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PASCOS 2022, the 27th International Symposium on Particles, Strings and Cosmology, will take place on July 25-29, 2022. The aim of the conference is to review recent progress in particle physics, astroparticle physics, string theory and cosmology, with particular emphasis on their interconnections. The symposium is a platform for researchers to report and discuss what has been learned and what might show up in the next few years. Topics will include, for example, new physics at LHC, gravitational waves, neutrinos, dark matter and non-accelerator probes of new physics, string theory and new results in cosmology.
The conference includes invited plenary talks as well as parallel sessions. We particularly welcome and encourage the participation of early-career researchers.
PASCOS 2022 will be hosted in-person at the Max-Planck-Institut für Kernphysik (MPIK, Max Planck Institute for Nuclear Physics) in Heidelberg, Germany.
We present a class of models in which dark matter is composed of the composite states of a strongly coupled hidden sector. The hidden sector interacts with the standard model through the neutrino portal, allowing the relic abundance of dark matter to be set by annihilation into final states containing neutrinos. The coupling to the hidden sector also leads to the generation of neutrino masses through the inverse seesaw mechanism, with composite hidden sector states playing the role of the singlet neutrinos. We focus on the scenario in which the hidden sector is conformal in the ultraviolet, and the compositeness scale lies at or below the weak scale. We construct a holographic realization of this framework based on a five-dimensional warped geometry and study its phenomenology.
Sub-GeV thermal relic dark matter typically requires the existence of a light mediator particle. We introduce the light two-Higgs-doublet portal, illustrated by a minimal UV-complete model for sub-GeV DM with kinematically forbidden annihilations into leptons.
All new physics states in this scenario lie at or below the electroweak scale, affecting Higgs physics, the muon anomalous magnetic moment and potentially neutrino masses. Observation of radiative dark matter annihilation by future MeV gamma-ray telescopes would be key to identify the scenario.
Multipartite dark matter (DM) frameworks offer interesting phenomenology like co-annihilation, semi-annihilations, DM conversions etc to address correct relic density but avoid stringent direct search limits. We explore possible signatures of multiparticle DMs at collider via distorted missing energy, missing transverse momentum, missing mass distributions in leptonic signals and discuss conditions where such distortions can be statistically significant to infer the presence of multipartite DM framework. We also discuss advantage of an electron positron machine over the on-going LHC in doing so, where beam polarisation play a crucial role. We also touch upon possibilities with mono-X signal, where such distinctions are harder, but possible.
We study the relic abundance of stable particles from a generic dark sector in the presence and absence of initial dark asymmetries, and our results show that abundances are expected to be of similar magnitude, i.e. multi-component dark matter is quite natural. We first discuss the different possibilities for stabilizing multi-component dark matter and then analyze the final relic abundances of the symmetric and asymmetric dark matter components in the presence of unavoidable conversions between dark matter states. We find an exponential dependence of the asymmetries on annihilation and conversions for the heavier components. We conclude that having similar symmetric and asymmetric components is a quite natural outcome of scenarios with several stable particles. This has novel phenomenological implications, which we discuss.
We explore a new class of simplified extensions to the Standard Model containing a complex singlet scalar as a dark matter candidate accompanied by a vector-like lepton as a mediator, both charged under a Z3 symmetry. In its simplest form, the new physics couples only to right-handed electrons, and the model is able to accommodate the correct dark matter relic abundance around the electroweak
scale up to several TeV evading the strongest constraints from perturbativity, collider and dark matter searches. Furthermore, the model is capable to enhance naturally positron fluxes by several orders of magnitude presenting box-shape spectra, and keeping sizable signals of gamma-rays. This framework gives rise to several phenomenological possibilities depending on the quantum charge assignments of the new fields.
In recent years a series of anomalies hinting at lepton flavor universality violation in B-meson decays have emerged. Interestingly, these anomalies can be coherently explained at the TeV scale by "4321" gauge models with hierarchical couplings reminiscent of the Standard Model (SM) Yukawas. This provides a tantalizing hint of new physics connected to the SM flavor puzzle at the same scale where the electroweak (EW) hierarchy problem is expected to be resolved. We show that 4321 models can arise as the low-energy limit of a complete theory of flavor, based on a warped fifth dimension where each Standard Model family is quasi-localized in a different brane. The SM Higgs is identified as a pseudo-Nambu-Goldstone boson emerging from the same dynamics responsible for breaking 4321 gauge symmetry. This novel construction unifies quarks and leptons in a flavor non-universal manner, provides a natural description of flavor hierarchies, and addresses the EW hierarchy problem a la Randall-Sundrum.
Experimental hints for lepton flavor universality violation in beauty-quark decay both in neutral- and charged-current transitions require an extension of the Standard Model for which scalar leptoquarks (LQs) are the prime candidates. Besides, these same LQs can resolve the long-standing tension in the muon and the recently reported deviation in the electron 𝑔−2 anomalies. These tantalizing flavor anomalies have discrepancies in the range of 2.5𝜎−4.2𝜎, indicating that the Standard Model of particle physics may finally be cracking. In this talk, we propose a resolution to all these anomalies within a unified framework that sheds light on the origin of neutrino mass. In this model, the LQs that address flavor anomalies run through the loops and generate neutrino mass at the two-loop order while satisfying all constraints from collider searches, including those from flavor physics.
In recent times, several hints of lepton flavour universality violation have been observed in semileptonic B decays, which point towards the existence of New Physics beyond the Standard Model. In this context, we consider a new variant of $U(1)_{L_{\mu}-L_{\tau}}$ gauge extension of Standard Model, containing three additional neutral fermions $N_{e}, N_{\mu}, N_{\tau}$, along with a $(\bar{3},1,1/3)$ scalar Leptoquark (SLQ) and an inert scalar doublet, to study the phenomenology of light dark matter, neutrino mass generation and flavour anomalies on a single platform. The lightest mass eigenstate of the $N_{\mu}, N_{\tau}$ neutral fermions plays the role of dark matter. The light gauge boson associated with $U(1)_{L_\mu-L_\tau}$ gauge group mediates dark to visible sector and helps to obtain the correct relic density. The spin-dependent WIMP-nucleon cross section is obtained in leptoquark portal and is looked up for consistency with CDMSlight bound. Further, we constrain the new model parameters by using the branching ratios of various $b \to sll$ and $b \to s \gamma$ decay processes as well as the lepton flavour non-universality observables $R_{K^{(*)}}$ and then show the implication on the branching ratios of some rare semileptonic $B \to (K^{(*)}, \phi)+$ missing energy, processes. The light neutrino mass in this model framework can be generated at one-loop level through radiative mechanism.
We investigate b→s flavor-anomaly solutions with U(1)' extensions in the framework of asymptotically safe quantum gravity. We study three different U(1)' extensions with vector-like fermions and a scalar field whose vev breaks the new U(1)'. The universal contribution of quantum gravity to renormalization group equations (RGEs) of all the gauge and the Yukawa couplings, beyond the Planck scale, ensues interdependent boundary conditions between the Standard Model and the New Physics (NP) couplings during the flow of RGEs from an interactive UV fixed point. As a result, precise measurements of low-energy SM couplings fix the exact values of the NP couplings, and accordingly, the NP mass range can be significantly narrowed down. We confront the models parameter space with the various LHC searches for VL fermions and the new gauge boson Z'. We find a viable parameter space with a potential to probe entirely in LHC Run 3.
In this talk, I will discuss vector-like fermion explanations for the recent anomalies in the precision measurements; muon g-2, semi-leptonic B meson decays, as well as W boson mass. These deviations from the SM predictions can be addressed in models with vector-like fermions together with a new U(1) gauge symmetry or scalar field dark matter. I shall then discuss LHC limits on the vector-like leptons which are predicted to be light to explain the anomalies. This talk is based on arXiv: 2205.10480, 2204.07022, 2104.04461 [PRD104(2021)3,035007],1911.11075 [PRD101(2020)3,035026] and 1906.11297 [PRD100(2019)5,055030].
In explaining the EWSB, it was postulated that Higgs boson might be a composite state of pNBGs from the breaking of a larger global group. The AdS/CFT correspondence provides a dual theory which is weakly coupled to perform the perturbative calculations, for example the particles spectrum. In applications to QCD-like theories, the AdS/QCD models are developed. In this talk I will introduce a non-Abelian AdS/QCD model and show the corresponding meson spectrum.
Gauge-Higgs Grand Unified Theories (GHGUT) embedded in a 5D spacetime unify the gauge symmetries of nature together with their breaking sector, at the same time providing a solution to the gauge hierarchy problem, the flavour puzzle, and the doublet-triplet splitting problem. In this talk, I will discuss the recently proposed 5D warped space GHGUT setup with an SU(6) bulk gauge group, where the 5D gauge field contains the conventional SU(5) GUT gauge bosons and a scalar sector, which includes the Higgs field, as the fifth component of 5D gauge bosons. With suitably chosen boundary conditions that break SU(6) down to the SM gauge group, all the SM fermion masses and mixings are reproduced with a minimal fermion content. Moreover, the problem of light exotic Kaluza-Klein fermions, which generically appear in GHGUTs, is avoided. The scalar sector comprises three fields, namely the SM Higgs, a leptoquark (LQ), and a singlet. The scalar potential is computed at one loop, leading to realistic Higgs masses mh ~ 125 GeV, and TeV-scale masses for the LQ and the singlet, potentially within reach of the LHC. I will also show that, although the coloured GUT gauge bosons (scalar LQ) have masses in the multi-TeV (TeV) range, proton decay is forbidden by a baryon number symmetry following from the SM fermion embeddings in SU(6). Finally, I will highlight some flavour constraints coming from flavour changing neutral current (FCNC) processes.
Gauge-Higgs Grand Unification Theories (GHGUTs) offer an interesting direction to solve some of the open questions of the SM, like the Hierarchy Problem and the Flavor Puzzle. Moreover, they allow for the unification of the gauge symmetries and their breaking sector. In this talk we discuss the evolution of coupling constants in GHGUTs, specifically a recently proposed minimal SU(6) warped GHGUT, with the goal of unification of the three SM couplings. Differences to ordinary 4D calculations are discussed and it is shown that the running of coupling constants is similar to the original Georgi-Glashow SU(5) model.
