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The 2019 Phenomenology Symposium will be held May 6-8, 2019 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 15, 2019
Registration closed April 29, 2019
Talk submission ended April 22, 2019
Conference banquet May 7, 2019
WARNING: HOTEL SCAM
There is a scam going on regarding our hotel bookings. All hotel bookings should be done by the participants individually. No one should contact you with regards to a hotel reservation that you did not make yourself! If you have any further questions, please contact us at pittpacc@pitt.edu.
Confirmed plenary speakers and topics:
Mini-Reviews:
Forum on early career development. Moderator: Sekhar Chivukula (UCSD)
May 6, 1:00-2:00 PM
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 19. 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 19 travel assistance". The decision will be based on the academic qualification, the talk submission to Pheno 19, 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 2019 ORGANIZERS: Brian Batell, Joshua Berger, Cindy Cercone, Ayres Freitas, Joni George, Dorival Gonçalves, Tao Han (chair), Ahmed Ismail, Adam Leibovich, Natália Maia, and Cédric Weiland.
PHENO 2019 PROGRAM ADVISORS: Vernon Barger, Lisa Everett, Kaoru Hagiwara, JoAnne Hewett, Tae Min Hong, Arthur Kosowsky, Yao-Yuan Mao, James Mueller, Vittorio Paolone, Tilman Plehn, Vladimir Savinov, Xerxes Tata, Andrew Zentner, and Dieter Zeppenfeld.
LOCAL EVENTS
The Pittsburgh Marathon will take place May 5, 2019.
The Pittsburgh Pirates baseball team will play the Oakland A's and Texas Rangers.
Sunday May 5 at 1:35 PM vs. Oakland A's
Wednesday May 8 at 12:35 PM vs. Texas Rangers
More information to come.
We consider a generic framework for axion-like particles (ALPs) by introducing a complex scalar singlet field. The breaking of the corresponding global U(1) symmetry at some high scale leads to a (pseudo) Goldstone boson that is identified as the ALP. We show that if the complex scalar field is coupled to the Standard Model Higgs boson, there exists a large parameter space for which the U(1) breaking is strongly first order, thereby producing stochastic gravitational waves that are potentially observable in current and future gravitational-wave detectors.
Axion-like particles (ALPs) produced in the core of a neutron star can convert to photons in the magnetosphere, leading to possible signatures in the soft and hard X-ray emission from these sources. We study these signatures taking the magnetar SGR 1806-20 as an example. In particular, assuming ALP emission rates from the core that are just subdominant to neutrino emission, the parameter space of ALPs can be constrained by the requirement that the luminosity from ALP-to-photon conversion should not exceed the total observed luminosity from the magnetar. Up to astrophysical uncertainties pertaining to the core temperature, these constraints are competitive with constraints from helioscope experiments in the relevant part of ALP parameter space. Another class of signatures in this context are polarized X-rays, since ALPs only mix with the parallel component of the photon. These polarization signals may be observable by IXPE (in the 2-8 keV range) and X-Calibur (in the 15-60 keV range).
White dwarf (WD) stars may radiate keV-energy axions produced in their stellar cores. This has been extensively studied as an extra channel by which WDs may cool, with some analyses even suggesting that axions can help explain the observed WD luminosity function. We show that the radiated axions may convert into X-rays in the strong magnetic fields surrounding the WDs, leading to observable X-ray signatures. We use Suzaku observations of the WD RE J0317-853 to set the strongest constraints to-date on the combination of the axion-electron times axion-photon couplings, and we show that dedicated observations of magnetic WDs by telescopes such as Chandra, XMM-Newton, and NuSTAR could increase the sensitivity to these couplings by over an order of magnitude, allowing for a definitive test of the axion-like-particle explanation of the stellar cooling anomalies.
Axions, which can solve the Strong CP problem, and axion-like particles (ALPs), which arise naturally in many models of high-scale physics, provide theoretically compelling dark matter candidates. Axions and ALPs which couple to photons have been shown to produce observable radio emission through their conversion to photons in the magnetospheres of neutron stars, providing a means of indirect detection. In this work, we analyze 1 hour of radio data collected by the Effelsberg 100-m Radio Telescope to place novel constraints on 𝜇eV axion dark matter. We also briefly discuss implications of dark matter substructure for this search strategy.
Ultracompact dark matter (DM) minihalos at characteristic masses at and below $10^{-10}$ solar masses are expected to arise in axion DM models where the Peccei-Quinn (PQ) symmetry is broken after inflation. The minihalos arise from density perturbations that are generated through the collapse of the axion-string and domain-wall network during the quantum chromodynamics (QCD) phase-transition, combined with the non-trivial axion self-interactions. We perform some of the highest-resolution simulations of this scenario to date starting at the epoch before the PQ phase transition and ending after the QCD phase transition, once the axion has entered the linear regime. We characterize the spectrum of minihalos that are generated and comment on implications for efforts to detect axion DM. We also compute the total DM density at different axion masses and present a value for the axion mass for which the correct DM density is obtained.
The QCD axion is a viable dark matter candidate as the misalignment mechanism can furnish the observed dark matter abundance. Although a wide range of axion decay constants $f_a$ are compatible with astrophysical bounds, very large $f_a \sim\mathcal{O}(10^{17}-10^{18}$) GeV (and small $f_a\sim \mathcal{O}(10^9-10^{10})$ GeV) values require a misalignment angle $\theta_\text{mis} \ll 1$ $(\pi - \theta_\text{mis} \ll 1$) which presents a fine-tuning problem. These decay constant values are within projected experimental sensitivity of planned and proposed experiments, which further motivates their investigation. I will present a new mechanism, called Dynamical Axion Misalignment Production (DAMP), wherein these misalignment angles arise naturally. In addition to the presenting criteria for a DAMP model I will discuss, as a proof of principle, a set of SUSY QCD models which exhibit DAMP. These models predict a precise value for $f_a$ and the absence of isocurvature perturbations.
We consider a partially composite axion which results from a linear mixing between an elementary scalar and a composite operator of dimension four. Non-perturbative effects generate a mass for the partially composite axion and mix it with the heavier axion states. This causes the misalignment mechanism to produce multiple axions with different abundances and leads to new interesting phenomenology in dynamical dark matter models.
The IceCube Neutrino Observatory detects high energy astrophysical neutrinos in two event topologies: tracks and cascades. Since the flavor composition of each event topology differs, tracks and cascades can be used to test the neutrino properties and the mechanisms behind the neutrino production in astrophysical sources. Assuming a conventional model for the neutrino production, the IceCube data sets related to the two channels are in >3σ tension with each other. Invisible neutrino decay with lifetime τ/m=100 s/eV solves this tension. Noticeably, it leads to an improvement over the standard non-decay scenario of more than 3σ while remaining consistent with all other multi-messenger observations. In addition, our invisible neutrino decay model predicts a reduction of 59% in the number of observed ντ events which is consistent with the current observational deficit.
Due to IceCube, neutrino astrophysics is entering a new era, which will allow powerful new probes of both astrophysics and particle physics. We investigate new signatures from high-energy neutrinos in IceCube that can help discriminate among presently allowed scenarios.
We propose a simultaneous explanation of two recent anomalous observations at very different energy scales. The first one concerns hints of lepton flavor universality violation in rare B-meson decays, as observed by LHCb, and to some extent, by Belle and BaBar. The second anomaly is the observation made by the ANITA balloon experiment of two EeV upgoing air showers. Both these observations are challenging to explain within the Standard Model. We show that there exists a natural explanation for both the anomalies in the framework of R-parity violating supersymmetric extension of the Standard Model with TeV-scale squarks and a GeV-scale bino, which are consistent with all existing constraints from the LHC and low-energy experiments. This scenario could be fully tested in the near future and provides a complementary way to discover supersymmetry.
The ANITA collaboration recently reported the detection of two anomalous upward-propagating extensive air showers exiting the Earth with relatively large emergence angles and energies in the range O(0.5−1) EeV. We interpret these two events as coming from the decay of a massive dark-matter candidate (mDM≳109 GeV) decaying into a pair of right-handed neutrinos. While propagating through the Earth, these extremely boosted decay products convert eventually to τ-leptons which loose energy during their propagation and produce showers in the atmosphere detectable by ANITA at emergence angles larger than what Standard-Model neutrinos could ever produce. We performed Monte Carlo simulations to estimate the propagation and energy loss effects and derived differential effective areas and number of events for the ANITA and the IceCube detectors. Interestingly, the expected number of events for IceCube is of the very same order of magnitude than the number of events observed by ANITA but at larger emergence angles, and energies ≲0.1 EeV. Such features match perfectly with the presence of the two upward-going events IceCube-140109 and IceCube-121205 that have been exhibited from a recent re-analysis of IceCube data samples.
We have shown a new way of obtaining Leptogenesis at low-scale (i.e around TeV scale) through annihilating t-channel process. In order to show the working of the mechanism in a minimal model, we have shown the same in "Scotogenic" model where the Standard model is extended by a Z2 odd scalar doublet and three right-handed neutrinos.
The possibility of generating the baryon asymmetry of the Universe via
flavor oscillation in the early Universe is discussed. After the inflation, leptons are born in some states, travel in the medium, and are eventually projected onto flavor eigenstates due to the scattering via the Yukawa interactions. By using the Lagrangian of the Standard Model with the Majorana neutrino mass terms, $llHH$, we follow the time evolution of the density matrices of the leptons in this very first stage of the Universe and show that the CP violation in the flavor oscillation can explain the baryon asymmetry of the Universe. In the scenario where the reheating is caused by the decay of the inflaton into the Higgs bosons, the baryon asymmetry is generated by the CP phases in the Pontecorvo-Maki-Nakagawa-Sakata matrix and thus can be tested by the low energy neutrino experiments.
Although it has been a half century since the discovery of standard model neutrinos, there is still no concrete evidence of the sum of their masses and lifetimes. If neutrinos decay at cosmological time scales, we demonstrate that precision cosmological data from large scale structure (LSS) and CMB lensing measurements can probe both neutrino lifetime and the sum of masses. In this talk, I will point out that (i) allowing neutrinos decay will relax the current bound on neutrino mass from cosmological data and (ii) near future measurements (e.g. Euclid) are sufficient to break the degeneracy between neutrino masses and their lifetimes. We set a 2D limit on the sum of neutrino masses and lifetime using current LSS and CMB data. Such limit is orders of magnitude stronger than all other current limits on non-radiative neutrino decay width.
Extraction of the strange quark PDF is a long standing puzzle. We use
nCTEQ nPDFs with uncertainties to examine W/Z production at the LHC
and try to study both the nuclear corrections and the flavor
differentiation. This complements the information from neutrino-DIS
data. Additionally, we look ahead to future facilities such as EIC,
LHeC, and LHC upgrades and use a new tool, PDFSense, to estimate the
impact.
It is crucial to reduce PDF (Parton Distribution Function) uncertainties in the LHC precision era, so one would be very curious to know what kinds of observables can reduce PDF uncertainties and to what extent. Following this idea, we present a software package ePump, based on Hessian approximation, which can quickly update a set of global-fit PDFs including error PDFs. ePump can reproduce the CT14HERA2 PDFs very well and can help identify the impact of each data set used in the CTEQ global-fit. Only about one third of the data sets dominate the fit. Finally, we use ePump to analyze how some new LHC data constrain PDFs.
We consider the process of W-boson hadroproduction in association with jets, including leptonic decays of the W boson. We compute the full set of next-to-leading (NLO) corrections at order $\mathcal{O}(\alpha^2\alpha_s^2)$ and $\mathcal{O}(\alpha^3\alpha_s)$ and given by QCD and electroweak corrections to W plus one jet production and QCD corrections to W production in association with a photon. We also take into account photon-induced processes and mixed interference contributions at order $\mathcal{O}(\alpha^3\alpha_s)$. We match the NLO corrections to a Parton Shower (PS) according to the POWHEG+MiNLO approach and make all the contributions available in the POWHEG-BOX-RES version of the POWHEG generator. The calculation can also be used to obtain predictions for the process of W -boson production associated to a photon at NLO+PS QCD accuracy. We show illustrative phenomenological results of interest for physics studies at the LHC.
We study the multiple soft gluon radiation effects in Z boson plus jet production at the LHC. By applying the transverse momentum dependent factorization formalism, the large logarithms introduced by the small total transverse momentum of the Z boson plus jet final state system, are resummed to all orders in the expansion of the strong interaction coupling at the accuracy of Next- to-Leading Logarithm(NLL). We also compare our results with the CMS data by the reweighting method to include the effects from Z boson decay and the kinematical cuts on the leptons . It shows our resummation calculation agree with data very well for both the total transverse momentum and the azimuthal angle correlations of the final state Z boson and jet system
We compute the Mixed $QCD\times EW$ double virtual corrections $(O(\alpha \alpha_s))$ to Drell Yan production of W and Z bosons. We present the explicit analytic results of unrenormalized form factors which are numerically evaluated for different phase space points. For our calculation we used IBP reductions to write the form factors in terms of a handful of master integrals. These master integrals are collected from results available in literature and they are numerically checked using SecDec.
