified models with different types of LSPs. The boosted top or bottom tagging strategies developed in this paper could also be used in studies of other physics cases for a 100 TeV collider.
The construction of a photon collider is urged in order to study the properties of the Higgs boson and electroweak symmetry breaking. It has been claimed that the process γγ → QQ ̄(g) could be the major contribution for the background of Higgs production in photon collisions. However, there are also some papers that claim the contribution is not so strong, which means that the photons are interesting in themselves. This researches examines how well we understand resolved photons and their uncertainties.
A largely model-independent probe of dark matter-nucleon interactions is proposed. Accelerated by gravity to relativistic speeds, local dark matter scattering against old neutron stars deposits kinetic energy that heats them to infrared blackbody temperatures. The resulting radiation could be detected by next generation telescopes such as James Webb, the Thirty Meter Telescope and the European Extremely Large Telescope. While underground direct detection searches are not (or poorly) sensitive to dark matter with sub-GeV masses, higher-than-weak-scale masses, scattering below neutrino floors, spin-dependent scattering well below nuclear cross-sections, and inelastic scattering for inter-state transitions exceeding O(100 keV), dark kinetic heating of neutron stars advances these frontiers by orders of magnitude, and should vastly complement these searches. Popular dark matter candidates previously suspected challenging to probe, such as thermal Higgsinos, may be discovered.
A significant part of dark matter could be made of compact objects, such as primordial black holes. In this talk I will discuss how to use Fast Radio Bursts (FRBs) to directly test this hypothesis. FRBs are powerful and short radio emissions emanating from extragalactic sources. A compact component of the dark matter can act as a gravitational lens and create multiple images of a single FRB. Oppositely to strong lensing of quasars, where the angular resolution allows us to resolve the different lensed images, here we use the time delay induced by gravitational lensing to search for lensed FRBs. With one year of data from CHIME/HIRAX, which are under construction, we will be able to detect any compact component of the dark matter down to one part in a hundred, if it is more massive than 20 solar masses.
The direct detection of sub-GeV dark matter (DM) has received increased interest in the last few years. Recent proposals for experimental ideas using DM-electron scattering have opened up previously unexplored, but theoretically well-motivated, regions of parameter space. As these experiments increase their cross-section reach, they will start to become sensitive to astrophysical neutrinos. The coherent scattering of neutrinos can mimic a DM signal, and for experiments without directional sensitivity, is indistinguishable from DM. In this talk, I will present the minimum cross-sections for which one can distinguish between neutrino and DM signals, for a variety of materials. These results will have important implications for experiments that can probe sub-GeV DM-electron scattering such as SENSEI and SuperCDMS.
We discuss the early stages of the MINER coherent neutrino scattering reactor experiment at Texas A&M University. We examine the solar neutrino background both as motivation for the development of new ultra-low threshold detectors to observe coherent scattering and for establishing a baseline event rate to assist in ongoing searches for dark matter. The latter allows for predictive statistical analysis in which potential deviations from this baseline due to non-standard interactions would help shed light on beyond standard model properties of neutrinos and could provide a more clearly defined direction for dark matter searches.
In this talk, I will discuss a novel program of fixed-target searches for thermal-origin Dark Matter (DM), which couples inelastically to the Standard Model. Since the DM only interacts by transitioning to a heavier state, freeze-out proceeds via coannihilation and the unstable heavier state is depleted at later times. For sufficiently large mass splittings, direct detection is kinematically forbidden and indirect detection is impossible, so this scenario can only be tested with accelerators. I will focus on proposed new searches at proton and electron beam fixed-target experiments to probe sub-GeV coannihilation. These searches exploit the distinctive signals of up- and down-scattering as well as decay of the excited state inside the detector volume. I will focus on a representative model in which DM is a pseudo-Dirac fermion coupled to a hidden gauge field (dark photon), which kinetically mixes with the visible photon. Within this framework, I will present the existing bounds obtained by reanalyzing results from previous experiments. I will show that LSND, E137, and BaBar data already place strong constraints on the parameter space consistent with a thermal freeze-out origin, and that future searches at Belle II and MiniBooNE, as well as recently-proposed fixed-target experiments such as LDMX and BDX, can cover nearly all remaining gaps.