The Standard Model (SM) fermion mass generation in the (Partially) Composite Higgs framework may suffer from problems due to, for example, reintroduction of new SM naturalness problems, generation of dangerous flavor changing neutral currents, instability of the Higgs vacuum, or challenging non-minimal model building. All these problems can be alleviated if these models have a large compositeness scale, but this requires an unnatural small vacuum misalignment. Therefore, I propose UV complete (Partially) Composite Higgs models with compositeness scale up to the Planck scale assisted by a novel mechanism. This mechanism is based on softly breaking a global Z2 symmetry by technically natural small vacuum misalignment, dynamically triggering the electroweak symmetry breaking and SM fermion mass generation. I consider a concrete model example that fulfills this, where all the dimensionful fundamental parameters are approximately in the order of 10^18 GeV. In addition, this concrete model example may also predict measurable gravitational waves, the neutrino masses, and the inflation.
Simple scalar extensions of the Standard Model (SM) with a spontaneously broken $Z_2$ symmetry allow for a strongly first order electroweak phase transition, as sought in order to realize electroweak baryogenesis. To avoid the emergence of phenomenologically problematic domain walls one may encounter in this context, in 2112.12087 (A. Angelescu, F. Goertz, AT), a scalar singlet framework featuring a thermal history which does not restore $Z_2$ in the early universe is proposed. This can be realized by introducing D>4 operators in an effective field theory (EFT). A possible UV completion is provided by $SO(6)/SO(5)$ composite Higgs models, where the scalar potential and Yukawa interactions are obtained in spurion analyses and spontaneously CP-violating terms arise. The model with SM fermions in a symmetric $20^\prime$ of $SO(6)$ is successfully matched to the envisaged EFT parameter space. The scenario can then fulfill all Sakharov criteria while accounting for the electroweak hierarchy problem.
Antisymmetric tensor field (two-form field) is a ubiquitous component in string theory and generally couples to the scalar sector through its kinetic term. In this paper, we propose a cosmological scenario that the particle production of two-form field, which is triggered by the background motion of the coupled inflaton field, occurs at the intermediate stage of inflation and generates the sizable amount of primordial black holes as dark matter after inflation. We also compute the secondary gravitational waves sourced by the curvature perturbation and show that the resultant power spectra are testable with the future space- based laser interferometers.
In this talk, I will give a brief introduction to quintessential inflation, a theoretical framework that aims to explain both inflation and dark energy observations to alleviate the incredible fine-tuning of ΛCDM. Furthermore, I will show how adding both an R^2 Starobinsky term and a non-minimal coupling to the inflaton/quintessence field term in the action in the Palatini formalism can rescue the exponential potential, which is well known not to be valid for either inflation or dark energy in the canonical setup. Since the full equations of motion in the Jordan frame are numerically solved, and a parameter scan of the theory is performed, we are able to obtain specific testable predictions, such as the barotropic parameter of dark energy and its running, which will be testable in the near future, as well as constraints on the theory, e.g., on the value of the running of the non-minimal coupling term.
It is becoming increasingly clear that large but rare fluctuations of the primordial curvature field, controlled by the tail of its probability distribution, could have dramatic effects on the current structure of the universe — e.g. via primordial black-holes. However, the use of standard perturbation theory to study the evolution of fluctuations during inflation fails in providing a reliable description of how non-linear interactions induce non-Gaussian tails. In this work, we use the stochastic inflation formalism to study the non- perturbative effects from multi-field fluctuations on the statistical properties of the primor- dial curvature field. Starting from the effective action describing multi-field fluctuations, we compute the joint probability density function and show that enhanced non-Gaussian tails are a generic feature of slow-roll inflation with additional degrees of freedom.
Hidden U(1) symmetries in the right-handed neutrino ($\nu_R$) sector are theoretically well-motivated and would give rise to an inherently dark gauge boson which we refer to as the $\nu_R$-philic $Z'$. An important feature of this $Z'$ is that its couplings to neutrinos are generally much larger than its couplings to charged leptons and quarks, providing a particularly interesting scenario for future neutrino experiments such as DUNE to probe. In this talk, I'll discuss two approaches to probe this $Z'$ at DUNE near detectors via (i) searching for $Z'$ decay signals and (ii) precision measurement of elastic neutrino-electron ($\nu$-$e$) scattering. I will show that the former will have sensitivity comparable to or better than previous beam dump experiments while the latter will improve current limits substantially for large neutrino couplings.
Neutrino oscillations in matter offer a novel path to investigate new physics. The most recent data from the two long-baseline accelerator experiments, NO$\nu$A and T2K, show discrepancy in the standard 3-flavor scenario. Along the same line of discussion, we intend to explore the next generation of long-baseline experiments: T2HK and DUNE. We investigate the sensitivities of relevant NSI couplings ($|\epsilon_{e \mu}|$, $|\epsilon_{e \tau}|$) and the corresponding CP-phases ($\phi_{e \mu}$ and $\phi_{e \tau}$). While both the experiments are sensitive to non-standard interactions (NSI) of the flavor changing type arising from $e-\mu$ and $e-\tau$ sectors, we show that DUNE is more sensitive to these NSI parameters when compared to that of T2HK. At the same time, we aim to explore the impact of non-standard neutrino interaction on the sensitivity of standard CP-phase $\delta_{CP}$ and atmospheric mixing angle $\theta_{23}$ in the normal as well as inverted hierarchies. Our analysis also exhibits the difference in probabilities for both the experiments with inclusion of NSI.
The latest data of the two long-baseline accelerator experiments NOνA and T2K, interpreted in the standard 3-flavor scenario, display a discrepancy. A mismatch in the determination of the standard CP-phase $\delta_{\rm CP}$ extracted by the two experiments is evident in the normal neutrino mass ordering. While NOνA prefers values close to $\delta_{\rm CP} ∼ 0.8\pi$, T2K identifies values of $\delta_{\rm CP} ∼ 1.4\pi$. Such two estimates are in disagreement at more than 90% C.L. for 2 degrees of freedom. We show that such a tension can be resolved if one hypothesizes the existence of complex neutral-current non-standard interactions (NSI) of the flavor changing type involving the $e-\mu$ or the $e-\tau$ sectors with couplings $|\varepsilon_{e\mu}|$ ∼ $|\varepsilon_{e\tau}|$ ∼ 0.2. Remarkably, in the presence of such NSI, both experiments point towards the same common value of the standard CP-phase $\delta_{\rm CP} ∼ 3\pi/2$. Our analysis also highlights an intriguing preference for maximal CP-violation in the non-standard sector with the NSI CP-phases having best fit close to $\phi_{e\mu} ∼ \phi_{e\tau} ∼ 3\pi/2$, hence pointing towards imaginary NSI couplings.
The upcoming campaign of cosmogenic neutrino measurements provides us not only a way to understand the cosmic ray accelerators but also a promising portal to study fundamental particle physics. The future observation of cosmogenic neutrinos is guaranteed given the unprecedented sensitivity of many experimental programs. In this talk, I summarize the new physics potential of those facilities, with an emphasis on tau neutrino telescopes. I first discuss the minimal particle physics models which can modify the neutrino-matter interactions directly. Then I move on to a powerful event topology, the double and multiple bangs, and discuss its potential in particle physics studies, particularly for sphalerons. In the end, I mention other interesting new physics possibilities, to which the cosmogenic neutrino measurements can be sensitive.
The leading order hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon is calculated by using lattice QCD. Compared to the result of the dispersive approach for this contribution, our finding significantly reduces the tension between the standard model prediction for the muon's magnetic moment and its measurement.
We discuss the prospects of probing the $L_\mu - L_\tau$ gauge boson at the MUonE experiment. The $L_\mu - L_\tau$ gauge boson $Z^\prime$ with a mass of $< 200$ MeV, which can explain the discrepancy between the measured value of the muon $g-2$ and the value calculated in the Standard Model, can be produced at the MUonE experiment through the process $\mu e \to \mu e Z^\prime$. The $Z^\prime$ in the final state decays into a pair of neutrinos, and therefore we cannot observe the decay of $Z^\prime$ directly. It is, however, still possible to probe this signature by searching for events with a large scattering angle of muon and a less energetic final-state electron. The background events coming from the elastic scattering $\mu e \to \mu e$ as well as radiative process $\mu e \to \mu e \gamma$ can be removed by the kinematical cuts on the muon scattering angle and the electron energy, in addition to a photon veto. The background events from the electroweak process $\mu e \to \mu e \nu \bar{\nu}$ are negligible. With our selection criteria, the number of signal events $\mu e \to \mu e Z^\prime$ is found to be as large as $\sim 10^3$, assuming an integrated luminosity of $15~\mathrm{fb}^{-1}$, in the parameter region motivated by the muon $g-2$ discrepancy. It is, therefore, quite feasible to probe the $L_\mu - L_\tau$ gauge boson at the MUonE experiment---without introducing additional devices---and we strongly recommend recording the events relevant to this $Z^\prime$ production process.
U(1)Lµ−Lτ ≡ U(1)X model is anomaly free within the Standard Model (SM) fermion content, and can accommodate the muon (g−2) data for MZ′ ∼ O(10−100) MeV and gX ∼ (4−8)×10−4. WIMP type thermal dark matter (DM) can be also introduced for MZ′ ∼ 2MDM, if DM pair annihilations into the SM particles occur only through the s-channel Z′ exchange. In this work, we show that this tight correlation between MZ′ and MDM can be completely evaded both for scalar and fermionic DM, if we include the contributions from dark Higgs boson (H1). Dark Higgs boson plays a crucial role in DM phenomenology, not only for generation of dark photon mass, but also opening new channels for DM pair annihilations into the final states involving dark Higgs boson, such as dark Higgs pair as well as Z′Z′ through dark Higgs exchange in the s-channel, and co-annihilation into Z′H1 in case of inelastic DM. Thus dark Higgs boson will dissect the strong correlation MZ′ ∼ 2MDM, and much wider mass range is allowed for U(1)X-charged complex scalar and Dirac fermion DM, still explaining the muon (g − 2). We consider both generic U(1)X breaking as well as U(1)X → Z2 (and also into Z3 only for scalar DM case).