We present the calculation of the process $H\to b\overline{b}j$ at next-to-next-to-leading order (NNLO) accuracy. We consider contributions in which the Higgs boson couples directly to bottom quarks, i.e. our predictions are accurate to order $\mathcal{O}(\alpha_s^3 y_b^2)$. We compute the various components needed to construct the NNLO contribution, including an independent calculation of the two-loop amplitudes. We compare our results for the two-loop amplitudes to an existing calculation (finding partial agreement) and we present multiple checks on our two-loop expression using the known infrared factorization properties as the emitted gluon becomes soft or collinear. We use our results to construct a Monte Carlo implementation of $H\to b\overline{b}j$ and present jet rates and differential distributions in the Higgs rest frame using the Durham jet algorithm.
We present a fully-differential calculation of the H → bb decay at next-to-next- to-next-to-leading order (N3LO) accuracy. Our calculation considers diagrams in which the Higgs boson couples directly to the bottom quarks. In order to regulate the infrared divergences present at this order we use the Projection-to-Born technique coupled with N-jettiness slicing. After validating our methodology at next-to-next-to-leading order (NNLO) we present exclusive jet rates and differential distributions for jet observables at N3LO accuracy using the Durham jet algorithm in the Higgs rest frame.
It is extremely challenging to probe the charm-quark Yukawa coupling at hadron colliders primarily due to the large Standard Model (SM) background (including $h\to b\bar b$) and the lack of an effective trigger for the signal $h\to c\bar c$. We examine the feasibility of probing this coupling at the LHC via a Higgs radiative decay $h\rightarrow c\bar{c}\gamma$. The existence of an additional photon in the final state may help for the signal identification and background suppression. Adopting a refined triggering strategy and utilizing basic machine learning, we find that a coupling limit of about 8 times the SM value may be reached with $2\sigma$ sensitivity after the High Luminosity LHC (HL-LHC). Our result is comparable and complementary to other projections for direct and indirect probes of $h\to c\bar c$ at the HL-LHC. Without a significant change in detector capabilities, there would be no significant improvement for this search from higher energy hadron colliders.
The conjoined production at the LHC of single top and Higgs boson via t-channel weak boson exchange is ideal to probe the top-quark Yukawa coupling, due to a delicate cancellation between the amplitudes with the htt and the hWW couplings. We find that the top quark is produced with 100% polarization in the leading order, and its quantum state is determined by the spin-vector direction in the t-quark rest frame. We relate the spin direction to the four-momenta of the top, Higgs and a jet in the helicity amplitude framework. We identify a polarization asymmetry that is sensitive to CP violation, even after partial integration over the forward jet momentum. This CP violating asymmetry may be observed at the LHC via the component of the top-quark polarization that is perpendicular to the th scattering plane.
In this ongoing work, we study the phenomenology of Higgs pair production with a pair of top quarks ($pp\to t\bar{t}hh$) at the HL-LHC. Several final state/channels are simulated and evaluated with the help of multivariable analysis techniques. It turns out that the multi-$b$ + single lepton channel contributes the most to the signal significance, followed by the same-sign dilepton channel. The constraints on $hhh$ and $t\bar{t}hh$ couplingss are comparable to those gained from Di-Higgs or VBF analyses. We also discuss the potential of $t\bar{t}hh$ as a probe of resonances in new physics such as top partner pair production or heavy Higgs bosons.
I will be discussing constraints on light dark matter and the effects of the astrophysical neutrino
background. This will include a discussion of bremsstrahlung, the Migdal effect, and dark matter
scattered by cosmic rays, as well as the effect of these processes on the background induced by
coherent elastic neutrino-nucleus scattering.
The non-detection of GeV-scale WIMPs has led to increased interest in more general candidates, including sub-GeV dark matter. Direct detection experiments, despite their high sensitivity to WIMPs, are nominally blind to dark matter much lighter than ∼1 GeV. Recent work has shown that cosmic rays scattering with sub-GeV dark matter would both alter the observed cosmic ray spectra and produce a flux of relativistic dark matter, which would be detectable with both traditional dark matter experiments and neutrino detectors. Using data, detectors, and analysis techniques not previously considered, we substantially increase the regions of parameter space excluded by neutrino experiments for both dark matter-nucleon and dark matter-electron scattering.
Within the Dynamical Dark Matter (DDM) framework, an ensemble of unstable particle species whose decay widths are balanced against their cosmological abundances collectively constitutes the dark matter in our universe. The constraints on DDM ensembles whose constituent particles decay to visible-sector particles with a non-negligible branching fraction are well established and quite stringent. However, the constraints on ensembles whose constituent particles decay exclusively to other, lighter dark-sector states are less well established. In this talk, I examine the extent to which information about the expansion rate of the universe at low redshifts gleaned from observations of Type-Ia supernovae can serve to constrain the parameter space of invisibly-decaying DDM ensembles.
The Milky Way halo is the brightest source of dark matter annihilation on the sky. Indeed, the potential strength of the Galactic dark matter signal can supersede that expected from dwarf galaxies and galaxy groups even in regions away from the Inner Galaxy. We present the results of a search for dark matter annihilation in the smooth Milky Way halo for $|b| > 20^\circ$ and $r < 50^\circ$ using 413 weeks of Fermi Pass 8 data within the energy range of $\sim$0.8–50 GeV. We exclude thermal dark matter with mass below $\sim$70 GeV that annihilates to $b\bar{b}$ at the 95% confidence level using the p6v11 cosmic-ray foreground model, providing the strongest limits on the annihilation cross section in this mass range. These results exclude the region of dark matter parameter space that is consistent with the excess of $\sim$GeV photons observed at the Galactic Center for the $b\bar{b}$ annihilation channel and, for the first time, put the $\tau^+\tau^-$ explanation under tension. We explore how these results depend on uncertainties in the foregrounds by varying over a set of reasonable models.
In this talk, I will discuss predictions of anomaly-free dark matter models for direct and indirect detection experiments. In these models, a fermionic dark matter candidate is predicted by anomaly cancellation, its mass is defined by the new symmetry breaking scale, and its stability is guaranteed by a remnant symmetry after the gauge symmetry is broken. Relic density and perturbative constraints provide an upper bound on the symmetry breaking scale of 30 TeV. In addition, the model leads to gamma lines that can be distinguished from the continuum. [arXiv:1904.01017]
Many proposals for physics beyond the Standard Model give rise to a non-minimal dark sector containing many degrees of freedom. In this talk, we explore the cosmological implications of the non-trivial dynamics which may arise within such dark sectors, focusing on decay processes which take place entirely among the dark constituents. First, we demonstrate that such decays can leave dramatic imprints on the resulting dark-matter phase-space distribution. In particular, this phase-space distribution need not be thermal — it can even be multi-modal, exhibiting a pattern of peaks and troughs as a function of momentum. We then proceed to show how these features can induce small-scale modifications to the matter power spectrum. Finally, we assess the extent to which one can approach the archaeological “inverse” problem of deciphering the properties of an underlying dark sector from the matter power spectrum. Our results therefore provide an interesting way to learn about, and potentially constrain, the features of non-minimal dark sectors and their dynamics in the early universe.
I will review the theoretical motivations and experimental signatures for vectorlike fermions.
Vectorlike leptons are an intriguing possibility for physics beyond the Standard Model. We study the reach for discovering or excluding models of vectorlike leptons that mix predominantly with the tau, using multilepton signatures at various future proton-proton collider options: a high-luminosity LHC with Sqrt[s] = 14 TeV, a high-energy collider with Sqrt[s] = 27 TeV, and possible new longer-tunnel colliders with Sqrt[s] = 70 or 100 TeV
Standard Model Effective Theory (SMEFT) is a powerful tool to constrain new physics in a rather model-independent way. A lot of work has been done to constrain the army of dimension-six operators at next-to-leading order but a rather important subset - four-fermi operators - has been neglected so far. We derive and put into perspective the bounds from the W-polarization fractions associated with top quark decay and Z decay partial widths as well as the weak mixing angle. On the technical side we work out the often neglected subtleties when treating chiral interactions in dimensional regularization.
Measurements of the inclusive and differential top-quark pair production cross sections in proton-proton collisions at a centre-of-mass energy of 13 TeV with the ATLAS detector at the Large Hadron Collider are presented. The investigated final states include ttbar+jets events, in particular ttbar+heavy flavour jets. The process of a ttbar pair produced in association with jets originating from b-quarks (b-jets) is particularly important to measure, as there are many uncertainties in the calculation of the process due to the relevance of multiple energy scales. The differential measurements reach high precision and are compared to the best available theoretical calculations. These measurements 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 fixed-order QCD calculations.
Precise measurements of the properties of the top quark test the Standard Model (SM) and can be used to constrain new physics models. The top-quark is predicted in the SM to decay almost exclusively into a W boson and a b-quark. We present a wide range of searches for non-SM top quark decays using the 13 TeV ATLAS datasets, including flavour-changing current processes t$\to$qH and t$\to$qZ. In addition, measurements of the spin correlation, colour flow and top quark mass in ttbar production are also presented.
We present a fully differential and spin-dependent t-channel single-top-quark calculation at next-to-leading order (NLO) in QCD including off-shell effects by using the complex mass scheme in the Standard Model (SM) and in the Standard Model Effective Field Theory (SMEFT). We include all relevant SMEFT operators at 1/Λ^2 that contribute at NLO in QCD for a fully consistent comparison to the SM at NLO. In addition, we include chirality flipping operators that do not interfere with the SM amplitude and contribute only at 1/Λ^4 with a massless b-quark. Such higher order effects are usually captured by considering anomalous right-handed Wtb and left-handed Wtb tensor couplings. Despite their formal suppression in the SMEFT, they describe an important class of models for new physics.
We study the prospect of discovering a rare $t \to c h^0$ decay in the top pair production channel at LHC. We follow a general two Higgs doublet model framework to investigate this signature, with Higgs decaying into $\tau \tau$ and another top decaying hadronically to a b quark and two light jets. We search for the following final states $b j j \ell^+ \ell^- + Missing Energy$ and $b j j \ell^{\pm} \tau_h + Missing Energy $, where $\tau_h$ refers to jets coming from $\tau$ decay. We present our Monte Carlo analysis using Delphes. We use boosted decision trees for discrimination at current and Future HL-LHC and HE-LHC.
Double gauge boson production is one of the most important processes under study at the LHC. Of particular importance is the measurement of the trilinear electroweak gauge boson coupling, which sheds light on the gauge structure of the Standard Model. We study the impact of anomalous gauge boson and fermion couplings on the production of W+W− pairs at the LHC and how these couplings affect the measurements of the trilinear gauge boson couplings. Although constrained to be very small by LEP, anomalous fermion-gauge boson couplings can have important effects in LHC fits to anomalous couplings due to a strong growth with energy. We perform this study at NLO in QCD, determining the effects of higher order corrections as well.
The scattering of electroweak bosons tests the gauge structure of the Standard Model and is
sensitive to anomalous quartic gauge couplings. In this talk, we present recent results on vector-
boson scattering from the ATLAS experiment using proton-proton collisions at √s=13 TeV. This
includes the observation of WZ and same-sign-WW production via vector-boson scattering along
with a measurement of VV production in semileptonic final states. If available, a measurement of
Zγ production via vector-boson scattering will also be presented. The results can be used to
constrain new physics that manifests as anomalous electroweak-boson self interactions.
The production of multiple electroweak bosons at the LHC constitutes a stringent test of the electroweak sector and provide a model-independent means to search for new physics at the TeV scale. In this talk, we present recent results for inclusive WW, WZ, ZZ and Zγ production in proton-proton collisions at √s=13 TeV collected by the ATLAS experiment. The data are sensitive to anomalous triple gauge couplings and are reinterpreted in terms of an effective field theory to constrain new physics beyond the Standard Model. In addition, the unfolded differential cross section for four-lepton production is presented and compared to state-of-the-art Standard Model calculations. Finally a search for the production of three massive vector bosons in WWW, WWZ and WZZ final states is presented.
The XENON1T direct dark matter search experiment is a dual-phase xenon Time Projection Chamber used to search for WIMP interactions in a 2-ton active liquid xenon target. With a recent series of publications, the XENON collaboration has used a tonne-year exposure of XENON1T, with the lowest background rate of any current dark matter search experiment, to constrain leading models of WIMP interactions. This talk will summarize these results, which include the most stringent limits on the spin-independent WIMP-nucleon, scalar WIMP-pion, and spin-dependent WIMP-neutron scattering cross sections.
In fermionic dark matter (DM) models with pseudoscalar mediators, the tree-level amplitude for the DM-nucleon elastic scattering is suppressed by the momentum transfer in the non-relativistic limit. However, it is not suppressed at the loop level, and thus the loop corrections are essential to discuss the sensitivities of the direct detection experiments for the model prediction. In particular, two-loop diagrams give a leading order contribution for an operator with gluon fields but were not correctly evaluated. Moreover, some interaction terms which affect the scattering cross section were overlooked. In this talk, we show the cross section obtained by the improved analysis and discuss the region where the cross section becomes large.