We investigate the detection prospects of a non-standard dark sector in the context of boosted dark matter. We consider a scenario where two stable particles have a large mass difference and the heavier particle accounts for most of dark matter in our current universe. The heavier candidate is assumed to have no interaction with the standard model particles at tree-level, hence evading existing constraints. Although subdominant, the lighter dark matter particles are efficiently produced via pair-annihilation of the heavier ones in the center of the Galaxy or the Sun. The large Lorentz boost enables detection of the non-minimal dark sector in large volume terrestrial experiments via exchange of a light dark photon with electrons or nuclei. Various experiments designed for neutrino physics and proton decay are examined in detail, including Super-K and Hyper-K. In this study, we focus on the sensitivity of the far detector at the Deep Underground Neutrino Experiment for boosted dark matter produced in the center of the Sun.
The expansion rate of the universe had a strong influence on the origin of the dark matter abundance during the early stages of the universe's evolution, mainly prior to big-bang nucleosynthesis. Any departure of the expansion rate of the universe from the standard cosmological model during that time can modify the dark matter abundance. In this talk, I will explore the role played by a scalar field on the modification of the expansion rate of the universe arising from scalar-tensor theories of gravity coupled both conformally and disformally to matter, and also, I will show how these variations to the expansion rate would modify the dark matter content of the Universe.
We discuss a new alternative to the Weakly Interacting Massive Particle (WIMP) paradigm for dark matter. Rather than being determined by thermal freeze-out, the dark matter abundance in this scenario is set by dark matter decay, which is allowed for a limited amount of time just before the electroweak phase transition. More specifically, we consider fermionic singlet dark matter particles coupled weakly to a scalar mediator $S_3$ and to auxiliary dark sector fields, charged under the Standard Model gauge groups. Dark matter freezes out while still relativistic, so its abundance is initially very large. As the Universe cools down, the scalar mediator develops a vacuum expectation value (vev), which breaks the symmetry that stabilises dark matter. This allows dark matter to mix with charged fermions and decay. During this epoch, the dark matter abundance is reduced to give the value observed today. Later, the SM Higgs field also develops a vev, which feeds back into the $S_3$ potential and restores the dark sector symmetry. In this concrete model we show that this ``vev flip-flop'' scenario is phenomenologically successful in the most interesting regions of its parameter space and we comment on detection prospects.
Supersymmetric models with radiatively-driven naturalness enjoy modest electroweak fine-tuning at the 10% level while respecting LHC sparticle and Higgs mass constraints. These models have an inverted electroweakino spectrum with $\mu < M_{1} < M_{2} < M_{3}$ leading to a rather clean same-sign diboson signature from wino pair production at hadron colliders. We examine aspects of signal and background for the SSdB signature at high luminosity LHC (HL-LHC). We evaluate the HL-LHC reach in the SSdB channel for $3000$ $fb^{-1}$. The rather clean production/decay topology admits a wino mass measurement from direct counting rate. The mass measurement may also be verified using distributions in variables such as $m_{T_{2}}$.
Combining anomaly with $Z^{\prime}$ mediation of SUSY breaking allows us to solve the tachyonic problem of the former and avoid fine tuning in the latter. This scenario includes an extra $U(1)^{\prime}$ gauge symmetry and extra singlet scalar $S$ which provides a solution to the `$\mu$ problem' of the MSSM. The low-energy particle spectrum is calculated from the UV inputs using the Renormalization Group Equations. The benchmark points considered in the original model, suggested before the Higgs discovery, predicted a Higgs mass close to the current measured value of 125 $~\mathrm{GeV}$. We use the current LHC data to update the predictions of the model, its particle spectrum and in particular the mass of the $Z^{\prime}$ gauge boson.