Given current discrepancy in muon $g-2$ and future dedicated efforts to measure muon electric dipole moment (EDM) $d_\mu$, we assess the indirect constraints imposed on $d_\mu$ by the EDM measurements performed with heavy atoms and molecules. We notice that the dominant muon EDM effect arises via the muon-loop induced “light-by-light” CP-odd amplitude $\propto E^3B$, and in the vicinity of a large nucleus the corresponding parameter of expansion can be significant, $eE_\mathrm{nucl}/m_\mu^2∼0.04$. We compute the $d_\mu$-induced Schiff moment of the $^{199}$Hg nucleus, and the linear combination of $d_e$ and semileptonic $C_S$ operator (dominant in this case) that determine the CP-odd effects in the ThO molecule. The results, $d_\mu ({}^{199}\mathrm{Hg})<6\times 10^{-20}e\,\mathrm{cm}$ and $d_\mu (\mathrm{ThO})<2\times 10^{-20}e\,\mathrm{cm}$, constitute approximately threefold and ninefold improvements over the limits on $d_\mu$ extracted from the Brookhaven National Laboratory muon beam experiment.
Experiments using proton beams at high luminosity colliders and fixed-target facilities provide impressive sensitivity to new light weakly coupled degrees of freedom. We revisit the production of dark vectors and scalars via proton bremsstrahlung for a range of beam energies, including those relevant for the proposed Forward Physics Facility (FPF) at the High Luminosity LHC. In addition, we extend the application of proton bremsstrahlung to other long-lived dark sectors such as axion-like particles (ALPs) with gluon coupling and millicharged particles. In another direction, we utilize the significant neutrino flux in the forward direction at the LHC to study the electromagnetic properties of neutrinos, which serve as a probe to new physics beyond the Standard Model. In particular, we set stringent constraints on the magnetic moment, millicharge, and charge radius of tau neutrinos.
We consider a simple extension of the Standard Model with a vector-like lepton and U(1)’ gauge symmetry motivated by the recent experimental anomalies in the muon g-2 and the W boson mass. After the U(1)’ symmetry is spontaneously broken, the mixings between the muon and the vector-like lepton and between the Z boson and the U(1)’ gauge boson arise. As a result, we obtain the desirable corrections to the muon g-2 and the W boson mass. For the muon g-2 contribution, a natural choice for the bare mass of the muon leads the robustness with respect to the vector-lepton mass thanks to the seesaw mechanism for the lepton masses. We extend our U(1)’ gauge symmetry model to an SU(2) dark gauge symmetry model that accommodates a vector dark matter candidate.
The existence of a mass gap between Standard Model and possible New Physics states has been confirmed experimentally. As a consequence, effective field theories are appropriate to search for signals beyond the Standard Model. We consider a non-linear realization of the electroweak symmetry breaking, where the Higgs is a singlet with independent couplings and the Standard Model fields are coupled to bosonic heavy resonances. We present a preliminary next-to-leading-order calculation of the oblique $S$ and $T$ parameters. The experimentally allowed range of the $S$ and $T$ parameters constrain the resonances to be heavy enough, with masses above the TeV scale, $M_R > 2\,$TeV, in good agreement with our previous estimations, where only P-even operators were considered.
After developing a general criterion for deciding which neutrino mass models belong to the category of inverse seesaw models, we apply it to obtain the Dirac analogue of the canonical Majorana inverse seesaw model. We then generalize the inverse seesaw model and obtain a class of inverse seesaw mechanisms both for Majorana and Dirac neutrinos. We further show that many of the models have double or multiple suppressions coming from tiny symmetry breaking “μ-parameters”. These models can be tested both in colliders and with the observation of lepton flavour violating processes.
Many popular extensions of the SM require sizeable modifications to the trilinear Higgs boson coupling in order to accommodate a first-order electroweak (EW) phase transition. Cosmological first-order phase transitions can give rise to a primordial gravitational wave (GW) background which could be observable at future space-based GW detectors such as LISA. Focusing on the Yukawa type-II 2HDM and taking into account various theoretical and experimental constraints in combination with the condition of the presence of a first-order EW phase transition, we scrutinize the relevant parameter space regions and verify whether these regions could be probed in a complementary way at the HL-LHC via nonresonant Higgs boson pair production and at the LISA experiment via the possible observation of a GW signal. We find regions of the parameter space that give rise to GW signals that might be detectable at LISA, and these regions predict values of the triple Higgs boson couplings that are potentially observable at the HL-LHC or other future colliders. The measurements of Higgs boson pair production will therefore provide important constraints on the possiblity of observing GW signals at LISA.
According to the standard model of cosmology, the Universe at its very beginning underwent a phase of rapid expansion, followed by a reheating period. During this epoch, the energy density, initially accumulated in the oscillations of the inflaton field, was injected into the visible sector, eventually setting the initial conditions for the hot big bang. In this talk, I will discuss the perturbative production of the Standard Model (SM) and dark matter (DM) particles during the reheating phase, assuming a non-standard expansion history. In particular, I will explore a scenario in which reheating is induced by a cubic interaction of the inflaton $\phi$ with the SM Higgs doublet $\bf{h}$ of the form $g_{h \phi} M_{\rm Pl} \phi |\mathbf{h}|^2$. In the presence of such interaction, the Higgs field acquires a $\phi$-dependent mass which generates a vacuum expectation value that oscillates in time and breaks the SM gauge symmetry. Furthermore, the non-zero mass of the Higgs field leads to a time-dependent inflaton decay rate and generates a non-trivial phase-space suppression of the SM radiation production. As a consequence, the reheating phase is prolonged, and the maximal temperature of the SM thermal bath is reduced. This, in turn, has non-trivial consequences for the dark sector, especially for the UV freeze-in DM scenario.
We discuss the energy distribution and equation of state of the universe between the end of inflation and the onset of radiation domination for observationally consistent single-field inflation scenarios, with a potential ’flattening’ at large field values and a monomial shape around the origin. As a proxy for (p)reheating, the inflaton is coupled to a light scalar field with a quadratic interaction and we investigate the non-perturbative and non-linear dynamics of this system with the help of lattice simulations. For particular cases we are able to calculate the exact number of e-folds until radiation domination, which significantly reduces the uncertainty in the inflationary observables, the spectral tilt and tensor-to-scalar ratio.
The mixed Higgs-R^2 inflation model is a two-field inflation model with minimal setup within general relativity (GR) and Standard Model (SM), which is a promising UV extension of the Higgs inflation model with a cutoff scale up to Planck scale. The model can be described as an effective Starobinsky model during inflation with effectively a single parameter while the reheating phenomena are rich due to the multi-field nature, including "spike preheating", tachyonic preheating, and perturbative reheating which occur for different parameter choices and dominate different stages of reheating. Thorough investigation of reheating in this model enables us to improve the observational constraints from CMB on the model parameter.
In inflationary cosmology, the Universe must transition from a state dominated by the nearly homogeneous inflaton condensate, into a state dominated by a hot bath of Standard Model particles, a process known as reheating. Detailed modelling of this transition often reveals the presence of exponentially growing instabilities, whose dynamics is typically referred to as preheating. A common example occurs when the inflaton undergoes oscillations around a potential minimum shortly after the inflationary phase ends. Linear fluctuations of either the inflaton or fields coupled to it then obey a wave equation with an oscillating mass, leading to exponential growth of certain bands of wavenumbers. Eventually these growing modes become large enough to undergo strong mode-mode coupling, leading to a fracturing of the inflaton and a breakdown of the assumption of homogeneity. Depending on the specific model, the resulting complex medium can display a range of interesting properties, including: the emergence of scaling regimes dominated by log-normal density fluctuation, the production of topological defects, and the creation of long-lived approximate solitary waves. This nonlinear stage can only be studied using semiclassical lattice simulations. While these lattice simulations are believed to provide a good approximation to the full quantum dynamics, they have never been tested with experiments leaving the possibility for novel quantum phenomena.
I will show how we can emulate end-of-inflation dynamics in the lab using two coupled dilute gas Bose-Einstein condensates (BECs), providing the exciting opportunity to experimentally study the end-of-inflation. First, I will explain the connection between the (nonrelativistic) BEC dynamics and relativistic scalar field relevant to cosmology. In particular, by appropriately tuning parameters, the evolution of the relative phase of the BECs is well described by the relativistic sine-Gordon model. To study preheating, we begin with two nearly homogeneous BECs and imprint an initial relative phase between them. The relative phase then undergoes oscillations analogous to a rigid pendulum. Of course, quantum mechanics ensures that the condensates cannot be perfectly homogeneous, and small quantum fluctuations must be present initially. In the sine-Gordon theory, there is a single band of linearly unstable modes which grow exponentially in the presence of a homogeneous oscillating background. As a first step, I will demonstrate that the cold atom system replicates the linear instability of the sine-Gordon model. I will also quantify the deviations from the pure sine-Gordon limit, showing they are small. I then use lattice simulations of the BECs to study the full nonlinear evolution of the condensates. I will show that once the fluctuations enter the nonlinear regime, the relative phase fractures into a collection of localized oscillating field configurations, known as oscillons. This behaviour matches that seen in simulations of the pure sine-Gordon model.
Time permitting, I will briefly comment on possible applications to the emergence of domain wall networks and to relaxion dynamics. The former occurs when we start the condensates $\pi$ out of phase with each other, while the latter occurs when we allow the relative phase to undergo full rotations thus scanning many minima of the effective sinusoidal potential. More generally, since the effective relativistic field is a phase variable, these BEC systems may be useful to experimentally study a broad class of axions relevant to cosmology.
Cosmological relaxation of the electroweak scale provides an elegant solution to the Higgs mass hierarchy problem. In the simplest model, the Higgs mass is scanned during inflation by another scalar field, the relaxion, whose slow-roll dynamics selects a naturally small Higgs vev. In this work we investigate the mechanism in a less conventional regime where the relaxion is subject to large fluctuations during its dynamics. We identify modified stopping conditions for such dynamics of the relaxion and find the new parameter space. In a large region of the parameter space, the relaxion can naturally explain the observed dark matter density in the universe.