Current dark matter direct detection searches can be split into two broad classes: elastic scattering and absorption, with the latter reserved purely for bosonic dark matter. In this work, we study a new class of signal: absorption of fermionic dark matter. We present the lowest-dimension operators which make this possible, their implications, and their simple UV completions. Most importantly, such dark matter is inherently unstable as there is no symmetry which protects it against decays into standard model fermions. Nevertheless, we show that fermionic dark matter absorption can be searched for in current and future direct detection and neutrino experiments, while ensuring consistency with its observed abundance and required lifetime.
I will present new constraints on dark matter in the eV-to-GeV mass scale range, obtained by a prototype detector of the Sub-Electron-Noise Skipper-CCD Experimental Instrument (SENSEI). We took our first data in 2018 searching for dark matter-electron interactions in silicon and observe how many electrons are excited across the silicon band gap per event. We found no events with three or more electrons; however, we had some background of one- and two-electron events. We used this data to put the strongest bounds of any experiment so far on dark matter-electron scattering for masses between 500 keV to 5 MeV, and on dark-photon dark matter being absorbed by electrons for a range of masses below 12.4 eV. We expect SENSEI to push these bounds further in the near future with upcoming runs of larger exposures and with higher grade detectors and more significant background reduction.
Scatterings both on electrons and nuclei of the Earth crust, atmosphere, and shielding attenuate the expected local dark matter flux at a terrestrial detector. Such experiments lose sensitivity to dark matter above some critical cross section, and do not probe potentially stronger interactions. In this talk, I consider a simple model of the dark sector with a dark photon in the two limits of heavy and ultralight mediators. In this model, the dark matter-electron scattering cross-section is directly linked to the dark matter-nucleus cross section, and nuclear interactions typically dominate the attenuation process. I will present the exclusion bands for various experiments computed using Monte Carlo simulations, and also the constraint’s behaviour for various scenarios. Apart from the dark photon model, I also consider the case where the dark matter couples exclusively to electrons, and show the corresponding constraints computed via analytic methods. Finally, I will discuss the prospects and modulation signature of small scale, balloon and satellite borne direct detection experiments.
Recently, we proposed paleo-detectors as a method for the direct detection of Weakly Interacting Massive Particle (WIMP) dark matter. In paleo-detectors, one would search for the persistent traces left by dark matter-nucleon interactions in ancient minerals. For sufficiently radiopure target materials obtained from boreholes deep enough to avoid cosmogenic backgrounds, we identify (broadly speaking) two different background regimes. For low-mass WIMPs with masses $m_\chi < 10\,$GeV, the largest contribution to the background budget comes from nuclear recoils induced by coherent scattering of solar neutrinos. For heavier WIMPs, the largest background source is nuclear recoils induced by fast neutrons arising from trace amounts of radioactivity. In this talk, we discuss the background budget for paleo-detectors and how backgrounds inform which minerals are suitable as targets materials.
Recently, we proposed paleo-detectors as a method for the direct
detection of Weakly Interacting Massive Particle (WIMP) dark matter.
Instead of searching for DM induced nuclear recoils in a real-time
laboratory experiment, we propose to search for the traces of DM
interactions recorded in ancient minerals over geological time-scales.
The large integration times of paleo-detectors would allow to obtain
exposures much larger than what is feasible in conventional direct
detection experiments even for comparatively small target masses. In
this talk, we discuss options for the reconstruction of the WIMP (and
background) induced damage features in paleo-detectors. Then we present
projections for the sensitivity of paleo-detectors to WIMP--nucleon
interactions. Further, we show the potential of paleo-detectors to
reconstruct the WIMP parameters in the hypothetical case of a discovery.
If dark matter is composed of primordial black holes, such black holes can span an enormous range of masses. A variety of observational constraints exist on massive black holes, while black holes with masses below $10^{15}\,\mathrm{g}$ are often assumed to have completely evaporated by the present day. If the evaporation process halts at the Planck scale it would leave behind a stable relic, and such objects could constitute the entirety of dark matter. Neutral Planck-scale relics are effectively invisible to both astrophysical and direct detection searches. However, we argue that such relics may typically carry electric charge, making them visible to terrestrial detectors. We evaluate constraints and detection prospects in detail, and show that if not already ruled out by monopole searches, this scenario can be largely explored within the next decade using existing or planned experimental equipment. A single detection would have enormous implications for cosmology, black hole physics, and quantum gravity.
Light beyond-Standard-Model particles X in the MeV-100 MeV mass range can be produced in the nuclear and hadronic reactions, but would have to decay electromagnetically. We show that the simple and well-understood low-energy hadronic processes can be used as a tool to study X production and decay. In particular, the pion capture process can be used in a new experimental set-up to search for anomalies in the angular distribution of the lepton pair, which could signal the appearance of dark photons, axion-like particles and other exotic states. This process can be used to decisively test the hypothesis of a new particle produced in the 7Li+p reaction.
We investigate the potential of Liquid Argon (LAr) neutrino detectors to search for millicharged
particles, a well-motivated extension of the standard model. Detectors located downstream of an
intense proton beam that is striking a target may be exposed to a large flux of millicharged particles.
Millicharged particles interact primarily through low momentum exchange producing electron recoil
events near detector threshold. Recently, sub-MeV detection capabilities were demonstrated by the
Fermilab ArgoNeuT detector, a small LAr detector which was exposed to the NuMI neutrino beam.
Despite high background rates and its small size, we show that ArgoNeuT is capable of probing
unexplored parameter space with its existing dataset. In particular, we show that the excellent
spatial resolution in LAr detectors allows rejecting backgrounds by requiring two soft hits that are
aligned with the upstream target. We further discuss the prospects of these types of searches in
future larger LAr neutrino detectors such as the DUNE near detector.
Muon electron scattering experiments, like MUonE, offer an opportunity
for an improved measurement of the LO hadronic running of $\alpha$, resulting in a reduced theoretical uncertainty of the leading hadronic effects on the anomalous magnetic moment of the muon. In this talk I present the possible impact of BSM physics on this measurement. In particular I will answer the question if a BSM explanation of the moun $g-2$ could be indirectly fitted into the leading hadronic effects, causing inadvertent agreement with the SM.
The anomalous magnetic moments of the electron and the muon are interesting observables, since they can be measured with great precision and their values can be computed with excellent accuracy within the Standard Model (SM). The current experimental measurement of this quantities show a deviation of a few standard deviations with respect to the SM prediction, which may be a hint of new physics. The fact that the electron and the muon masses differ by two orders of magnitude and the deviations have opposite signs makes it difficult to find a common origin of these anomalies. In this work we introduce a complex singlet scalar charged under a Peccei–Quinn-like (PQ) global symmetry together with the electron transforming chirally under the same symmetry. In this realization, the CP-odd scalar couples to electron only, while the CP-even part can couple to muons and electrons simultaneously. In addition, the CP-odd scalar can naturally be much lighter than the CP-even scalar, as a pseudo-Goldstone boson of the PQ-like symmetry, leading to an explanation of the suppression of the electron anomalous magnetic moment with respect to the SM prediction due to the CP-odd Higgs effect dominance, as well as an enhancement of the muon one induced by the CP-even component.
We consider a simple non-supersymmetric $SO(10)$ grand unification in which a successful unification of the gauge couplings is realized with a two-step symmetry breaking (SB), for example, the $SO(10)$ group is broken into an intermediate Pati-Salam group at $M_{\rm GUT} \simeq 10^{16}$ GeV, which is further broken into the Standard Model (SM) group at an intermediate scale $M_I \simeq 10^{11}$ GeV. Both the SBs produce topologically stable monopoles whose abundance is severely constrained. A low scale inflationary scenario can inflate away these monopoles if the Hubble during the inflation ($H_{inf}$) is smaller than the SB scale which produces them. However, in a simple single field inflation scenario $H_{\rm inf} \gg M_{I}$, and hence the monopoles produced during the PS SB cannot be sufficiently diluted. To solve this problem, we consider an inflection-point inflation (IPI), a unique low scale single field inflation scenario which guarantees $H_{\rm inf}\ll 10^{11}$ GeV. To implement the IPI in the $SO(10)$ model, we propose a simple extension based on a gauge group $SO(10) \times U(1)_\psi$, where an $SO(10)$ singlet scalar is identified to be the inflaton. The model inclues 3 generations of fermions in ${\bf 16}$ ($+1$), ${\bf 10}$ ($-2$), and ${\bf 1}$ ($+4$) representations, where the ${\bf 16}$-plets are the SM fermions (plus RHNs), and the extra new fermions are necessary to make the model anomaly-free. We consider various phenomenological constraints and theoretical consistencies, such as the successful gauge coupling unification, proton decay constraints, and stability of the SM Higgs potential. We identify a model parameter space which satisfies all these constraints. After the SBs a ${\bf Z}_2$ symmetry remains unbroken such that the lightest mass eigenstate of the ${\bf 10}$-plet and the singlet new fermion is a dark matter (DM) candidate. The DM particle communicates with SM particles through SM Higgs portal interactions. We show that the allowed parameter region for the DM scenario will be fully explored by the LUX-ZEPLIN DM experiment in the near future.
Vector-like top partners are a common feature of composite Higgs and Little Higgs models, where they help with the hierarchy problem. Traditional top partners decay primarily into electroweak channels: $t h$, $t Z$, and $b W$. The LHC places lower limits for top partner masses of around 1.1-1.4 TeV from pair production searches, under the assumption of these traditional decay modes. In our model, we introduce a top partner with a dark U(1) charge which, for dark photon masses much smaller than the Z mass, leads generically to a "maverick" top partner with substantial branching ratios to the dark sector channels $t \gamma_d$ and $t h_2$. By largely avoiding the electroweak decay modes, existing top partner searches are much less constraining, and sub-TeV top partners are reopened.
We present a model using up-type vector like quark (VLQ) charged under an additional $U(1)_d$ gauge force, whose gauge boson is the dark photon $\gamma_d$. If the dark photon is much less massive than the standard model electroweak sector ($M_{\gamma_d} \ll M_Z$), the VLQs, which are pair produced via the strong force, predominately decay to dark photons and a dark Higgs that breaks the $U(1)_d$. Hence, the dark photons production rate is predominately determined by the gauge structure and not the small kinetic mixing with hypercharge. In this talk we focus on the allowed leptonic decays of the dark photon presenting branching ratios and decay length calculations. We demonstrate there is a rich phenomenology of dark photon decays with prompt decays, displaced vertices, decays within the detector, and decays outside the detector depending on the parameter choices in the model.
The first direct detections of gravitational waves from the mergers of binary black holes and binary neutron stars by the LIGO and VIRGO experiments have electrified the physics and astronomy communities. A clear next experimental step is an interferometer in space, which can detect lower frequency signals than a ground-based detector, including supermassive black hole binary coalescences from early galaxy mergers and a known stochastic background from confusion-limited white-dwarf binaries. An even more intriguing signal is the stochastic background from early-universe physics. In this talk I will present our recent work (in collaboration with Axel Brandenburg, Arthur Kosowsky, Sayan Mandal, and Alberto Roper Pol). Using direct numerical simulations of early universe hydromagnetic turbulence with energy densities of up to 10% of the radiation energy density, we show that gravitational waves with energy densities of about 10^{-10} times the critical energy density of the Friedmann universe today were produced. Their characteristic strain today is found to be about 10-20 and should be observable with the Laser Interferometer Space Antenna (LISA) in the mHz range. The gravitational waves have positive (negative) circular polarization if the magnetic field has positive (negative) magnetic helicity. The gravitational wave energy reaches a constant value after the turbulent energy (kinetic or magnetic) has reached its maximum. Compressive modes are found to produce about 10 times stronger gravitational waves than solenoidal ones. Finally, I will discuss the range of phase transition energy scales and properties that may be detectable with the envisioned space-based interferometer configurations such as LISA.
Some of the solutions to the hierarchy problem use dimensional transmutation to explain the Planck-weak hierarchy. In these models, the hierarchy is explained by exponentiation of (the inverse of) a small anomalous dimension of the coupling that characterizes the deviation of the theory from scale invariance. The confinement-deconfinement phase transition in these models can be studied using holography, where the confined phase is dual to the compact Randall-Sundrum (RS I) model and the deconfined phase corresponds to an AdS-Schwarzchild geometry. In the minimal model, the transition rate from the confined to the deconfined phase has been previously shown to be suppressed by the same parameter that is controlling the hierarchy, leading either to a large supercooling or an empty universe. In this work we consider the possibility that the deformation grows in the IR and runs towards an IR fixed point. In this scenario, the rate of the phase transition can be controlled by the parameters of the IR fixed point, while the hierarchy is still set by the anomalous dimension corresponding to the UV fixed point. This makes it is possible for the phase transition to complete without undergoing a large supercooling. We then discuss the gravitational wave signal from this phase transition and how it can be distinguished from the minimal model. Remarkably, the gravitational waves may probe the characteristics of the IR fixed point even if it lies well below the confinement scale, i.e. even when confinement would hide the IR fixed point from collider experiments.