We study the phenomenology of a supersymmetric extension of the Standard Model with an $R$-symmetry under which $R$-charges correspond to the baryon number. This identification allows for the presence in the superpotential of the $R$-parity violating term $\lambda''U^c D^c D^c$ without breaking baryon number, which loosens several bounds on this operator while changing considerably the phenomenology. However, the $R$-symmetry cannot remain exact as it is at least broken by anomaly mediation. Under these conditions, we investigate the constraints coming from recent ATLAS and CMS experimental searches and use these to place limits on the parameter space of the model. This is done for both stop production, which now features both pair and resonant production, and pair production of the first two generations of squarks.
Flavor symmetries à la Froggatt-Nielsen (FN) provide a compelling way to explain the hierarchies of fermionic masses and mixing angles in the Yukawa sector. In Supersymmetric~(SUSY) extensions of the Standard Model where the mediation of SUSY breaking occurs at scales larger than the breaking of flavor, this symmetry must be respected not only by the Yukawas of the superpotential, but by the soft-breaking masses and trilinear terms as well. In this work we show that contrary to naive expectations, even starting with completely flavor blind soft-breaking in the full theory at high scales, the low-energy sfermion mass matrices and trilinear terms of the effective theory, obtained upon integrating out the heavy mediator fields, are strongly non-universal. We explore the phenomenology of these SUSY flavor models after the latest LHC searches for new physics.
Matching a full theory onto an effective field theory by integrating out heavy fields is often useful for connecting low-energy phenomenology to high-scale physics. I introduce a new formulation of one-loop matching in terms of covariant diagrams, which, unlike conventional Feynman diagrams, preserve gauge covariance in intermediate steps and thus simplify calculations. I will show examples of the use of covariant diagrams in computing SUSY threshold corrections, which helps build connection between unification and phenomenology.
We present a dynamical cosmological solution that simultaneously
accounts for the early inflationary stage of the Universe and solves the
supersymmetric little hierarchy problem via the relaxion mechanism. First,
we consider an inflationary potential arising from the $D$-term of a new $U(1)$ gauge symmetry with a Fayet--Iliopolous term, that is independent of the relaxion. A technically natural, small $U(1)$ gauge coupling, $g< 10^{-8}$, allows for a low Hubble scale of inflation, $H_I< 10^5$ GeV, which is shown to be consistent with Planck data. This feature is then used to realize a supersymmetric two-field relaxion mechanism, where the second field is identified as the inflaton provided that $H_I< 10$ GeV. The inflaton controls the relaxion barrier height allowing the relaxion to evolve in the early Universe and scan the supersymmetric soft masses. After electroweak symmetry is broken, the relaxion settles at a local supersymmetry-breaking minimum with a range of $F$-term values that can naturally explain supersymmetric soft mass
scales up to $10^6$ GeV.
Supersymetric models are subject both to direct constraints from collider searches and to indirect limits from electroweak observables such as the Higgs mass and flavor-changing processes. A minimal scenario consistent with current experimental data suggests a supersymmetric spectrum with a split sfermion sector. Such a spectrum can naturally be realized when supersymmetry is broken in a warped geometry where the sfermion spectrum is related to the Standard Model fermion mass hierarchy. We present a supersymmetric model constructed in AdS$_5$ compactified over an orbifold that predicts a sfermion mass spectrum with an inverted Yukawa coupling hierarchy. Gauginos and Higgsinos are typically several TeV, while the third-generation sfermions are around 10 TeV, consistent with the observed 125 GeV Higgs mass. The first- and second-generation sfermions are above 100 TeV, ameliorating the flavor problem. The gravitino, in the keV to GeV mass range, is the LSP, providing a warm dark matter candidate. We explore the rich parameter space of the model and discuss the details of the sparticle spectrum and its calculation.
The prospect of heavy super-partners in the MSSM is often met with criticism on the grounds of naturalness arguments. We present a recently proposed methodology for studying the little hierarchy problem that can lead to contrasting conclusions. This approach focuses on hierarchies between the EW and SUSY scales that can be achieved without specifying model parameters beyond one significant digit in a way that automatically eliminates scenarios with accidentally large outcomes. Applying this methodology to constrained versions of the minimal supersymmetric standard model, we show the maximal hierarchies that can be achieved range from one to three orders of magnitude depending on the complexity of the model.