In this talk, I will discuss elastic scattering processes between nucleons and the QCD axion dark matter. I point out that the cross section can be enhanced by more than $\mathcal{O}(10^{25})$ by the coherent effect, compared to classical processes.In addition, one may expect stimulated emission effects can also enhance the cross section because the number density of the axion DM is very large. The enhancement factor can be as large as another $\mathcal{O}(10^{25})$ and, if the factor exists, the force from the dark matter wind may be detected via e.g., torsion balance experiments. However, it is also found that there is a cancellation of the stimulated emission factor and the force is too small to be detected.
Belle has unique reach for a broad class of models that postulate the existence of dark matter particles with MeV—GeV masses. This talk presents recent world-leading physics results from Belle II searches for dark Higgstrahlung and invisible Z′ decays; as well as the near-term prospects for other dark-sector searches.
The DMRadio suite of experiments seeks to search for one of the most promising Dark Matter (DM) candidates, the axion, via an optimized resonant lumped element search. In order to cover as wide of a parameter space as possible, each of the DMRadio experiments is designed to cover specific complementary mass regions starting from 5 kHz ($\approx$ 20 peV) in the DMRadio-50L experimental all the way up to 200 MHz ($\approx$ 1 $\mu$eV) with the DMRadio-m$^3$ experiment. At the same time, the DMRadio-50L experiment will serve as a testbed for accelerated axion searches with quantum sensors. In this talk, we will present an overview of the DMRadio program, discuss the optimization campaign together with the current construction efforts on the DMRadio-50L experiment, discuss the future goals for the DMRadio-m$^3$ experiment, as well as the development of a future search for GUT-scale QCD axions in the MHz region.
Although very constrained in the matter sector, violations of Lorentz invariance are still allowed in gravitational systems, provided that they are sufficiently suppressed. Actually, some models of Lorentz violating gravity, such as Horava gravity, provide interesting ways of UV completing gravitation. Beyond that, they can also have implications for macroscopic physics and astrophysical models. In this talk I will discuss the current status of Horava gravity (and its low energy version, related to Einstein-Aether gravity) in connection to black hole physics and other compact objects. In particular, I will review the issue of constructing BHs in these theories, as well as the problem of bounding deviations from GR by using binary pulsar measures and gravitational wave observations.
We show that primordial black holes (PBHs) develop non-negligible spins through Hawking emission of the large number of axion-like particles generically present in string theory compactifications. This is because scalars can be emitted in the monopole mode (l=0), where no angular momentum is removed from the BH, so a sufficiently large number of scalars can compensate for the spin-down produced by fermion, gauge boson, and graviton emission. The resulting characteristic spin distributions for $10^8-10^{12}$ kg PBHs could potentially be measured by future gamma-ray observatories, provided that the PBH abundance is not too small. This yields a unique probe of the total number of light scalars in the fundamental theory, independent of how weakly they interact with known matter. The present local energy density of hot, MeV-TeV, axions produced by this Hawking emission can possibly exceed $ρ_{CMB}$. Evaporation constraints on PBHs are also somewhat weakened.
Primordial Black Holes (PBHs) are black holes that could have been formed in the very early universe due to the collapse of large curvature fluctuations after inflation. PBHs are nowadays one of the most attractive and fascinating research areas in cosmology for their possible theoretical and observational implications. In this talk, I will review the physical process of PBH formation and give some new results regarding the numerical formation of PBHs during the QCD phase transition. In this scenario, the temporal reduction that suffers the equation of state can modify the threshold of PBH formation in such a way to produce BHs with masses order solar mass, which could be detected with current gravitational wave detectors.
Scattering amplitudes mediated by graviton exchange display IR singularities in the forward limit. This obstructs standard application of positivity bounds based on twice subtracted dispersion relations. Such divergences can be cancelled only if the UV limit of the scattering amplitude behaves in a specific way, which implies a very non-trivial connection between the UV and IR behaviors of the amplitude. We show that this relation can be expressed in terms of an integral transform, obtaining analytic results when t log s → 0. Carefully applying this limit to dispersion relations, we find that infinite arc integrals, which are usually taken to vanish, can give a non-trivial contribution in the presence of gravity, unlike in the case of finite negative t. This implies that gravitational positivity bounds cannot be trusted unless the size of this contribution is estimated in some way, which implies assumptions on the UV completion of gravitational interactions. We discuss the relevance of these findings in the particular case of QED coupled to gravity.
We present a comprehensive non-perturbative study of the phase structure of the asymptotically safe Standard Model. The physics scales included range from the asymptotically safe trans-Planckian regime in the ultraviolet, the intermediate high energy regime with electroweak symmetry breaking to strongly correlated QCD in the infrared. All flows are computed with a self-consistent functional renormalisation group approach, using a vertex expansion in the fluctuation fields. In particular, this approach takes care of all physical threshold effects and the respective decoupling of ultraviolet degrees of freedom. Standard Model and gravity couplings and masses are fixed by their experimental low energy values. Importantly, we also accommodate for the difference between the top pole mass and its Euclidean analogue. Both, the correct mass determination and the threshold effects have a significant impact on the qualitative properties, i.e. the number of relevant directions, of the ultraviolet fixed point as well as the stability properties of the specific ultraviolet-infrared trajectory with experimental Standard Model physics in the infrared. We show, that in the present rather advanced approximation the matter part of the asymptotically safe Standard Model has the same number of relevant parameters as the Standard Model, and is asymptotically free. Interestingly, the fixed-point Higgs potential is flat but has two relevant directions. These results and their analysis are based and accompanied on a thorough discussion of the systematic error of the present truncation, also important for systematic improvements.
Effective field theories of QCD, such as soft collinear effective theory with Glauber gluons, have led to important advances in understanding of many-body nuclear effects. We provide first applications to QED processes. We study the exchange of photons between charged particles and the nuclear medium for (anti)neutrino-, electron-, and muon-induced reactions inside a large nucleus. We provide analytical expressions for the distortion of (anti)neutrino-nucleus and charged lepton-nucleus cross sections and estimate the QED-medium effects on the example of elastic lepton-nucleon reactions in kinematics of modern and future experiments. We find new permille-level effects, which were never accounted for in either (anti)neutrino-nucleus or electron-nucleus scattering.
We introduce a new approach to renormalize physical quantities in curved space-time
by adiabatic subtraction. We use a comoving infrared cut-off in defining the adiabatic counterpart of
the physical quantity under consideration. We show how this infrared cut-off should be used to
obtain a completely well-defined renormalization scheme and how it is fundamental to avoid unphysical
divergences that can be generated by a pathological behavior of the adiabatic subtraction extended
to the infrared domain. The infrared cut-off appears as a new degree of freedom introduced in the theory
and its actual value has to be consistently fixed by a physical prescription. As an example, we show
how such degree of freedom can be set to obtain the correct value of the conformal anomaly in the
symptomatic case of an inflationary model with gauge fields coupled to a pseudo-scalar inflaton.
One of the most basic open questions in cosmology is if dark energy is associated just with a cosmological constant or with something more involved. In this contribution, we emphasize that dark energy can be taken as constant under very general assumptions. Following this line of reasoning, we define the vacuum frame and discuss cosmological evolution from this new point of view.
We introduce the Cascading Dark Energy (CDE) scenario, in which one or some of the fields that contribute cooperatively to the recent cosmic acceleration, leave the band (cascade) and start acting on their own by oscillating around their minima. This process, in particular, could happen due to the different initial conditions of the field(s). Due to this dropout and energy injection, the Hubble parameter today increases in comparison with what is expected from the vanilla single field dark energy and ${\rm \Lambda}$CDM. We illustrate the idea through an $N+1$-field model that effectively reduces to a two-field model of CDE. In this work, we assume that the potentials of both fields take the quartic monomial form. We use the publicly available code CosmoMC to constrain our model in the light of the observational data from different sources.} We exactly and numerically solve for the equations of motion for the fields without resorting to the fluid approximations used in the literature. We show that our model fits the data better than the $\Lambda$CDM model, and also the single-field scenario with a quartic potential. Our model gives today's Hubble parameter as $H_0=70.95^{+0.62}_{-0.85}$ km/s/Mpc at $1\sigma$, which is more consistent with the Riess 2019 measurement $H_0=73.03\pm1.42$ km/s/Mpc, in comparison with the predictions of the $\Lambda$CDM and single-field dark energy models, which are ($H_0=68.60\pm 0.41$ km/s/Mpc). $\Delta \chi_{tot}^2$ gets reduced relative to $\Lambda$CDM and single-field dark energy, respectively by $6.51$ and $5.8$. We conclude that our model can ameliorate the $H_0$ existing tensions among the cosmological data from different sources.
Tunnelling between degenerate vacuua is allowed in finite-volume Quantum Field Theory, and features remarkable energetic properties, which result from the competition of different dominant configurations in the partition function. During my talk, I will be presenting the results of our recent paper, arXiv:2203.12543, where we derive the one-loop effective potential based on two homogeneous vacuua of the bare theory, and discuss the resulting Null Energy Condition violation in O(4)-symmetric Euclidean spacetime, as a result of a non-extensive effective action.
These results have interesting implications as a possible contribution to dark energy or as a dynamical mechanism for generating a cosmological bounce. I will also discuss some preliminary results for extending these results to finite-temperature field theory.
The mechanism that produces the dark energy driving the expansion of the universe remains a mystery. One popular proposal is to have a scalar field play the role of dark energy. Such a field would have, at least, indirect coupling to matter and so result in a new fundamental force which could be used as a probe to detect these fields. However, no such 'fifth force' has been detected so far, placing strong constraints on models of this type. The 'chameleon' is a scalar field that couples to matter but due to its nonlinear effective potential it possesses a screening mechanism which allows it to evade detection in high density regions such as our solar system, while still having a measurable effect on cosmological scales. The difficulty of this and similar models is that the nonlinear equations lack known analytic solutions except in highly symmetric cases. To this end we have developed a Python package named SELCIE (Screening Equations Linearly Constructed and Iteratively Evaluated) which allows the user to construct systems with arbitrary density profiles and solve for the resulting chameleon field profile. It accomplishes this by using the gmsh and FEniCS software packages. This software has already been used to investigate which properties of NFW halos maximise the likelihood of detecting fifth forces generated by the chameleon field. Using this tool the chameleon field profile for complex systems can be determined, allowing for new probes both from astrophysical observations and laboratory experiments.