The recent discovery of gravitational waves from five binary black hole (BBH) mergers has given us a new way to study our universe. The origin of the black hole (BH) binaries remains unclear. In this talk, I discuss how the BH spin distribution may help us distinguish between primordial or stellar origins. Primordial black holes (PBHs) may have formed due to the collapse of large density fluctuations in the early universe and are generically expected to have nearly vanishing spin, having arisen from the collapse of a distribution of matter without a significant vorticity. So far, all the merger events observed by LIGO-Virgo favor small spin effective values.
Warm inflation is an interesting alternative implementation of a period of accelerated expansion and reheating in the early universe. It turns out to be easy to have a concurrent quasi-thermal radiation bath if energy is extracted from the rolling scalar field via friction. The benefits of warm inflation include automatic reheating at the end of inflation when the thermal bath begins to dominate over the vacuum energy, and a new form of friction that does not require super-Planckian field excursions and suppresses contributions to the scalar-to-tensor ratio $r$. We show that with an axion-like coupling to a non-Abelian group, a thermal bath can be generated with all of these benefits and describe what we call the 'minimal model'.
There has been considerable recent interest in a new class of non-slow roll inflationary solutions known as constant roll inflation. Constant roll solutions are a generalization of the ultra-slow roll (USR) solution, where the first Hubble slow roll parameter $\epsilon$ is small, but the second Hubble slow roll parameter $\eta$ is not. While it is known that the USR solutions represent dynamical transients, there has been some disagreement in literature about whether or not large-$\eta$ constant roll solutions are attractors or are also a class of transient solutions. In this paper we show that the large-$\eta$ constant roll solutions do in fact represent transient solutions by performing stability analysis on the exact analytic (large-$\eta$) constant roll solutions.
Magnetic fields are observed at all scales in the universe, from planets all the way up to clusters of galaxies. To explain the presence of magnetic fields in the inter-cluster voids that are correlated on large scales, we need to consider the possibility of primordial magnetic fields. These fields, generated at early epochs of the universe like inflation or phase transitions, are subsequently amplified by magnetohydrodynamic evolution. In addition, the magnetic fields can be helical, with the corresponding generation processes involving parity violation; such processes can be intimately linked to baryogenesis. Working with my collaborators (Tina Kahniashvili, Axel Brandenburg, Alberto Roper Pol, Tanmay Vachaspati, and Alexander Tevzadze), we performed direct numerical simulations to model the magnetohydrodynamic turbulence affecting the evolution of these primordial fields, and study how the presence of helicity affects the evolution. We compare our results to existing limits on the strength and correlation lengths of magnetic fields at recombination from TeV blazars, and conclude that only helical magnetic fields can have the observed $\mathrm{nG}$ strength at $30\,\mathrm{kpc}$ scales.
The minimal Standard Model (SM) running of the gauge couplings gives us a hint of a Grand Unified Theory (GUT) at $M_U \sim 10^{14}$ GeV — a scale, however, too high to probe directly via collider searches. Fortunately, since the inflationary Hubble scale H can be as high as $5\times 10^{13}$ GeV $\sim M_U$, such GUT scale states can be cosmologically produced during inflation and contribute to primordial non-Gaussianity (NG). In this talk, we will explore the possibility of doing on-shell, mass-spin spectroscopy of GUT-states by studying such NG contributions in an extra-dimensional framework of orbifold GUTs.
We localize the inflaton on one of the boundaries of an extra dimension and note that the inflationary vacuum energy can readily lead to the formation of a horizon in the bulk. We will identify an interesting and optimal regime where the extra dimension is stabilized close to the onset of such a horizon and find that both the KK gravitons and KK gauge bosons can mediate observable NG — providing a direct probe of orbifold GUTs.
We consider the HL-LHC discovery potential in the 3 inverse ab data set for gluinos in the gluino-weakino associated production channel. We propose a search in the jets plus missing energy channel which exploits kinematic edge features in the reconstructed transverse mass of the gluino. We find that for squark masses in the 2 TeV range we have 5 sigma discovery potential for gluino masses in the range of 2.4 to 3 TeV, competitive with the projections for discovery potential in the gluino pair production channel.
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.
Searches for supersymmetry are a key focus of the LHC experimental program. In particular, natural SUSY models motivate third generation squarks with masses light enough to be produced at the LHC. As a result, the ATLAS experiment has a variety of analyses devoted to stop/sbottom direct production. In this talk, recent results from these searches are discussed, and the current stop/sbottom mass exclusion limits are presented in several simplified models.
Supersymmetry (SUSY) provides elegant solutions to several problems in the Standard Model,
and searches for SUSY particles are an important component of the LHC physics program. The
direct production of electroweak SUSY particles, such as sleptons, charginos, and neutralinos, is
a particularly interesting area with connections to dark matter and the naturalness of the Higgs
mass. This talk will present results from searches for electroweak SUSY partners using data
collected with the ATLAS experiment in Run 2 at the LHC. We use several different signatures
to search for direct production of electroweak particles, and interpret the results as constraints on
a variety of SUSY models.
There are many models beyond the standard model which include electroweakly interacting massive particles (EWIMPs), often in the context of the dark matter. We study the indirect search of EWIMPs using a precise measurement of the lepton pair production cross sections at future 100 TeV hadron colliders. It is revealed that this search strategy is suitable in particular for Higgsino and that the Higgsino mass up to about 850 GeV will be covered at 5 sigma level irrespective of the chargino and neutralino mass difference. We also show that the property of the observed signal, in particular its weak charges and mass, can be independently read off by using both the neutral and charged current processes.
R-parity violation introduces many viable signatures to the search for supersymmetry at the LHC. The decay of supersymmetric particles can produce leptons or jets, while removing the missing transverse momentum signal common to traditional supersymmetry searches. 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 these unusual signatures of R-parity violation and long-lived particles with the ATLAS detector.
In this talk, I will discuss the constraints on R-Parity Violating (RPV) couplings of the minimal supersymmetric standard model, using Drell-Yan differential cross sections at the LHC. Specifically, I will look at the constraints on $\lambda'LQD^c$ couplings from monolepton and dilepton data published by ATLAS. Out of the 27 $\lambda'$-couplings, we find new limits on 18 (or 19) of them, for squarks masses above 1 (or 2) TeV. These constraints are obtained by quantifying the effect of RPV on the Drell-Yan differential cross sections. I will also show that these techniques can be employed to achieve significantly stronger bounds at a high-luminosity upgrade of the LHC.
We explore the extent to which future precision measurements of the Standard Model (SM) parameters at the proposed $Z$-factories and Higgs factories may have impacts on new physics beyond the Standard Model, as illustrated by studying the Type-I two Higgs doublet model (Type-I 2HDM). We include the contributions from the heavy Higgs bosons at the tree-level and at the one-loop level in a full model-parameter space. We perform a multiple variable global fit with non-alignment and non-degenerate masses. We find that the allowed parameter ranges are tightly constrained by the future Higgs precision measurements, especially for small and large values of $\tan\beta$. Indirect limits on the masses of heavy Higgs can be obtained, which can be complementary to the direct searches of the heavy Higgs bosons at hadron colliders. We also find that the expected accuracies at the $Z$-pole and at a Higgs factory are quite complementary in constraining mass splittings of heavy Higgs bosons.
Searches for Higgs bosons in different extensions of the Standard Model (SM) are presented. These include models with additional scalar singlets, doublets, or triplets, and generic searches for models with couplings modified with respect to the SM or for non-SM Higgs boson decay channels. Results are based on data collected by the ATLAS in 2015 and 2016 at the LHC
We investigate the discovery potential for double Higgs production in a relatively overlooked $hh \to b \bar{b} W W^* \to b \bar{b} \ell^+ \ell^- + \;/\!\! \vec{P}_T$ final state. We supplement a novel kinematic method presented in Ref.[1] with jet images resulting from the $h\to b \bar b$ decay. Two $b$-quarks from the decay of the Higgs boson, are color-connected with each other. In contrast, two $b$-quarks in $t\bar t$ production (the major background) arise from the decays of top quarks, which are color-connected with initial states. Since the difference in color-flow will be reflected in the resulting hadron distributions, we utilize a Convolutional Neural Network (CNN) trained on jet images for the signal-to-background discrimination. We design a DNN architecture to successfully combine new kinematic variables and jet images. As a result, we can obtain a sizable improvement on the signal sensitivity. We discuss relative improvements at each stage and the correlations among different input variables. The proposed method can be easily generalized to the semi-leptonic channel. The $b \bar{b} W W^*$ channel would contribute to the combined analysis of double Higgs production along with the other final states.
[1] J. H. Kim, K.C. Kong, K. T. Matchev and M. Park, Probing the Triple Higgs Self-Interaction at the Large Hadron Collider, Phys.Rev.Lett. 122 (2019) no.9, 091801, [1807.11498].
I will discuss the di-Higgs production via gluon fusion within the context of Minimal Supersymmetric Standard Model (MSSM) and Next-to-Minimal Supersymmetric Standard Model (NMSSM). The calculation is based on the analytical expression of the leading order Feynman amplitudes (which includes both quark and squark loops), and therefore, both off-shell effects and interference between resonant and non-resonant contributions are accounted for. We choose the parameter space that is allowed by the current experimental constraints, and also relevant to the LHC experiments in the near future. I am going to show the parameter space where the di-Higgs production can be enhanced significantly in each case.
We study the custodial Randall-Sundrum model with two Higgs doublets localized in the TeV brane. The scalar potential is CP- conserving and has a softly broken
Z2 symmetry. In the presence of a curvature-scalar mixing term the radion that
stabilizes the extra dimension now mixes with the two CP-even neutral scalars.
A goodness of fit of the LHC data on the properties of the light Higgs is performed on the parameter space of the type-I and type-II models. LHC direct searches for heavy scalars in different decay channels can help distinguish between the radion and a heavy Higgs.
The most important signatures involve the ratio of heavy scalar decays into b quark pairs to those into Z pairs, as well as the decay of the scalar (pseudoscalar) into a Z plus a pseudoscalar (scalar).
Dark matter (DM) substructure is expected to exist over a large range of scales in our Galaxy. Its properties, such as its spatial distribution and abundance at different mass scales, can strongly correlate with the underlying particle physics properties of dark matter. Inferring DM substructure properties can thus hold the key to pinning down the particle nature of DM. In this talk, I will describe how the pattern of correlated velocities and acceleration induced due to gravitational lensing by subhalos in our Galaxy on the motions of extragalactic objects such as quasars can be used to infer the nature of substructure by directly and statistically probing the subhalo mass function. I will show how this measurement can be used to test the cold dark matter (CDM) hypothesis and distinguish it from alternative scenarios, and how this can be practically achieved with future astrometric surveys and/or radio telescopes such as the Square Kilometer Array.
The dark matter (DM) content in the local solar neighborhood is an important ingredient for direct detection experiments on Earth such as LZ, Xenon, PandaX, and searches for DM in charged cosmic ray data from PAMELA, AMS-02, DAMPE, and CALET. Traditionally, the local DM density has been estimated by analyzing the vertical motion of different ‘tracer’ stars in the solar neighborhood. These methods rely on an accurate reconstruction of the galactic potential by modeling baryonic matter as disks with different scale heights and normalizations, and approximating the collisionless DM halo by a constant DM density close to the galactic plane. However, dissipative interactions in, even a fraction of, the dark sector could lead to the formation of a thin dark disk, parametrized by its surface density and scale height, co-rotating with the baryonic disk. In this talk, we present constraints on thin dark disk parameters using the 6D phase space information of stars from the latest Gaia data release (DR2). We also determine a value of local DM density (in absence of a thin dark disk) that is consistent with those from complementary methods in the literature.
Self-interacting Dark Matter (SIDM) could have a number of striking observable effects, including modifications to the dark matter density on galactic and sub-galactic scales. Recent observations have revealed both ultra-compact and ultra-diffuse satellite dwarf galaxies within the Milky Way; this degree of diversity seems challenging to explain if the dark matter is collisionless and cold. I will show that tidal stripping of SIDM satellite halos naturally leads to a wider range of halo density profiles, potentially explaining these observations.
To solve the small scale issues in galaxies with dark matter, there are two major scenarios: self-interacting dark matter and fuzzy dark matter. The mass of the self-interacting dark matter is about GeV, and the mass of fuzzy dark matter need to be 10^{-22} eV. We propose a novel mechanism that by scattering with subdominant WIMP, the ultralight field solves the small scale issues in galaxies. In the example that we are giving, the mass region of the ultralight field is very broad, from meV to 10^{-21} eV.
If dark matter has strong self-interactions, future astrophysical and cosmological observations, together with a clearer understanding of baryonic feedback effects, might be used to extract the velocity dependence of the dark matter scattering rate. To interpret such data, we should understand what predictions for this quantity are made by various models of the underlying particle nature of dark matter. In this paper, we systematically compute this function for fermionic dark matter with light bosonic mediators of vector, scalar, axial vector, and pseudoscalar type. We do this by matching to the nonrelativistic effective theory of self-interacting dark matter and then computing the spin-averaged viscosity cross section nonperturbatively by solving the Schrodinger equation, thus accounting for any possible Sommerfeld enhancement of the low-velocity cross section. In the pseudoscalar case this requires a coupled-channel analysis of different angular momentum modes due to the structure of the effective potential experienced by the dark matter.
We describe two natural scenarios in which both dark matter weakly interacting massive particles (WIMPs) and a variety of supersymmetric partners should be discovered in the foreseeable future. In the first scenario, the WIMPs are neutralinos, but they are only one component of the dark matter, which is dominantly composed of other relic particles such as axions. (This is the multicomponent model of Baer, Barger, Sengupta and Tata.) In the second scenario, the WIMPs result from an extended Higgs sector and may be the only dark matter component. In either scenario, both the dark matter WIMP and a plethora of other neutral and charged particles await discovery at many experimental facilities. The new particles in the second scenario have far weaker cross-sections for direct and indirect detection via their gauge interactions, which are either momentum-dependent or second-order. However, they should have much stronger interactions via the Higgs. We estimate that their interactions with fermions will then be comparable to (although not equal to) those of neutralinos with a corresponding Higgs interaction. It follows that these newly proposed dark matter particles should be within the reach of emerging and proposed facilities for direct, indirect and collider-based detection.
We discuss the possibility of finding an upper bound on the lepton number violation scale using the cosmological bound on the cold dark matter relic density. We investigate a simple relation between the origin of neutrino masses and the properties of a dark matter candidate in the context of simple theories where the new symmetry breaking scale defines the lepton number violation scale, which by imposing the cosmological bounds, is found to be in the multi-TeV region. We investigate the predictions for direct and indirect detection dark matter experiments and the possible signatures at the Large Hadron Collider.
An interesting class of models posits that the dark matter is a Majorana
fermion which interacts with a quark together with a colored scalar mediator. Such a
theory can be tested in direct detection experiments, through dark matter scattering
with heavy nuclei, and at the LHC, via jets and missing energy signatures. Motivated
by the fact that such theories have spin-independent interactions that vanish at tree
level, we examine them at one loop (along with RGE improvement to resum large
logs), and find that despite its occurrence at a higher order of perturbation theory,
the spin-independent scattering searches typically impose the strongest constraints on
the model parameter space. We further analyze the corresponding LHC constraints
at one loop and find that it is important to take them into account when interpreting
the implications of searches for jets plus missing momentum on this class of models,
thus providing the corresponding complementary information for this class of models.
The ATLAS experiment has performed accurate measurements of mixing and CP violation in the neutral B mesons, and also of rare processes happening in electroweak FCNC-suppressed neutral B-mesons decays.
This talk will focus on the latest results from ATLAS, such as rare processes: B^0_s → mu mu and B^0 → mu mu, and CPV in Bs to J/psi phi.
The $R_{D^{(*)}}$ anomalies are among the longest-standing and most statistically significant hints of physics beyond the Standard Model. In this talk, we investigate future measurements at Belle II that can be used to tell apart the various new physics scenarios for these anomalies. We show that Belle II can use a number of $\tau$ asymmetry observables (forward-backward asymmetry and polarization asymmetries) which can be reconstructed at Belle II to distinguish between various possible new-physics scenarios.
The Standard Model (SM) is extended by introducing a complete vector-like fourth familyand a vector-like U(1)' gauge symmetry.This model can explain experimental values of the muon anomalous magnetic moment and anomalies for $b \to s \mu^+ \mu^-$ processes simultaneously without conflicting with the other observations, e.g. lepton flavor violating processes, CKM matrix, neutral meson mixings and so on. The U(1)' charge assignment compatible with Pati-Salam gauge group is favoredcompared to that compatible with the SO(10) gauge group in order to explain the muon anomalous magnetic moment. We will discuss observables which can be tested in future experiments.
It has been identified decades ago that the minimal potentially realistic model with the quark-lepton symmetry has the SU(4)xSU(2)xU(1) gauge structure and naturally contains both gauge and scalar leptoquarks. The model has been thoroughly studied by several authors.
We will comment on the capability of this model to accommodate the anomalous B-meson decay data. In particular, we will argue that the model allows for describing certain subsets of the anomalous experimental data, unavoidably predicting lepton flavor violating processes which will be testable at Belle II during the next years. On the other hand, the model is unable to simultaneously explain all the current B-anomalies and, thus, will be disproved if all those hints are confirmed as signals of New Physics.
Some interpretations of $R_{D^{(*)}}$ anomaly in $B$ meson decay using leptoquark models can also generate top quark decays through flavor changing neutral current (FCNC). In this work we focus on two leptoquarks, i.e. scalar $S_1$ and vector $U_1$ which are both singlet under the $SU(2)_L$ gauge group in the Standard Model (SM). We investigate their implications on top FCNC decays $t\to c \ell_i \ell_j$ at tree level and $t\to c V$ at 1-loop level, with $\ell$ being the SM leptons and $V=\gamma, Z, g$ being the SM gauge bosons. We utilize the $2\sigma$ parameter fit ranges from existing literatures and find that the branching ratios $Br(t\to c \ell_i \ell_j)$ at tree level can reach $10^{-6}\sim10^{-5}$ and 1-loop process $Br(t\to c g)$ can reach $10^{-9}\sim10^{-8}$. Some quick collider search prospects are also analyzed.
We present an anomaly-free Froggatt-Nielsen (FN) model to generate the fermion mass hierarchy and mixing based on a new horizontal gauge group. We explore two choices for this new group and the associated phenomenology.
We explored flavor universality violating models by studying dimension-six effective operators which modify the coupling between the first generation up-quarks, Higgs boson and $Z$ boson. Through the use of simulated boosted Higgs strahlung events at both the HL-LHC and HE-LHC, as well as existing ATLAS data for background estimates, projected constraints on the scale of new physics as function of the Wilson coefficient was obtained. The constraints from FCNCs to these flavor violating models and the complementarity of this study to exotic Higgs decay will also be discussed.
Strong constraints on flavor-changing neutral currents (FCNCs) naively imply that flavorful new physics must be at scales far beyond the reach of the LHC or future colliders. Assuming the new physics is flavor blind or has a Standard Model-like structure avoids these bounds but severely limits the potential phenomenology. In contrast, we present an alternative flavorful Ansatz for beyond the Standard Model physics: Spontaneous Flavor Violation (SFV). SFV allows for new physics to couple preferentially to first and second generation quarks while maintaining much of the protection from FCNCs present in the Standard Model. As an explicit example, we consider the SFV Ansatz applied to the two-Higgs doublet model. We present the distinctive phenomenology that arises in heavy charged Higgs production and light Higgs Yukawa enhancements, and emphasize the complementarity between flavor and collider physics observables.
We suggest simple ways of implementing Peccei-Quinn (PQ) symmetry to solve the strong CP problem in renormalizable SUSY SO(10) models with a minimal Yukawa sector. Realistic fermion mass generation requires that a second pair of Higgs doublets survive down to the PQ scale. We show how unification of gauge couplings can be achieved in this context. Higgsino mediated proton decay rate is strongly suppressed by a factor of $(MPQ/MGUT)^2$, which enables all SUSY particles to have masses of order TeV. With TeV scale SUSY spectrum, $p→\bar{ν}K^+$ decay rate is predicted to be in the observable range. Lepton flavor violating processes μ→eγ decay and μ−e conversion in nuclei, induced by the Dirac neutrino Yukawa couplings, are found to be within reach of forthcoming experiments.
Particle physics models with Peccei-Quinn (PQ) symmetry breaking as a consequence of supersymmetry (SUSY) breaking are attractive in that they solve the strong CP problem with a SUSY DFSZ-like axion, link the SUSY breaking and PQ breaking intermediate mass scales and can resolve the SUSY $\mu$ problem with a naturalness-required weak scale $\mu$ term whilst soft SUSY breaking terms inhabit the multi-TeV regime as required by LHC sparticle mass limits and the Higgs mass measurement. In spite of so many advantages these models have a major disadvantage in that global symmetries are incompatible with gravity and hence suffer a generic gravity spoliation problem. We present two models based on the discrete R-symmetry $\mathbf{Z}_{24}^R$-which may emerge from compactification of 10-d Lorentzian spacetime in string theory-where the $\mu$ term and dangerous proton decay and R-parity violating operators are either suppressed or forbidden while a gravity-safe PQ symmetry emerges as an accidental approximate global symmetry leading to a solution to the strong CP problem and a weak-scale/natural value for the $\mu$ term. Though there are many other solutions to the $\mu$ problem, the models based on discrete R-symmetry $\mathbf{Z}_{24}^R$ seem highly motivated. A general consideration of string theory landscape imply a mild statistical draw towards large soft SUSY breaking terms. We can extend this reasoning to the models considered here in which PQ symmetry is broken by a large negative quartic soft term. The pull towards large soft terms also pulls the PQ scale as large as possible. However, this is tempered by the cosmological requirement to avoid overproduction of mixed axion-WIMP dark matter in the early universe. Such requirements lead to an upper bound of $f_a$ $\sim$ $10^{14}$ GeV with a most probable value of $f_a$ $\sim$ $7*10^{11}$ GeV, which is well below the typical expectation that $f_a$ $\sim$ $10^{16}$ GeV from string theory.
We report on an intriguing observation that the values of all the couplings in the standard model except those related to first two generations can be understood from the IR fixed point structure of renormalization group equations in the minimal supersymmetric model extended by one complete vectorlike family with the scale of new physics in a multi-TeV range.
Models of electroweak supersymmetry with vanishing scalar masses at some high scale is well motivated as it suppresses dangerous flavor violating contributions. Therefore, loop suppressed and log enhanced gaugino mediated contribution remains the only source of scalar masses. Consequently, right handed sleptons turn out to be the lightest supersymmetric particles which is cosmologically unviable. In this work, we show that soft masses for scalar superpartners of all generations get radiative correction from supersymmetry breaking trilinear terms which are non-holomorphic in visible sector fields. This effect is most prominent for right handed sleptons and can even dominate over the usual gaugino mediated contribution, resulting in a viable spectra.
In this work, we initiate a study of continuum SUSY signatures at LHC. Since we have not seen any new physics at LHC yet, one naturally asks what if the new physics’s first sign does not comprise new resonances. Here, we try to demonstrate a scenario in the context of SUSY.
We propose that the $\gamma + {\not E}$ signal at the Belle-II detector will be a smoking gun for supersymmetry (SUSY) in the presence of a gauged $U(1)_{L_\mu - L_\tau}$ symmetry. A striking consequence of breaking the enhanced symmetry appearing in the limit of degenerate (s)leptons is the non-decoupling of the
radiative contribution of heavy charged sleptons to the $\gamma - Z^\prime$ kinetic mixing. The signal process, $e^+ e^- \rightarrow \gamma Z^\prime \rightarrow \gamma + {\not E}$, is an outcome of this ubiquitous feature. We take into account the severe constraints on gauged $U(1)_{L_\mu - L_\tau}$ models by several low-energy observables and show that any significant excess in all but the highest photon energy bin would be an undeniable signature of such heavy scalar fields in SUSY coupling to $Z^\prime$. The number of signal events depends crucially on the logarithm of the ratio of stau to smuon mass in the presence of SUSY. In addition, the number is also inversely proportional to the $e^+-e^-$ collision energy, making a low-energy, high-luminosity collider like Belle-II an ideal testing ground for this channel. This process can probe large swathes of the slepton mass ratio vs the additional gauge coupling ($g_X$) parameter space. More importantly, it can explore the narrow slice of $M_{Z^{\prime}}-g_X$ parameter space still allowed in gauged $U(1)_{L_\mu - L_\tau}$ models for superheavy sparticles.
We analyze a model of flavored gauge mediation in which the electroweak Higgs and messenger doublets are embedded in multiplets of a discrete non-Abelian symmetry. In this model, the minimal Higgs-messenger sector consistent with the 125 GeV Higgs mass is comprised of two vectorlike pairs of messenger fields. This model allows for the achievement of phenomenologically viable superpartner spectra in multiple ways, with colored superpartner masses as low as 4 TeV.
This talk will present a SUSY bi-axion model of high-scale inflation, in which the axionic/inflationary structure originates from gauge symmetry in an extra dimension. We show that local SUSY, although necessarily Higgsed during inflation, can naturally survive down to the $\sim$ TeV scale in order to resolve the electroweak hierarchy problem. This model presents an interesting interplay of tuning considerations relating the electroweak hierarchy, cosmological constant and inflationary superpotential, where maximal naturalness favors SUSY breaking near the electroweak scale after inflation. The scalar superpartner of the inflaton, the "sinflaton", can naturally have $\sim$ Hubble mass during inflation and sufficiently strong coupling to the inflaton to mediate primordial non-Gaussianities of observable strength in future 21-cm surveys. Non-minimal charged fields under the higher-dimensional gauge symmetry can contribute to periodic modulations in the CMB, within the sensitivity of ongoing measurements.