A sterile neutrino with a keV-scale mass is a compelling dark matter candidate. We propose a new production mechanism involving the decay and annihilation of a complex scalar singlet with a Higgs portal coupling which develops a vacuum expectation value. The interactions of the resulting pseudo Nambu-Goldstone boson may thermalise the dark sector. We determine the region of parameter space where dark sector thermalisation is reached and discuss the most relevant cosmological observables. The scenario can be considered as the combination of a freeze-in of the dark sector followed by relativistic freeze-out.
The talk is based on 2204.08795 [hep-ph]
I will illustrate the complementary constraints in a 2HDM model, augmented with a U(1) symmetry, featuring right-handed neutrino Dark Matter and considering different production mechanims both in standard and non standard cosmological scenarios.
Sterile neutrinos with keV-scale masses are popular candidates for warm dark matter. In the most straightforward case, they are produced via oscillations with active neutrinos. Our focus is on mixing with electron neutrinos, which is subject to constraints from several upcoming or running experiments like TRISTAN, ECHo, and HUNTER. We introduce effective self-interactions of active neutrinos and investigate the effect on the parameter space of sterile neutrino mass and mixing. We demonstrate that depending on the size of the self-interaction, the parameter space moves closer to, or further away from, the one testable by those future experiments. In particular, we show that phase 3 of the HUNTER experiment would test a larger amount of parameter space in the presence of self-interactions than without them. We also investigate the effect of the self-interactions on the free-streaming length of the sterile neutrino dark matter, which is important for structure formation observables.
We propose a new production mechanism for keV sterile neutrino dark matter which does not rely on the oscillations between sterile and active neutrinos nor on the decay of additional heavier particles, and works without employing any new interactions for the sterile neutrinos beyond the standard Yukawa couplings. The dark matter neutrinos are instead produced out of thermal freeze-out, much like typical a WIMP. The challenge consists in balancing a large Yukawa coupling so that the sterile neutrinos thermalize in the early universe on the one hand, and a small enough Yukawa coupling such that they are stable on cosmological scales on the other. We solve this problem by implementing varying Yukawa couplings. We achieve this by using a three-sterile neutrino seesaw extension to the SM and embedding it in a Froggatt-Nielsen model with one single flavon. If the vev of the flavon changes during the electroweak phase transition, the effective Yukawa couplings of the fermions have different values before and after the phase transition, thus allowing for successful dark matter genesis. Additionally, the flavour structure and the origin of the light neutrino masses are explained by the interplay of the seesaw and Froggatt-Nielsen mechanisms.
Standard Model extensions with a light stable axion are well-motivated by the observed Dark Matter abundance and the Peccei-Quinn solution to the Strong CP Problem. In general axions can have large flavor-violating couplings to SM fermions, which naturally arise in scenarios where the Peccei-Quinn symmetry also explains the hierarchical pattern of fermion masses and mixings. I will discuss how these couplings allow for efficient axion production from the decays of SM particles, giving the opportunity to probe flavored axion Dark Matter with precision flavor experiments, astrophysics and cosmology.
Inspired by the S.M.A.S.H framework we construct a model that adresses the strong CP problem, axion dark matter, inflation and Dirac neutrino masses as well as Leptogenesis. The model possesses only two dynamical scales, namely the SM breaking scale $v_H$ and the PQ breaking scale $v_\sigma$.
We introduce heavy vector-like quarks in the usual KSVZ fashion to implement the Peccei Quinn (PQ) mechanism for the strong CP problem. To generate neutrino masses via a dimension six operator scaling as $m_\nu \sim v_H^3 / v_\sigma^2$ we add heavy triplet and doublet leptons, which are vector-like under the SM but chiral under PQ symmetry. The model is free from the cosmological domain wall problem and predicts an axion to photon coupling which is about an order of magnitude larger than in conventional DFSZ and KSVZ models. Thus our scenario can be probed and potentially excluded by current and next generation axion experiments such as ORGAN or MADMAX.
In addition we numerically demonstrate that our construction can generate the observed baryon asymmetry by realizing a version of the Dirac-Leptogenesis scenario. As a consequence of our neutrino mass mechanism we find that the asymmetry in triplet fermion decays can also be significantly enhanced by up to six orders of magnitude when compared to typical Seesaw scenarios without needing to invoke a resonant enhancement. In passing we note that a decaying Dirac fermion with multiple decay modes contains all the necessary ingredients required for the “quasi optimal efficiency”-scenario previously encountered in the context decaying scalar triplets. The impact of the active right handed neutrinos and the axion on the amount of dark radiation $\Delta N_\text{eff}$ is estimated, which lies within current bounds and can also be diluted via entropy generation from the decay of a potentially long lived scalar responsible for the spontaneous breaking of PQ symmetry.
Axion is one of the promising candidates for light dark matter (DM). Although the mass scale of axion is multifarious, the keV scale would be interesting. Because an excess has been reported in the XENON1T experiment and such a direct search experiment can probe the axion with a mass of keV scale. The crucial constraint for axion in this mass range is the X-ray bound. Due to this, for the usual axion, its decay constant should be GUT scale or more and this follows that the corresponding axion-electron coupling is far away from the sensitivity of the direct search experiments. On the other hand, anomaly-free axion can evade the severe X-ray bounds and at the same time, can simultaneously explain DM and the XENON1T excess at the intermediate scale of the decay constant. In this talk, we consider a three Higgs doublet model (3HDM) as a possible renormalizable model where the anomaly-free axion can be embedded. We discuss the effect of the mixing among the axion and CP-odd Higgs bosons predicted in 3HDM for the axion couplings. In addition, we clarify the relation between the axion and heavy Higgs bosons.
The apparently simple and elegant QCD axion solution to the Strong CP problem is well known to be affected by the so called “quality problem”, whose root lies in the smallness of the QCD-induced axion potential with respect to UV-suppressed operators explicitly breaking the anomalous PQ symmetry. In this talk we present a model which addresses this issue by postulating that the dominant contribution to the axion potential arises from an additional $USp(N-3)$ confining group, which at high scales unifies with Color into a Grand Color group. This setup robustly solves the Strong CP problem and features an axion parametrically heavier than the standard one, providing a visible axion around the GeV scale in the region of parameter space where the quality problem is sizeably ameliorated.
The Peccei-Quinn solution to the strong CP problem has a problematic aspect: it relies on a global U(1) symmetry which, although broken at low energy by the QCD anomaly, must be an extremely good symmetry of high-energy physics. This issue is known as the Peccei-Quinn quality problem. We propose a model where the Peccei-Quinn symmetry arises accidentally and is respected up to high-dimensional Planck-suppressed operators. The model is a SU(N) dark gauge theory with fermions in the fundamental and a scalar in the symmetric. The axion arises from the spontaneous symmetry breaking of the gauge group and the quality problem is successfully solved for large enough number of dark colors N. The model includes additional accidentally stable bound states which provide extra Dark Matter candidates beyond the axion.
The origins of the light neutrino masses, and the baryon asymmetry of the Universe remain some of the biggest open questions of particle physics. By extending the standard model with Majorana neutrinos, the light neutrino masses can be generated through the type-I seesaw mechanism, and the baryon asymmetry of the Universe through leptogenesis. We study low-scale leptogenesis with Majorana neutrino masses between the MeV and TeV scales, covering the entire experimentally accessible mass range. I will talk about the two realizations of this mechanism - leptogenesis via neutrino oscillations and resonant leptogenesis, and demonstrate that their parameter space is united. We find that leptogenesis is viable in a wide range of parameters, including active-sterile mixing angles large enough to be testable at planned intensity experiments or future colliders (in the minimal scenario with two sterile neutrinos), or even exceeding the existing experimental bounds (in the scenario with three sterile neutrinos).
The Type II Seesaw Mechanism provides a minimal framework to explain the neutrino masses involving the introduction of a single triplet Higgs to the Standard Model. However, this simple extension was believed to be unable to successfully explain the observed baryon asymmetry of the universe through Leptogenesis. In our previous work (Phys. Rev. Lett. 128, 141801), we demonstrated that the triplet Higgs of the Type II Seesaw Mechanism alone can simultaneously generate the observed baryon asymmetry of the universe and the neutrino masses while playing a role in setting up Inflation. This is achievable with a triplet Higgs mass as low as 1 TeV, and predicts that the neutral component obtains a small vacuum expectation value $v_Δ<10$ keV. We find that our model has very rich phenomenology and can be tested by various terrestrial experiments as well as by astronomical observations. Particularly, we show that the successful parameter region may be probed at a future 100 TeV collider, upcoming lepton flavour violation experiments such as Mu3e, and neutrinoless double beta decay experiments. Additionally, the tensor-to-scalar ratio from the inflationary scenario will be probed by the LiteBIRD telescope, and observable isocurvature perturbations may be produced for some parameter choices. In this article, we present all the technical details of our calculations and further discussion of its phenomenological implications.
The Standard Model (SM) of Particle Physics cannot account for the long-standing conundrums of the nature of dark matter (DM) and of the obvious imbalance between matter and antimatter in our Universe. Therefore, in this work, I will discuss the Inert Doublet Model (IDM), augmented with higher-dimensional operators, tied either to the SM gauge sector and inducing CP violation or to the SM Higgs sector. In addition to identifying the parameter space for the observed DM relic abundance, we investigate the potential of this operator for giving rise to the measured baryon asymmetry during a multi-step electroweak phase transition. We find that the discussed extension of the IDM can, in principle, serve as an effective theory in which both DM and baryogenesis are accounted for.
Topological defects can act as local impurities that seed cosmological phase transitions. In this talk we will focus on how domain walls can affect the electroweak phase transition in the minimal singlet-scalar extension of the SM (xSM) with a $Z_2$ symmetry. When the transition is two-step, the early breaking of the $Z_2$ implies the formation of domain walls which subsequently act as seeds for the second step. The rate of the seeded phase transition can be evaluated within a 3d theory on the domain wall surface, and it is generically faster when compared to the standard homogeneous nucleation. We will comment on phenomenological implications for gravitational waves and baryogenesis.