Recently machine learning methods like artificial neural networks and boosted decision trees are being used with great success in the task of event selection in collider physics data analysis, in order to improve the significance of a potential excess or the precision of a parameter measurement. But traditional classification cost functions used for training these ANNs aren't geared directly towards optimizing the quality of the analysis, and only indirectly attack the problem via the heuristic "signal is better than background". This disconnect between traditional classification goal and the goals of HEP event selection is mitigated somewhat by heuristics like choosing appropriate "working points".
In this work, we demonstrate how the output of neural networks, taken as a proxy for likelihood that an event is from the signal distribution, can be used to construct "optimal" event selectors and categorizers to maximize the expected significance of an excess. We also demonstrate the shortcomings of the "signal is better than background" heuristic (0/1 supervisory signal) for the purpose of parameter measurement, and introduce a new supervisory signal for training ANNs based on event reweighting techniques. The output from networks trained this way can again be used to construct optimal event selectors and categorizers to minimize the expected measurement uncertainty.
We perform a comprehensive study of the Higgs couplings, gauge-boson couplings to fermions and triple gauge boson vertices. We work in the framework of effective theories including the effects of the dimension-six operators contributing to these observables. We determine the presently allowed range for the coefficients of these operators via a 20 parameter global fit to the electroweak precision data, as well as electroweak diboson and Higgs production data from LHC Run 1 and 2. We also discuss and quantify the effect of keeping the terms quadratic in the Wilson coefficients in the analysis and we show the importance of the Higgs data to constrain some of the operators that modify the triple gauge boson couplings in the linear regime.
We study dimuon events in 2.11/fb of 7 TeV pp collisions, using CMS Open Data, and search for a narrow dimuon resonance with moderate mass (14-66 GeV) and substantial transverse momentum (pT). Applying dimuon pT cuts of 25 GeV and 60 GeV, we explore two overlapping samples: one with isolated muons, and one with prompt muons without an isolation requirement. Using the latter sample requires information about detector effects and QCD backgrounds, which we obtain directly from the CMS Open Data. We present model-independent limits on the product of cross section, branching fraction, acceptance, and efficiencies. These limits are stronger, relative to a corresponding inclusive search without a pT cut, by factors of as much as nine. Our "pT-enhanced" dimuon search strategy provides improved sensitivity to models in which a new particle is produced mainly in the decay of something heavier, as could occur, for example, in decays of the Higgs boson or of a TeV-scale top partner. An implementation of this method with the current 13 TeV data should improve the sensitivity to such signals further by roughly an order of magnitude.
Processes in particle physics are often described by a large number of observables that can carry information on the theory parameters of interest. This proves a challenge for traditional analysis methods, which struggle to extract all of this information. However, recently, a family of new inference techniques combining matrix element information and machine learning has been developed. MadMiner, a Python module wrapping around MadGraph 5 and Pythia 8, automates all steps required for these inference techniques: it supports almost any physics process and model, reducible and irreducible backgrounds, shower effects, detector simulation, and systematic uncertainties, without requiring any approximations on the underlying physics. We demonstrate the use of MadMiner in an example analysis of dimension-six operators.
We introduce a new approach for the global analysis of kinematic distributions, using a wavelet transformation to search for signals of new physics. Many LHC analyses search for bumps or other anomalous patterns as local deviations from a background model. Wavelets allow us to extract global information from the entire distribution, while retaining the local aspect of simple modifications. We propose a systematic visualization and analysis in terms of wavelet coefficients and show how for example bumps, bump-dip combinations, and oscillation patterns are extracted efficiently. Our package is publicly available online as the Kinematic Wavelet Analysis Kit (KWAK).
A new, strongly-coupled dark sector could be accessible to LHC searches now. We recast a vast set of existing LHC searches to determine the current constraints on (and future opportunities for) those dark meson production and decay. In some model scenarios, we find the 8 TeV same-sign lepton search strategy sets the best bound. The relative insensitivity of LHC searches, especially at 13 TeV, can be attributed mainly to their penchant for high mass objects or large missing energy. Dedicated searches would undoubtedly yield substantially improved sensitivity.
In this talk, I will talk about my recent work on the strong CP problem and the neutrino mass. We present a solution to the strong CP-problem in which the imaginary component of the up quark mass, acquires a very small, but non-vanishing value. This is achieved via a Dirac seesaw mechanism, which is also responsible for the generation of the small neutrino masses. Consistency with the observed values of the up quark mass at low energy is achieved via instanton contributions arising from QCD-like interactions. One attractive feature of the model is the non-vanishing value of the static neutron electric dipole moment strongly related with imaginary component of the up quark mass, which is naturally related with neutrino mass in our scenario. As a result, the natural nEDM in our model is within the reach of the next round of experiments.
Left-Right Symmetric Model (LRSM) is a high-energy extension of the Standard Model (SM), and provides an attractive framework to explain neutrino masses through see-saw mechanism. The scalar potential of the LRSM is much more complicated than the SM due to presence of a SU(2) bi-doublet and left \& right-handed weak isospin triplets in the model. We derive the analytic conditions for vacuum stability in the LRSM by requiring the tree-level potential to be bounded from below. We then discuss some phenomenological consequences.
We assess the sensitivity of the LHC, its high energy upgrade, and a prospective
100 TeV hadronic collider to the Dirac Yukawa coupling of the heavy neutrinos in
left-right symmetric models (LRSMs). We focus specifically on the trilepton final
state in regions of parameter space yielding prompt decays of the right-handed
gauge bosons ($W_R$) and neutrinos ($N_R$). In the minimal LRSM, the Dirac Yukawa
couplings are completely fixed in terms of the mass matrices for the heavy and
light neutrinos. In this case, the trilepton signal provides a direct probe of the Dirac
mass term for a fixed $W_R$ and $N_R$ mass. We find that while it is possible to discover
the $W_R$ at the LHC, probing the Dirac Yukawa couplings will require a 100 TeV pp
collider. We also show that the observation of the trilepton signal at the LHC would
indicate the presence of a non-minimal LRSM scenario.
A qualitatively new search strategy for multi-lepton searches for heavy neutrinos at hadron colliders is presented. The analysis relies on an unusual (dynamic) implementation of a jet veto, one that discriminates on an event-by-event basis, and is applicable to searches for other new, colorless particles, e.g., smuons and doubly charged scalars. We show that the sensitivity to electroweak and TeV-scale heavy neutrinos at the CERN Large Hadron Collider can be improved by an order of magnitude, and can thus compete with dedicated flavor experiments. Prospects at proposed collider facilities are also presented.
We consider a gauged U(1) B−L (Baryon-minus-Lepton number) extension of the Standard Model (SM), which is anomaly-free in the presence of three Right-Handed Neutrinos (RHNs). Associated with the U(1)B−L symmetry breaking the RHNs acquire their Majorana masses and then play the crucial role to generate the neutrino mass matrix by the seesaw mechanism. Towards the experimental confirmation of the seesaw mechanism, we investigate a RHN pair production through the U(1)B−L gauge boson (Z′) at the 250 GeV International Linear Collider (ILC). The Z′ gauge boson has been searched at the Large Hadron Collider (LHC) Run-2 and its production cross section is already severely constrained. The constraint will become more stringent by the future experiments with the High-Luminosity upgrade of the LHC (HL-LHC). We find a possibility that even after a null Z′ boson search result at the HL-LHC, the 250 GeV ILC can search for the RHN pair production through the final state with same-sign dileptons plus jets, which is a `smoking-gun' signature from the Majorana nature of RHNs. In addition, some of RHNs are long-lived and leave a clean signature with a displaced vertex. Therefore, the 250 GeV ILC can operate as not only a Higgs Factory but also a RHN discovery machine to explore the origin of the Majorana neutrino mass generation, namely the seesaw mechanism.
Motivated by the null results of the BSM searches in the post-Higgs era of the LHC, our current approach is to look for new physics shifting from theory driven search strategies to signature driven ones. One possible direction might come from investigating the long-lived particles (LLP’s) present in different theoretical scenarios through the “Lifetime frontier”. We discuss a non-sterile right-handed neutrino model consisting of EW scale Majorana masses having signals with large displaced vertices arising in both the fermion and scalar sectors. The characteristic features in this model, the displaced vertices, i.e several charged tracks originating from a position separated from the proton interaction point has to be greater than a mm and can be as long as order of centimeters. These events originating from the decays of the mirror fermions produce promising signatures at the LHC environment due to the low associated backgrounds. We discuss the experimental implications and possible search strategies in this framework and LHC’s potential to unravel these underlying events.
Heavy neutrinos are essential ingredients in the type-I seesaw mechanism for neutrino masses. Mixing and CP violation in the heavy neutrino sector therefore not only translate into neutrino oscillation parameters but also play an important role in generating the observed baryon asymmetry of the universe via leptogenesis. We show that future hadron colliders can directly access these mixing angles and CP phases in the heavy neutrino sector if type-I seesaw is embedded in a TeV-scale left-right model, by measuring the charge asymmetries in same-sign dilepton signals, e.g. $e^+ e^+$ versus $e^- e^-$, arising from $W_R$-mediated heavy neutrino production and subsequent decays. This provides a new way to test low-scale leptogenesis at future colliders.
Neutrinos are massless in the Standard Model (SM), therefore, to explain neutrino oscillation, physics beyond SM is needed. The type-II seesaw mechanism is one of the mechanisms that can naturally generate neutrino masses. In this talk, I will discuss phenomenology of the type-II seesaw scalar triplet model at the 100$\,$TeV $pp$ collider, focusing on: (1) model discovery; (2) Higgs portal parameter determination, which is relevant for electroweak baryogenesis.
The conventional misalignment mechanism can explain axion dark matter only in a limited mass range and face various difficulties for vector dark matter that we refer to as dark photons. We propose new dark matter production mechanisms for axions and dark photons via parametric resonance and tachyonic instability, respectively. These ideas expand the parameter space to the regions of interest for the extensive experimental searches for dark matter. Other potential signatures include dark matter ultracompact minihalos, warm dark matter, and gravitational waves.
Ultra-light scalar theories with repulsive self-interactions admit boson stars with large compactness. I will show the origin of the maximum mass of spherically symmetric stable boson stars, which manifests only in the full equations of motion in curved space-time, but not in the approximated Schrödinger-Newton equations. The backreaction of the curvature on the scalars acts as an additional source of attraction and can overcome the repulsion, resulting in a maximum star mass and compactness. In addition, I will show that the potential in a UV completed particle physics model of light scalar dark matter is generally more complicated than the widely used \phi^4 interaction, which shows up as a modified mass profile relevant for LIGO detection. In the context of LISA, EMRI involving a boson star can be distinguished by the small mass of the infalling object, as well as tidal disruption. Using LISA's sensitivity, I show the parameter space of the underlying scalar theory where the infalling boson stars can be distinguished from all other compact objects.
Exotic compact objects such as primordial black holes, boson star, etc., are theoretically predicted to exist and can make interesting dark matter candidates,
yet with no definitive observational evidence for their existence. This talk will
discuss the method of using gravitational waves from the extreme mass ratio inspiral, formed by an ECO and a supermassive black hole in the center of each galaxy as a probe of the ECOs. The corresponding gravitational waves can be detected by future space-based interferometer gravitational wave detectors and
the mass of the ECO can be determined very precisely. Aside from gravitational wave signals, possible electromagnetic counterparts for some ECOs, like boson stars, will be discussed.
Primordial black holes (PBHs) with a mass from $10^{-16}$ to $10^{-11}\,M_\odot$ may comprise 100% of dark matter. Due to a combination of wave and finite source size effects, the traditional microlensing of stars does not probe this mass range. In this talk, we point out that X-ray pulsars with higher photon energies and smaller source sizes are good candidate sources for microlensing for this mass window. Among the existing X-ray pulsars, the Small Magellanic Cloud (SMC) X-1 source is found to be the best candidate because of its apparent brightness and long distance from telescopes. We have analyzed the existing observation data of SMC X-1 by the RXTE telescope (around 10 days) and found that PBH as 100% of dark matter is close to but not yet excluded. Future longer observation of this source by X-ray telescopes with larger effective areas such as AstroSat, Athena, Lynx, and eXTP can potentially close the last mass window where PBHs can make up all of dark matter.
We show how a simple dissipative dark sector can form exotic compact objects that vary in size from a few to millions of solar masses. These exotic compact objects may be detected and their properties measured at new high-precision astronomical observatories, giving insight into the particle nature of the dark sector without the requirement of non-gravitational interactions with the visible sector.