Gravitational force can be obtained by gauging the Poincaré group.
The resulting theory is known as Einstein-Cartan (-Sciama-Kibble) gravity. In the absence of matter, it is indistinguishable from general relativity. The situation changes when matter is considered. In this talk, I will discuss the Einstein-Cartan theory and a novel mechanism for producing singlet fermions in the early Universe.
The Galactic center excess (GCE) remains one of the most intriguing discoveries from the Fermi Large Area Telescope (LAT) observations. I will revisit the characteristics of the GCE by first showing a new set of high-resolution galactic diffuse gamma-ray emission templates. This diffuse emission, which accounts for the bulk of the observed gamma rays, is ultimately due to cosmic-ray interactions with the interstellar medium. Using recent high-precision cosmic-ray observations, in addition to the continuing Fermi-LAT observations and observations from lower energy photons, we constrain the properties of the galactic diffuse emission. I will describe a large set of diffuse gamma-ray emission templates which account for a very wide range of initial assumptions on the physical conditions in the inner galaxy. I will discuss the updated spectral and morphological properties of the GCE coming from this new set of templates and the implications on the interpretation of the GCE. In particular, a high-energy tail is found at higher significance than previously reported. This tail is very prominent in the northern hemisphere, and less so in the southern hemisphere. This strongly affects one prominent interpretation of the excess: known millisecond pulsars are incapable of producing this high-energy emission, even in the relatively softer southern hemisphere, and are therefore disfavored as the sole explanation of the GCE. The annihilation of dark matter particles of mass $40^{+10}_{-7}$ GeV (95$\%$ CL) to $b$ quarks with a cross-section of $\sigma v = 1.4^{+0.6}_{-0.3} \times 10^{-26}$ cm$^{3}$s$^{-1}$ provides a good fit to the excess especially in the relatively cleaner southern sky. Dark matter of the same mass range annihilating to $b$ quarks or heavier dark matter particles annihilating to heavier Standard Model bosons can combine with a subdominant millisecond pulsars component to provide a good fit to the southern hemisphere emission as well, as can a broken power-law spectrum which would be related to recent cosmic-ray burst activity.
Spinning black holes (BHs) can efficiently transfer energy to the surrounding environment via superradiance. In particular, when the Compton length of a particle is comparable to the gravitational radius of a BH, the particle's occupation number can be exponentially amplified. In this talk, I will discuss the effect of the primordial-black-hole (PBH) superradiant instabilities on the generation of heavy bosonic dark matter (DM) with mass above 1 TeV. I will show that superradiance can significantly increase the DM density produced by PBHs with respect to the case that only considers Hawking evaporation, and hence lower initial PBH densities are required.
The nature of dark matter, one of the major components of the cosmic standard model, remains one of the outstanding problems in physics. One interesting model is scalar field dark matter (SFDM), which fits naturally into observations in both particle physics and cosmology. Simulations and calculations using SFDM often use a classical field approximation (MFT) of the underlying quantum field theory. And while it is suspected that large occupation numbers make this description good in the early universe, it is possible that this approximation fails during nonlinear structure growth and begins to admit important quantum corrections. To investigate this possibility, we compare simulations using the MFT to those that take into account these corrections. By studying their behavior as we scale the total number of particles in the system we can estimate how long the MFT remains an accurate description of the system. We estimate this time scale for a typical halo may be of order ~1 Gyr, short compared to the age of the universe. In this talk we will explain how these simulations are performed, as well as their results, and their potential implications.
Current data is consistent with our Universe living in a long-lived metastable state. In the early Universe (at high Hubble rates), the decay rate can be enhanced which imposes constraints on physics beyond the standard model. Thus, precise decay rate calculations become relevant. I will show how to consistently take quantum corrections into account through two different methods. One consists of using semi-classical methods to compute the Hawking-Moss decay rate at one loop, and the other modifies the standard stochastic formalism by considering the constraint effective potential.
Particle models beyond the Standard Model are often accompanied by the spontaneous breaking of a new symmetry and thus by a phase transition. Arguably, the most interesting among them are first order phase transitions, in which bubbles of the low-temperature phase form and collide, leading to the generation of gravitational waves (GWs). These might be measurable as stochastic GW background today and thus constitute a potential probe of new physics.
Consequently, analyzing models for their potential GW signal has gained much interest with the first measurements of GWs from astrophysical sources.
However, one has to ensure that these events do not interfere with other cosmological processes. In this talk we discuss the impact that GWs originating from a post BBN first order phase transition can have on structure formation.
We will show in which way the GW density affects the primordial density perturbations and derive a modified linear matter power spectrum that allows us to set limits on the strength and duration of such a late first order phase transition.
We discuss the possibility to measure particle couplings with stochastic gravitational wave backgrounds (SGWBs). Under certain circumstances a sequence of peaks of different amplitude and frequency - a stairway - emerges in a SGWB spectrum, with each peak probing a different coupling. The detection of such signature opens the possibility to reconstruct couplings (spectroscopy) of particle species involved in high energy phenomena generating SGWBs. Stairway-like signatures may arise in causally produced backgrounds in the early Universe, e.g. from preheating or first order phase transitions. As a proof of principle we study a preheating scenario with an inflaton ϕ coupled to multiple daughter fields {χj} with different coupling strengths. As a clear stairway signature is imprinted in the SGWB spectrum, we reconstruct the relevant couplings with various detectors.
Nowadays, the search for primordial gravitational waves is mainly focused on the parity-odd polarization pattern in the CMB the B-modes. A correct interpretation of B-mode measurements strongly relies on understanding their production mechanism. One intriguing scenario is gravitational waves generation by gauge fields. This talk describes the viability of inflation with a spectator sector comprised of non-Abelian gauge fields coupled through a higher order operator. I will discuss the theoretical restrictions for the amplitude and tensor tilt for chiral gravitational waves as well as the maximum possible enhancement of the gravitational wave background with respect to the one coming from vacuum fluctuations.
I will describe gravitational wave (GW) production during preheating in hybrid inflation models where an axion-like waterfall field couples to Abelian gauge fields. Based on a linear analysis, I will show that the GW signal from such models can be within the reach of a variety of foreseeable GW experiments such as LISA, AEDGE, ET and CE, and is close to that of LIGO A+, both in terms of frequency range and signal strength. Furthermore, the resultant GW signal is helically polarized and thus may distinguish itself from other sources of stochastic GW background. Finally, such models can produce primordial black holes that can compose dark matter and lead to merger events detectable by GW detectors.
Higgs precision measurements and resonance searches at the LHC have made sharper than ever the electroweak naturalness problem. In response, the particle physics community has begun to question symmetry-based solutions. We provide a new perspective by proposing a symmetry-based framework which does not require any fine-tuning to comply with current experimental observations. This is achieved by abandoning the additional constraint of minimality typically imposed on the structure of symmetry breaking. Single-Higgs coupling deviations of a few percent and trilinear self-coupling deviations of order one are irreducible in the natural parameter space.
We investigate the predictions for various nucleon decay rates in non-supersymmetric SU(5) models, where the masses of the third and second family down-type quarks and charged leptons each stem dominantly from single GUT operators and present a "fingerprinting" method to distinguish between GUT models with different flavor structure with the use of future experimental nucleon decay results.
In this talk I will discuss recent results [1] on the mass scales in the $SO(10)$ grand unified theory based on the following minimal Higgs representation content: adjoint $45_H$, spinor $16_H$ and complex vector $10_H$, with higher-dimensional operators on top of renormalizable interactions. Consistency of the theory requires a scalar doublet leptoquark, a scalar gluon octet and a scalar weak triplet to lie below $10$ TeV energy [1] and potentially accessible even at the LHC. In particular, the latter naturally induces a deviation in $W$-mass from its Standard Model value [2], relevant for the recent CDF-measurement.
These signatures are intimately connected with the prediction of proton lifetime below $10^{35}\rm yr$, to be probed in the new generation of proton decay experiments.
It is remarkable that the matter fields in the Standard Model (SM) are apparently unified into the SU(5) representations. A straightforward explanation of this fact is to embed all the SM gauge groups into a simple group containing SU(5), i.e., the grand unified theory (GUT). Recently, however, a new framework “fake GUT” has been proposed. In this new framework, the apparent matter unification can be explained by a chiral gauge group G, G ⊃ SU(5). We emphasize that the SM matter fields are not necessarily embedded into the chiral representations to explain the apparent unification. In this paper, we discuss details of concrete realizations of the fake GUT model. We first study the model based on SU(5) × U(2)H , where SU(3)c in the SM is from SU(5) while SU(2)L × U(1)Y are from the diagonal subgroups of SU(5) × U(2)H .We also extend this model to the one based on a semi-simple group, SU(5) × SU(3)H , so that U(2)H is embedded in SU(3)H. We also show that this framework predicts rather different decay patterns of the proton, compared to the conventional GUT.
Magnetic monopoles are inevitable predictions of GUT theories. They are produced during phase transition in the early universe, but also mechanisms like Schwinger effect in strong magnetic fields could give relevant contributions to the monopole number density. I will show that from the detection of intergalactic magnetic fields of primordial origin we can infer additional bounds on the magnetic monopole flux at present time. I will also discuss the implications of these bounds for monopole pair production in primordial magnetic fields.
The axionic inflaton with the Chern–Simons coupling may generate U(1) gauge fields and charged particles simultaneously. In order to incorporate the backreaction from the charged particles on the gauge fields, we develop a procedure to obtain an equilibrium solution for the gauge fields by treating the induced current as effective electric and magnetic conductivities. Introducing mean field approximation, and numerically solving self-consistency equations, we find that the gauge field amplitudes are drastically suppressed. Interestingly, as the production becomes more efficient, the charged particles gain a larger part of the transferred energy from the inflaton and eventually dominate it. Our formalism offers a basis to connect this class of inflationary models to a rich phenomenology such as baryogenesis and magnetogenesis.
The interaction between axion and gauge fields has been discussed in the contexts of inflationary models and primordial gravitational production. In this talk, we consider an inflationary model where SU(N) gauge fields couple to the inflaton through the Chern-Simons term. I will shortly review the dynamics of SU(2) gauge fields during inflation and then provide a general procedure to construct homogeneous and isotropic solutions of SU(N) gauge fields. I will also show the results for the linear perturbations in our model and discuss open questions. It is straightforward to apply our procedure to the other simple Lie groups.
Heavy, unstable, and out-of-equilibrium particles with a matter equation of state appear in many well-motivated cosmological histories; examples include the inflaton condensate and moduli fields. Decays of the matter component result in highly relativistic non-thermal SM particles that must subsequently attain thermal equilibrium. We focus on cascades of $2 \to 3$ gauge interactions of the SM as the primary means of thermalization at high energies. Paying particular attention to coherent plasma effects and the role of the decaying particle's mass and branching ratios, we study the energy-spectra of SM particles emerging from the thermalization cascade. Finally, we comment on potential applications of such energetic non-thermal particles in cosmology and, in particular, heavy DM production.
If gauge fields are coupled to an axion field during the inflationary epoch, they can lead to unique observational signatures. However, this system often shows strong backreaction effects, invalidating the standard perturbation theory approach. In this work, we present the first nonlinear lattice simulation of an axion-U(1) system during inflation. We use it to fully characterize the statistics of the comoving curvature perturbation $\zeta$. We use the simulation to characterize the statistics of the comoving curvature perturbation $\zeta$ at the full nonlinear level. Our results invalidate previous bounds coming from overproduction of primordial black holes, allowing for an observable gravitational waves signal at interferometer scales. Our work shows that simulations of this kind can be a crucial tool to understand the phenomenology of the inflationary era and to compute observables from it.
In the quest for unification of the Standard Model with gravity, classical scale invariance can be utilized to dynamically generate the Planck mass and the inflaton potential. However, the generation of the vastly separated electroweak scale requires further explanation. We use the Coleman- Weinberg mechanism in an additional scalar sector as a unified origin for dynamical generation of both scales. The link to the electroweak scale is established by the neutrino option where the Higgs potential is radiatively generated by right-handed neutrinos and also the active SM neutrinos are given a mass by the type-I seesaw mechanism. The inflationary CMB observables are predicted to interpolate between those of Starobinksy and linear chaotic inflation model.
The detection of coherent elastic neutrino-nucleus scattering (CE$\nu$NS) opens up new opportunities for neutrino physics within and beyond the standard model. Following the initial discovery at a spallation source in 2017, several experimental attempts are currently striving to detect it with a broad variety of modern detection technologies at reactor-site. As a leading reactor experiment, CONUS aims at an observation in the regime of fully coherent interaction with antineutrinos emitted from the powerful $3.9$ GW$_{\mathrm{th}}$ reactor core of the nuclear power plant in Brokdorf (Germany). In particular, the application of ultra-low threshold, high-purity germanium detectors within a compact shield in close proximity to a nuclear reactor core represents another milestone on the road towards high-statistics neutrino physics. The acquired and future CONUS data sets allow further investigations of yet undetected neutrino interaction channels and electromagnetic properties. This talk will address constraints on beyond the standard model neutrino phenomenology that arise from the first two CONUS data collection periods. Bounds on non-standard neutrino-quark interactions of vector and tensor type from CE$\nu$NS are presented, and the parameter space of simplified scalar and vector mediators that is probed by CE$\nu$NS and elastic neutrino-electron scattering is discussed. Limits on an effective neutrino magnetic moment and an effective neutrino millicharge are also given. Finally, we discuss further investigation possibilities with current and future CE$\nu$NS data and the advantage of measurements with different neutrino sources as well as different target materials.
Coherent elastic neutrino nucleus scattering (CEvNS) is a well-predicted Standard Model process only recently observed for the first time. Its precise study could reveal non-standard neutrino properties and open a window to search for physics beyond the Standard Model.
NUCLEUS is a CEvNS experiment conceived for the detection of neutrinos from nuclear reactors with unprecedented precision at recoil energies below 100 eV. Thanks to the large cross-section of CEvNS, an extremely sensitive cryogenic target of 10g of CaWO4 and Al2O3 crystals is sufficient to provide a detectable neutrino interaction rate.
NUCLEUS will be installed between the two 4.25 GW reactor cores of the Chooz-B nuclear power plant in the French Ardennes, which provide an anti-neutrino flux of 1.7 x 10^12 v/(s cm2). At present, the experiment is under construction. The commissioning of the full apparatus is scheduled for 2022, in preparation for the move to the reactor site.
Non-standard neutrino interactions with a massive boson can produce the bosons in the core of core-collapse supernovae (SNe). After the emission of the bosons from the SN core, their subsequent decays into neutrinos can modify the SN neutrino flux. We show future observations of neutrinos in a next galactic SN in Super-Kamiokande (SK) and Hyper-Kamiokande (HK) can probe flavor-universal non-standard neutrino couplings with a boson sveral orders beyond the constraint from excessive energy loss of SN 1987A neutrino burst. We also discuss sensitivity of flavor-universal non-standard neutrino interactions in future observations of diffuse neutrinos from all past SNe, known as the diffuse supernova neutrino background (DSNB). In our analysis, observations of neutrinos in all past SNe in HK, JUNO and DUNE experiments can probe such couplings a factor of $\sim 2$ beyond the SN 1987A constraint. However, our prediction could include uncertainty lager than a factor of $\sim 2$ due to the difficulty of the estimation of diffuse neutrino flux from all past SNe.
We present a generic structure (the layer structure) for decoherence effects in neutrino oscillations by combining the concept of the open quantum system and quantum field theory, which includes and parameterize decoherence effects from quantum mechanical and classical uncertainties. With the help of the layer structure, we classify the former as state decoherence (SD) and the latter phase decoherence (PD), then further conclude that both SD and PD result from phase wash-out effects of different phase structures on different layers. Such effects admit for simple numerical calculations of decoherence for a given width and shape of uncertainties. While our structure is generic, so are the uncertainties, nonetheless, a few notable ones are: the wavepacket size of the external particles, the effective interaction volume at production and detection, the energy reconstruction model and the neutrino production profile. Furthermore, we estimate the experimental sensitivities for SD and PD, parameterized by the uncertainty parameters, for reactor neutrinos and decay-at-rest neutrinos, using a traditional rate measuring method and a novel phase measuring method.
A core-collapse supernova (SN) offers an excellent astrophysical laboratory to test non-zero neutrino magnetic moments. In particular, the neutronization burst phase, which lasts for few tens of milliseconds post-bounce, is dominated by electron neutrinos and can offer exceptional discovery potential for transition magnetic moments. We simulate the neutrino spectra from the burst phase in forthcoming neutrino experiments like the Deep Underground Neutrino Experiment (DUNE), and the Hyper-Kamiokande (HK), by taking into account spin-flavour conversions of SN neutrinos, caused by interactions with ambient magnetic fields. We find that the neutrino transition magnetic moments which can be explored by these experiments for a galactic SN are an order to several orders of magnitude better than the current terrestrial and astrophysical limits. Additionally, we also discuss how this realization might shed light on three important neutrino properties: (a) the Dirac/Majorana nature, (b) the neutrino mass ordering, and (c) the neutrino mass-generation mechanism.
Due to neutrino-neutrino forward scattering, the neutrino flavor conversion inside a supernova is still an open question. This type of interaction leads to a non-linear evolution of neutrino states and is strongly dependent on their angular distribution. Thus, the peculiarities of the supernovae's innermost environment impose a number of complexities on an accurate calculation of the neutrino evolution towards the outside of the star. Unquestionably, a comprehensive understanding of the neutrino flavor conversion mechanisms is essential to extract astrophysical information from future detections of supernovae neutrinos. Therefore, we present some preliminary results for this problem, in which we have adopted a numerical solution approach. First, we discuss an isotropic neutrino gas and its connection to simpler systems, such as a pendulum. Then, we show the results of modeling the supernova neutrino emission as a sphere (Bulb-Model), which has connections with the isotropic scenario when considering a single-angle emission approximation. Finally, we explain the limitations of this model and the next steps toward a more detailed calculation. A novelty of our work is the open-source nature of our code, already available at public repositories, allowing those interested in neutrino collective effects to reproduce our results.
The Belle II experiment will measure the rare decays B → K νν and B → K νν with increased sensitivity which can hence be expected to serve as a very efficient probe of new physics. We calculate the relevant branching ratios in low-energy effective field theory including an arbitrary number of massive sterile neutrinos and discuss the expected sensitivity to the different operators. We also consider the longitudinal polarization fraction FL and the inclusive decay rate B → Xs νν.
In our investigation we consider new physics dominantly contributing to one and two operators both for massless and massive (sterile) neutrinos. Our results show a powerful interplay of the exclusive decay rates B → K νν and B → K νν, and a surprisingly large sensitivity of the inclusive decay mode to vector operators even under conservative assumptions about its uncertainty. Furthermore, the sensitivity of FL is competitive with the branching ratio of B → K* νν in the search for new physics contributing to scalar operators and thus also complementary to B → K νν and B → Xs νν.
I will briefly review the current status of the anomaly in the lepton flavour universality ratios $R_{D^{(*)}}$. Subsequently, I will discuss opportunities to probe the underlying New Physics with targeted LHC searches.
In this talk I plan to discuss how a scalar leptoquark addressing the charged current flavour anomalies can also serve as a mediator to the dark sector. Starting from the parameter space favoured by the flavour fit, I will discuss the constraints from collider searches, dark matter direct detection and the relic density, pointing the delicate interplay between them. Part of the parameter space can accommodate thermal freeze-out (WIMP), but in other regions the "Conversion Driven Freeze-Out" (CDFO) mechanism is the dominant production mode of dark matter in the early Universe.