Mirror sectors -- hidden sectors that are approximate copies of the Standard Model -- are a generic prediction of many models, notably the Mirror Twin Higgs model. Such models can have a rich cosmology and many interesting detection signatures beyond the realm of colliders. In this talk, I will focus on the possibility that mirror matter can form stars which undergo mirror nuclear fusion in their cores. I will discuss the mechanisms by which these objects can emit Standard Model light and estimate their luminosity and prospects for their detection.
"Dark quark nuggets", a lump of dark quark matter, can be produced in the early universe for a wide range of confining gauge theories and serve as a macroscopic dark matter candidate. The two necessary conditions, a nonzero dark baryon number asymmetry and a first-order phase transition, can be easily satisfied for many asymmetric dark matter models and QCD-like gauge theories with a few massless flavors. For confinement scales from 10 keV to 100 TeV, these dark quark nuggets with a huge dark baryon number have their masses vary from $10^{23}~\mathrm{g}$ to $10^{-7}~\mathrm{g}$ and their radii from $10^{8}~\mathrm{cm}$ to $10^{-15}~\mathrm{cm}$. Such macroscopic dark matter candidates can be searched for by a broad scope of experiments and even new detection strategies. Specifically, we have found that the gravitational microlensing experiments can probe heavier dark quark nuggets or smaller confinement scales around 10 keV; collision of dark quark nuggets can generate detectable and transient electromagnetic radiation signals; the stochastic gravitational wave signals from the first-order phase transition can be probed by the pulsar timing array observations and other space-based interferometry experiments; the approximately massless dark mesons can behave as dark radiation to be tested by the next-generation CMB experiments; the free dark baryons, as a subcomponent of dark matter, can have direct detection signals for a sufficiently strong interaction strength with the visible sector.
The conjectured bound state of uuddss in color-spin-flavor singlet can be a stable and compact particle, the sexaquark. Such a particle formed from QCD plasma in the early universe explains the observed dark matter abundance and can potentially resolve the 7Li puzzle. We will argue that a stable sexaquark may live in a rather wide mass window, either above two nucleon mass or below, because of three reasons: 1) the color-spin-flavor constraints, 2) the doubly-weak nature of the transition, and 3) the spatial suppression. Experimental limits on the spatial suppression from the SNO experiment will be discussed.
Recently LHCb announced the exciting discovery of direct CP asymmetry in D0 decays to K-pairs and pion pairs around 15X10^-4. It is extremely difficult to do reliable calculations for the expectations from the SM for these asymmetries because of large non-perturbative effects. However, a mechanism will be proposed to helps us understand roughly the size of the asymmetry and the key idea readily leads to several testable predictions. Moreover, even though the original amplitudes for D^0 => h^+ h^- are extremely difficult to handle on the lattice using known techniques, many features of the idea being proposed here may well be amenable to lattice simulations.
One of the conditions for creating a matter-dominated Universe is presence of interactions that differentiate between matter and anti-matter. Properties of such interactions can be probed at particle accelerators by studying decay patters of produced particles. On March 21, one of the CERN's experiments, the LHCb, announced observation of CP-violation in the decays of particles containing charm quark. I discuss theoretical implications of this important discovery, and why it took experimentalists such a long time to make this observation. I will also discuss why it would take even longer for theorists to discern it.
Associated production of vector boson with quarkonia is a key observable for understanding the quarkonium production mechanisms, including the separation of single and double parton scattering components. This talk will present the latest differential measurements from ATLAS of associated-quarkonium production. In addition, recent results on heavy flavour production measurements are reported in the Bu and Bc systems.
We develop a systematic treatment of the heavy-flavor hadroproduction in general-mass variable flavor number scheme (GM-VFNS). By following the idea of Simplified-ACOT-?chi scheme in the deep inelastic scattering (DIS), we categorize the open heavy-flavor diagrams into Flavor Excitation (FE) and Flavor Creation (FC). The overlapped diagrams are subtracted by the collinear splitting in order to avoid double-counting. The Flavor Creation terms can be extracted from Fixed Flavor Number Scheme (FFNS), while the Flavor Excitation terms and Subtraction (SB) terms involve the initial heavy-flavor parton scattered by another light parton (light quark or gluon). We introduce the massive phase space for the FC and SB, which accounts for the threshold effect of massive heavy quark. We dub this novel scheme as S-ACOT-MPS scheme. The massive phase space regulates the singular behavior for pT->0, which stabilizes the cancellation between FE and SB in this limit and leads a smooth transition to the FFNS as a result. Our numerical results provide a good agreement with the LHCb measurement of B-meson? production.
Recent results of the LHCb experiment related to b&c hadron spectroscopy including exotic hadron states.
Doubly heavy baryons and singly heavy antimesons are related by heavy quark-diquark (HQDQ) symmetry because in the $m_Q \to \infty$ limit the light degrees of freedom in both hadrons are expected to be in identical configurations. Hyperfine splittings of the ground states in both systems are nonvanishing at $O(1/m_Q)$ in the heavy quark mass expansion and HQDQ symmetry relates the hyperfine splittings in the two sectors. It was expected that corrections to this prediction would scale as $O(1/m_Q^2)$. In this paper, working within the framework of Non-Relativistic QCD (NRQCD), we point out the existence of an operator that couples four heavy quark fields to the chromomagnetic field with a coefficient that is enhanced by factor from Couloumb exchange. This operator gives corrections to doubly heavy baryon hyperfine splittings that scale as $1/m_Q^2 \times \alpha_S/r$, where $r$ is the separation between the heavy quarks in the diquark. This corrections can be calculated analytically in the the extreme heavy quark limit in which the potential between the quarks in the diquark is Coulombic. In this limit the correction is $O(\alpha_s^2/m_Q)$ and comes with a small coefficient. For values of $\alpha_s$ relevant to doubly charm and doubly bottom systems the correction to the hyperfine splittings in doubly heavy baryons is only a few percent or smaller.
If the $X(3872)$ is a weakly bound charm-meson molecule, it can be produced in $e^+ e^-$ annihilation by the creation of $D^{*0} \bar D^{*0}$ from a virtual photon followed by the rescattering of the charm-meson pair into the $X$ and a photon. A triangle singularity produces a narrow peak in the cross section for $e^+ e^- \to X \gamma$ about 2.2 MeV above the $D^{*0} \bar{D}^{*0}$ threshold. We predict the absolutely normalized cross section in the region near the $D^{*0} \bar D^{*0}$ threshold. The peak from the triangle singularity may be observable by the BESIII detector.
The rare inclusive decay $\bar{B}\rightarrow X_s\gamma$ is an important probe of physics beyond the standard model. The largest uncertainty on the decay rate and CP asymmetry comes from resolved photon contributions. They first appear at order $1/m_b$ in the heavy quark expansion and arise from operators other than $Q_{7\gamma}$. One of the three leading contributions in the heavy quark expansion, $Q_1^q-Q_{7\gamma}$ is described by a non-local function whose moments are related to HQET parameters. We use recent progress in our knowledge of these parameters to better constrain the resolved photon contribution to $\bar{B}\rightarrow X_s\gamma$ total rate and CP asymmetry.
The scattering amplitude for massive spin-2 particles at high energies suffers from growth proportional to energy to the tenth power. In this talk we discuss the origin of this bad high-energy behavior, how it must necessarily be mitigated in the case where the massive modes arise from a compactified theory of gravity, and we outline how the cancellations necessary to reduce this growth to energy-squared arise in compactified five-dimensional theories of gravity. We give a physical interpretation of these results, and we compare with the parallel case of massive spin-1 particle scattering in compactified five-dimensional gauge theories.
We report the results of computations of the scattering amplitudes for massive spin-2 Kaluza-Klein particles in compactified five-dimensional theories of gravity. We demonstrate that different classes of diagrams individually grow as energy to the tenth power as expected, but that intricate cancellations among different diagrams reduce this growth to energy-squared. We show that these cancellations occur in both toroidal and AdS (Randall-Sundrum) compactifications of five-dimensional gravity, though the energy scale controlling the rate of growth is rather different in these two cases.
Infrared divergences have long been heralded to cancel in sufficiently inclusive cross sections, according to the famous Kinoshita-Lee-Nauenberg (KLN) theorem. The theorem states that summing over all initial and final states with energies in some compact energy window around a reference energy $E_0$ guarantees finiteness. While well-motivated, this theorem is much weaker than necessary: for finiteness, one need only sum over initial or final states. Moreover, the cancellation generically requires the inclusion of the forward scattering process. We provide some examples showing the importance of this revised understanding. The process $e^+ e^- \to Z$ can be made IR finite at next-to-leading order in three ways: One can sum over either initial or final states with a finite number of photons if forward scattering is included, as dictated by the KLN theorem, or use a third way of summing over certain initial and final states with an arbitrary number of extra photons. We furthermore discuss why the rate for γγ to scatter into photons alone is infrared divergent but the rate for γγ to scatter into photons or charged particles is finite. This new understanding sheds light on the importance of including degenerate initial states in physical predictions, the relevance of disconnected Feynman diagrams, the importance of dressing initial or final-state charged particles, and the quest to properly define the S matrix.
We propose to construct effective field theory in terms of on-shell scattering amplitudes, rather than operators consisting of quantum fields. Using the methods like recursion relation and unitarity cut, most of the physical observables can be computed based on a set of on-shell amplitudes that we call the amplitude basis. We establish the correspondence between the amplitude basis and the operator basis in the old style effective field theory. We also reproduce the operator counting at dimension 5 and 6 for the Standard Model Effective Field Theory.
Soft-Collinear Effective Theory (SCET) for gravity has recently been developed at leading and next-to-leading powers of a small parameter, $\lambda$. Being an effective theory, SCET for gravity is halfway between full theory of gravity (below Planck scale) and gravity scattering amplitudes. This reveals many interesting properties of gravity amplitudes which are obscure in full theory and usually need lengthy calculations or ingenious tricks to realize, such as soft graviton theorem and absence of collinear IR divergences at the leading power. More importantly, SCET for gravity significantly simplifies calculation of scattering amplitudes that include gravitons. Reparametirization invariance (RPI) is a redundancy of SCET for gravity and it arises in two ways. First, there is redundancy in choosing two reference unit vectors for defining light cone coordinates of each collinear sector. The choice of these reference vectors is not unique and physics should be independent of them. However, since effective operators in the Lagrangian depend explicitly on these vectors, the invariance means that different operators at the same power of $\lambda$ and different powers would be canceling each others transformations. Thus their Wilson coefficients can be related to each other and this makes matching to full theory much easier. Second type of RPI is our freedom in choosing the $\lambda^2$ component of collinear momentum and soft momentum. In this talk I will be presenting our findings on RPI in SCET for gravity as well as the structure of NNLP operators.
The calculation of particle decay rates typically proceeds by an S-matrix approach in Minkowski spacetime. While such an approach is often highly effective, it fails, in general, when performing calculations in dynamic spacetimes since the S-matrix necessitates global energy conservation which is not present in an expanding universe, like ours. I will describe how the decay law of scalar particles decaying during the radiation dominated epoch of a standard cosmological model can be obtained by introducing an adiabatic approximation valid for degrees of freedom with typical wavelengths much smaller than the particle horizon at a given time. Furthermore, this decay law is calculated, treating the cosmological expansion consistently, through the non-perturbative Wigner-Weisskopf method adapted for cosmology. I will discuss both scalar to scalar and scalar to fermion (with Yukawa couplings) decays within this framework highlighting how the effects of cosmic expansion, such as cosmic redshift and the confluence of time-dependent particle frequencies with a renormalizable theory, lead to salient differences from the usual Minkowski spacetime results.
The evidence for dark matter is overwhelming, but its nature is unknown. Dark matter may be the magnetic monopoles of a hidden sector, which acquire small coupling to the visible photon through kinetic mixing. When the hidden sector U(1) is broken, the monopoles confine, connected by a tube of magnetic flux. These flux tubes give rise to phase shifts in Aharanov-Bohm experiments. I show the existing experimental constraints on this scenario, and explain how to search for dark matter with Aharanov-Bohm type detectors.
Recent studies show that there is tension between the de Sitter swampland conjectures proposed by Obeid, et al. and inflationary cosmology. In this paper, we consider an alternative to inflation, `tachyacoustic' cosmology, in light of swampland conjectures. In tachyacoustic models, primordial perturbations are generated by a period of superluminal sound speed instead of accelerating expansion. We show that realizations of tachyacoustic Lagrangians can be consistent with the de Sitter swampland conjectures, and therefore can in principle be consistent with a UV-complete theory. We derive a general condition for models with c_S>1 to be consistent with swampland conjectures.
Exotic decays of the 125 GeV Higgs boson can offer an alternative avenue to probe physics beyond the standard models such as two-Higgs-doublet model extended with a complex scalar singlet (2HDM + S) and next-to-minimal super-symmetric model (NMSSM). Light bosons with masses less than half of the Higgs boson mass are probed in final states containing two muons and two b quarks, or two muons and two tau leptons. The latest results from searches for these decays at the CMS will be presented.
Singlet extensions of the Standard Model (SM) provide unique test of the paradigm of strongly first order electroweak phase transition (EWPhT). We study the real singlet extension of the SM with spontaneous $Z_2$-breaking, and its impact on the strength of the electroweak phase transition as well as the corresponding phenomenology. We find various phase transition patterns rendering a strongly first order EWPhT. After including the corresponding one loop zero temperature and thermal corrections, we identify the regions of parameter space with a strong EWPhT, that require a rather light real scalar. Phenomenologically, Higgs exotic decays, together with constraints from precision measurement of the Higgs properties at the LHC, provide the ultimate probe of such an SM extension.
We investigate the collider signature of the real singlet extension of the standard model.
A definitive correlation exists between the strength of the phase transition and the trilinear coupling of the Higgs to two singlet-like scalars, and hence between the phase transition and non-resonant scalar pair production involving the singlet at colliders.
We study the prospects for observing these processes at the high luminosity LHC, focusing particularly on the associated production of singlet and the SM Higgs.
Standard model is successful in explaining Higgs physics, however new physics beyond the standard model may yet be expected. We study how the inclusion of real singlet scalar and dimension 5 operators effect SM Higgs physics. We do this by studying the deviations of the total width and branching ratios of the Higgs from the SM predictions. We also study the limit on scalar mixing angle and Wilson coefficients by a fit to the ATLAS/CMS Higgs signal strength.
We present a dedicated complementarity study of gravitational wave and collider
measurements of the simplest extension of the Higgs sector: the singlet scalar augmented Standard
Model. We study the following issues: (i) the electroweak phase transition patterns admitted by the model, and the proportion of parameter space for each pattern; (ii) the regions of parameter space that give detectable gravitational waves at future space-based detectors; and (iii) the current and future collider measurements of di-Higgs production, as well as searches for a heavy weak
diboson resonance, and how these searches interplay with regions of parameter space that exhibit strong gravitational wave signals. We carefully investigate the behavior of the normalized energy released during the phase transition as a function of the model parameters, address subtle issues pertaining to the bubble wall velocity, and provide a description of different fluid velocity profiles.
On the collider side, we identify the subset of points that are most promising in terms of di-Higgs and weak diboson production studies while also giving detectable signals at LISA, setting the stage for future benchmark points that can be used by both communities.
Although the discovered scalar with a mass of 125 GeV appears to have the properties of the Standard Model Higgs, it remains a possibility that it belongs to an enlarged scalar sector containing other Higgs bosons waiting to be discovered. Motivated by the recent CMS and ATLAS diphoton excesses near 95 GeV, we consider a Type-I two-Higgs-doublet model in regions of high fermiophobia allowing for an enhancement in the γγ rate for scalars lighter than the Standard Model Higgs. We fix one CP-even neutral scalar to be SM-like with a mass of 125 GeV and consider separately the other CP-even neutral scalar or the CP-odd neutral pseudoscalar as the source of the observed signal excess. In both instances, we explore the parameter space and identify regions surviving experimental and theoretical constraints. We also consider the strength of the electroweak phase transition within the model and find regions where the transition is strongly first order, allowing for electroweak baryogenesis to explain the observed baryon asymmetry.
An exact spacetime parity replicates the $SU(2) \times U(1)$ electroweak interaction, the Higgs boson $H$, and the matter of the Standard Model. This "Higgs Parity" and the mirror electroweak symmetry are spontaneously broken at scale $v' = \langle{H'}\rangle \gg \langle{H}\rangle$, yielding the Standard Model below $v'$ with a quartic coupling that essentially vanishes at $v'$: $\lambda_{SM}(v') \sim 10^{-3}$. The strong CP problem is solved as Higgs parity forces the masses of mirror quarks and ordinary quarks to have opposite phases. Dark matter is composed of mirror electrons, $e'$, stabilized by unbroken mirror electromagnetism. These interact with Standard Model particles via kinetic mixing between the photon and the mirror photon, which arises at four-loop level and is a firm prediction of the theory. Physics below $v'$, including the mass and interaction of $e'$ dark matter, is described by $\textit{one fewer parameter}$ than in the Standard Model. The allowed range of $m_{e'}$ is determined by uncertainties in $(\alpha_s, m_t, m_h)$, so that future precision measurements of these will be correlated with the direct detection rate of $e'$ dark matter, which, together with the neutron electric dipole moment, will probe the entire parameter space.
We explore the implications of recent results relating the Dirac CP-violating phase to predicted and measured leptonic mixing angles within a standard set of theoretical scenarios in which charged lepton corrections are responsible for generating a non-zero value of the reactor mixing angle. We employ a full set of leptonic sum rules as required by the unitarity of the lepton mixing matrix, which can be reduced to predictions for the observable mixing angles and the Dirac CP-violating phase in terms of model parameters. These sum rules are investigated within a given set of theoretical scenarios for the neutrino sector diagonalization matrix for several known classes of charged lepton corrections. The results provide explicit maps of the allowed model parameter space within each given scenario and assumed form of charged lepton perturbations.
We present a novel framework that provides an explanation to the long-standing excess of electronlike events in the MiniBooNE experiment at Fermilab. We suggest a new dark sector containing a dark neutrino and a dark gauge boson, both with masses between a few tens and a few hundreds of MeV. Dark neutrinos are produced via neutrino-nucleus scattering, followed by their decay to the dark gauge boson, which in turn gives rise to electronlike events. This mechanism provides an excellent fit to MiniBooNE energy spectra and angular distributions. We propose here to use this fact to connect the generation of neutrino masses to a light dark sector, charged under a new U(1)D dark gauge symmetry. We introduce the minimal number of dark fields to obtain an anomaly free theory with the spontaneous breaking of the dark symmetry and obtain automatically the inverse seesaw Lagrangian. In addition, the so-called μ-term of the inverse seesaw is dynamically generated and technically natural in this framework.
In Zee model, radiative neutrino mass model, new scalar bosons are added that can induce significant nonstandard neutrino interactions (NSI). In this talk, I will present our results of a comprehensive analysis of NSI. Diagonal NSIs of order several percents are found to be possible that utilizes charged scalars.
Non-standard neutrino interactions (NSI) can interfere with measurements of neutrino oscillation parameters at long-baseline experiments, in particular making determination of $\delta_{13}$ ambiguous. Measurements at different baselines or energies may be combined to improve this situation, but it can be difficult to see the influence of individual parameters and determine when degeneracies may exist or be broken. In this talk I will show how the relationship between underlying parameters, degeneracies and their breaking may be represented in a convenient way in biprobability space. An application of particular interest is the experimental hints suggesting $\delta_{13} \sim -\pi/2$, which could be consistent with nonzero NSI but the absence of CP violation. I'll also present on-going work that applies this to understand the reach of upcoming experiments in distinguishing models.
X-ray observations of clusters and galaxies have detected an unexplained X-ray emission line around 3.5 keV. This line has been the subject of many recent works due to its potential explanation as due to decaying dark matter. In particular, sterile neutrinos with a mass of 7 keV and mixing angles of $\sim10^{−10}$ provide a good fit to the data. I discuss recent work in which we exploit the fact that the Milky Way halo is as bright in dark matter decay as previous targets but has significantly reduced backgrounds. Furthermore, all X-ray observations look through the halo, so there is an abundance of available data. In particular, we used over 30 Ms of XMM-Newton observations of the ambient dark matter halo to search for evidence of this line. We report the strongest limits to-date on the lifetime of dark matter in this mass range and strongly disfavor the possibility that the 3.5 keV line originates from dark matter decay.
We will demonstrate the usage of GDML within GEANT4 for building and optimizing shielding for germanium detectors used by MINER, which is a current experiment aimed at detecting coherent elastic neutrino-nucleus scattering at a few meter baseline from a 1MW nuclear reactor. We will discuss preliminary comparisons with background data recently obtained by a germanium detector at the reactor site where MINER operates.
We revisit calculations of invisible widths of heavy mesons in the standard model, which serve as benchmarks for the studies of production of light, long-lived neutral particles in heavy meson decays. We challenge the common assumption that in the standard model these widths are dominated by meson decays into a two-neutrino final state and prove that they are dominated by decays into fourneutrino final states. We show that current estimates of the invisible widths of heavy mesons in the standard model underestimate the effect by orders of magnitude. We examine currently available experimental data on invisible widths and place constraints on the properties of dark photons. We also comment on the invisible widths of the kaons.
I will discuss the collider and dark matter phenomenology of models of portal matter which is responsible for generating the kinetic mixing between the SM and the dark photon at 1-loop. Both top-down (based on the group SU(8)) and bottom-up model building approaches will be discussed.
We explore signals of two Higgs bosons and missing energy at the LHC. Such a signal is characteristic of models for dark matter or other secluded particles that couple to the standard model through scalar mediators. I discuss our search strategy for these new particles, based on their decay topology into a final state with two b-jet pairs and missing transverse energy. The di-Higgs channel is competitive with other missing energy searches and provides a new opportunity to find hidden particles at the LHC.
In Higgs portal models of fermion dark matter, scalar couplings are unavoidably suppressed by strong bounds from direct detection experiments. As a consequence, thermal dark matter relics must coexist with mediators in a compressed spectrum of dark particles. Small couplings and small mass splittings lead to slow mediator decays, leaving signatures with displaced vertices or disappearing tracks at colliders. We perform a comprehensive analysis of long-lived mediators at the LHC in the context of a minimal dark matter model with a naturally small Higgs portal, also known as the wino-bino scenario in supersymmetry. Existing searches for disappearing charged tracks and displaced hard leptons already exclude tiny portal couplings that cannot be probed by current direct and indirect detection experiments. For larger portal couplings, we predict new signatures with displaced soft leptons, which are accessible with run-II data. Searches for displaced particles are sensitive to weakly coupling mediators with masses up to the TeV scale, well beyond the reach of prompt signals.
Dynamical Dark Matter (DDM) is an alternative framework for dark-matter physics in which the dark sector consists of large ensembles of dark states which exhibit a broad range of masses and lifetimes. While some of the states in this ensemble must be sufficiently long-lived that they contribute to the dark-matter abundance at present time, other states in the ensemble may have far shorter lifetimes. These latter states could give rise to observable signals at dedicated experiments such as the proposed MATHUSLA detector --- a detector capable of resolving the decay signatures of long-lived particles (LLPs) with a broad range of masses and lifetimes. In this talk, I examine the discovery reach of the MATHUSLA detector within the parameter space of DDM scenarios and demonstrate that MATHUSLA may be capable of providing direct confirmation of certain unique aspects of the DDM framework which might be difficult to probe in other ways.
A preponderance of astrophysical and cosmological evidence indicates that the universe contains not only visible matter but also dark matter. In order to suppress the couplings between the dark and visible sectors, a standard assumption is that these two sectors communicate only through a mediator. In this talk we make a simple but important observation: if the dark sector contains multiple components with similar quantum numbers, then this mediator also necessarily gives rise to dark-sector decays, with heavier dark components decaying to lighter components. This in turn can even give rise to relatively long dark decay chains, with each step of the decay chain also producing visible matter. The visible byproducts of such mediator-induced decay chains can therefore serve as a unique signature of such scenarios. In order to examine this possibility more concretely, we examine a scenario in which a multi-component dark sector is connected through a mediator to Standard-Model quarks. We then demonstrate that such a scenario gives rise to multi-jet collider signatures, and we examine the properties of such jets at both the parton and detector levels. Within relatively large regions of parameter space, we find that such multi-jet signatures are not excluded by existing mono-jet and multi-jet constraints. Such "jet avalanches" therefore represent a potential discovery route for multi-component dark sectors.
Extensions of the Standard Model are often highly constrained by cosmology. The presence of new states can dramatically alter observed properties of the universe by the presence of additional matter or entropy. Especially if those new states exist near the weak scale and thermal contact brings new particles into equilibrium. Without a means to deposit this energy into the SM, often these scenarios are excluded. Scenarios of ''neutral naturalness'' especially, such as the Twin Higgs often suffer from this. However, the Portalino, a singlet fermion that marries gauge neutral fermion operators, can naturally help. Unfortunately, since the third neutrino mixing angle predicted in this scenario $|U_{\tau n}|\sim\mathcal{O}(v_h/f)$ is tightly constrained by the low energy experiments, it involves more concerns in model building. In this talk, based on the Portalino formalism I will show two simple extensions of the minimal Twin Higgs model, say the weak solution and the strong solution, to evade the aforementioned constraints. In the weak solution, an additional scalar $SU(2)_L$ doublet is introduced in each sector so that $U_{\tau n}$ is suppressed by the extra mass term of twin leptons. Meanwhile, flavor violating neutrino mass matrix is generated through the Zee mechanism at one-loop level in the SM sector. Alternatively, the strong solution lifts the twin particle masses via the vacuum expaction values of twin leptoquark and diquark. In this approach, both of the baryon number and strong gauge symmetry are spontaneously broken in the hidden sector while are preserved in the visible one. The collider signatures of this model include the leptoquark and diquark single/pair productions and decays which might be captured within the range of LHC.