Non-leptonic $B$ decays offer a powerful probe for testing the Standard Model description of CP violation. Particularly interesting are the $B^0_s\to D_s^\mp K^\pm$ decays, originating from pure tree topologies, which allow a theoretically clean determination of the angle $\gamma$ of the Unitarity Triangle. Intrigued by an LHCb analysis, showing tension with other extractions of $\gamma$, we shed more light on this situation. Extracting the individual branching ratios of the $B^0_s\to D_s^\mp K^\pm$ channels and combining them with information from semileptonic $B^0_{(s)}$ decays, we arrive at yet another puzzling situation, which actually agrees with decays that have similar dynamics. In view of these puzzles, we extend our analysis in order to allow for New Physics. We develop a model-independent formalism to include New Physics effects and apply it to the current experimental data. We find that New Physics contributions as small as about $30 \%$ of the Standard Model amplitudes could accommodate the data. The proposed strategy sets the stage for future analyses, making it exciting to see whether in the high-precision era of $B$ physics ahead of us new sources of CP violation will finally be established.
The Belle II experiment at the SuperKEKB energy-asymmetric e+e− collider is a substantial upgrade of the B factory facility at the Japanese KEK laboratory. The design luminosity of the machine is 6×1035 cm−2s−1 and the Belle II experiment aims to ultimately record 50 ab−1 of data, a factor of 50 more than its predecessor. With this data set, Belle II will be able to measure the Cabibbo-Kobayashi-Maskawa (CKM) matrix, the matrix elements and their phases, with unprecedented precision and explore flavor physics with rare decays of B and charmed mesons. In this presentation, we will review the latest results from Belle II related to B and charm decay.
Black holes are considered to be exceptional due to their time evolution and information processing. However, it was recently proposed that these properties are generic for objects, the so-called saturons, that attain the maximal entropy permitted by unitarity. We verify this connection within a renormalizable $SU(N)$ invariant theory. We also review the concept of saturation of the universal micro-state entropy bound. We demonstrate that in the above theory, despite the absence of gravity, the bubbles, representing saturated bound states of $SU(N)$ Goldstones, exhibit properties that are in one-to-one correspondence to those of black holes. Additionally, we discuss the memory burden effect, by which a system is stabilized by the quantum information contained within it. This has important implications for black holes and saturons in general.
We discuss the correspondence Between Black holes and Saturons, states that attain the maximal entropy permitted by unitarity. We present the connection within a renormalizable SU(N) invariant theory. We show that the spectrum contains a tower of bubbles representing bound states of SU(N) Goldstones. We argue that a saturated bound state exhibits a striking resemblance with a black hole. The Bekenstein-Hawking formula gives the saturon entropy. Semiclassically, they possess an information horizon. They evaporate at a thermal rate with a temperature proportional to their inverse radius. The information retrieval time is equal to Page’s time. We discuss the fundamental and observational implications of the black hole–saturon correspondence.
Oscillons are oscillating, localized configurations in real scalar field theories. They appear in potentials that are shallower than quadratic away from the minimum and can be extremely long-lived.
Since plateau models are of great relevance for inflation, oscillons have been shown to form efficiently during preheating in a wide range of such models.
Most work on oscillons has focused on single-field dynamics, however, various theories of fundamental physics that go beyond the Standard Model suggest the presence of a multitude of scalar fields in the early Universe. In this talk, I will describe the work I performed on the dynamics of oscillons in multi-field theories.
In particular, I will show how to construct multi-field oscillons in the non-relativistic limit of scalar field theories, and use this formalism to explain the origin of their stability and long lifetimes in one specific model. I will talk about my most recent work in which I show that instabilities in the quantum vacuum can naturally lead to the condensation of multi-field oscillons. This is of special interest in the context of preheating scenarios, but could also find other applications in cosmology.
Finally, I will comment on strategies for generalizing this work to other models, for example, models with an arbitrary number of fields.
Coherent states are generally deemed to be adequate quantum counterparts to classical configurations and their evolution provides a good description of systems in which cumulative quantum effects could lead to the break-down of the classical description. In this talk, by focussing on a $\lambda \phi^4$ theory, I will discuss the dynamics of the coherent state corresponding to a homogeneous condensate of scalar bosons, with a particular focus on the quantum depletion of the one-point function of the system. I will show that the main depletion channel is determined by the annihilation of four condensate constituents into two relativistic quanta. Moreover, I will discuss the advantage of constructing the state explicitly in its entirety, which gives a unique perspective on the well-known divergences of the initial field energy and acceleration, that systems with certain initial conditions experience.
We study kink-antikink scattering in the sine-Gordon model in the presence of interactions with an additional scalar field, ψ, that is in its quantum vacuum. In contrast to the classical scattering, now there is quantum radiation of ψ quanta and the kink-antikink may form bound states that resemble breathers of the sine-Gordon model. We quantify the rate of radiation and map the parameters for which bound states are formed. Even these bound states radiate and decay, and eventually there is a transition into long-lived oscillons.
Various precision observables, such as flavour changing decays, are
generated at one-loop level in the Standard Model and their
renormalisation involves cancellations between purely bosonic and
fermionic interactions. In this talk I will show how perturbative
unitarity constraints can be used to derive renormalised matching
conditions for generic theories. These general results comprise the
matching conditions for specific models that address current flavour
anomalies and can be used for phenomenological analyses.
I will argue that black holes admit vortex structure. This is based both on a graviton-condensate description of a black hole as well as on a correspondence between black holes and generic objects with maximal entropy compatible with unitarity, so-called saturons. Due to vorticity, a Q-ball-type saturon of a calculable renormalisable theory obeys the same extremality bound on the spin as the black hole. Correspondingly, a black hole with extremal spin emerges as a graviton condensate with vorticity. This offers a topological explanation for the stability of extremal black holes against Hawking evaporation. Next, I will comment on possible phenomenological consequences.
We study the nonlinear realization of supersymmetry in a dynamical/cosmological background in which derivative terms like kinetic terms are finite. Starting from linearly realized theories, we integrate out heavy modes without neglecting derivative terms to obtain algebraic constraints on superfields. Thanks to the supersymmetry breaking contribution by the kinetic energy, the validity of constrained superfields can be extended to various cosmological situations beyond the SUSY breaking in vacuum and inflation, including reheating, kination, the standard and kinetic axion misalignment, and cosmological relaxation.
Particles coupled to inflaton have effective time-dependent masses due to the background inflaton field, which leads to the creation of the particles from the vacuum via non-perturbative processes known as preheating. We consider the decay process of such dressed particles by using the Furry perturbation theory, where the time-dependent mass is treated non-perturbatively whereas the interactions between dressed particles perturbatively. We show that we can reproduce the decay process expected from un-dressed particle scattering. Furthermore, we find a daughter particle production process that is naively forbidden kinematically. We discuss its relation to instant preheating scenario.
We consider a massless minimally coupled quantum scalar field with an asymmetric (quartic plus cubic) self interaction,
V (φ) = λφ^4/4!+βφ^3/3! in the (3 + 1)-dimensional inflationary de Sitter background. This potential is bounded from below
regardless of the sign of β. The motivation of this study comes from the fact that such a potential may generate negative vacuum expectation value of V(φ) at late time, thereby decreasing the value of cosmological constant which is essential to end the inflation. We investigate this theory via Starobinsky stochastic technique and compare it with the field theoretic results upto O(λ^2) and O(λβ^2). We compute the vacuum expectation value of φ, φ^2, V(φ) and a non-perturbative as well as stochastic computation of the dynamically generated mass. We also estimate the possible shift of the inflationary cosmological constant due to this potential V(φ).
The $R^2$-Higgs inflation is one of the best fit model to the data from Planck experiment. We show that the inflationary dynamics of $R^2$-Higgs inflation with two Higgs doublets favors nearly degenerate mass spectra for additional Higgs bosons. While satisfying all constraints from Planck 2018 data, such inflationary scenario leaves unique signatures for ongoing and future collider experiments.
There are interesting connections between searches for long-lived particles (LLPs) at the LHC and early universe cosmology. We study the non-thermal production of ultra-relativistic particles (i.e. dark radiation) in the early universe via the decay of weak-scale LLPs. The cosmologically interesting parameter space we find corresponds to LLP decay lengths which lie at the boundary between prompt and displaced signatures at the LHC and can be comprehensively explored by combining searches for both. To illustrate this point, we consider a scenario where the LLP decays into a charged lepton and a (nearly) massless invisible particle. By reinterpreting searches for promptly decaying sleptons and for displaced leptons at both ATLAS and CMS we can then directly compare LHC exclusions with cosmological observables. We find that the CMB-S4 target value of $\Delta N_\text{eff}=0.06$ is already excluded by current LHC searches and even smaller values can be probed for LLP masses at the electroweak scale.
The charged wino decay plays an important role in the search for supersymmetric particles in accelerator experiments. We performed full one-loop calculation of the charged wino decay rate, which has not been done before, and improved the accuracy of theoretical predictions. By incorporating the effects of chiral perturbation theory and various quantum corrections, I will discuss that the decay rate is corrected by a few percent from the tree level calculation.
We study the freeze-in of gravitationally interacting dark matter in extra-dimensions. Focusing on a minimal dark matter candidate that only interacts with the SM via gravity a five dimensional model we find that a large range of dark matter and Kaluza-Klein graviton masses can lead to the observed relic density. The preferred values of the masses and the strength of the interaction make this scenario very hard to text in terrestrial experiments. However, significant parts of the parameter space lead to warm dark matter and can be tested by cosmological and astrophysical observations.
If the mediator of a $t$-channel process is allowed to be on its mass-shell, the matrix element becomes singular, leading to infinite cross section. In the case of a stable, massive mediator neither IR-regularization methods nor decay width can be used to regularize the divergence.
This issue has not been extensively discussed in the existing literature, even though it affects processes that are already present in the Standard Model of particle physics. The natural context of the problem are, however, SM extensions that provide massive, stable dark matter candidates.
In my talk, I will formulate precise conditions for the singularity to occur in a given process and present examples of singular processes both in the SM and beyond it. Then, I will demonstrate a solution, developed within thermal field theory, that allows to calculate mediator's effective width regularizing the divergence.
In this talk I will discuss the influence of non-perturbative effects,
namely Sommerfeld enhancement and bound state formation, on the cosmological production of non-thermal dark matter (DM). For this purpose, I will focus on a class of simplified models with t-channel mediators. These naturally combine the requirements for large corrections in the early Universe, i.e. beyond the Standard Model states with long range interactions, with a sizable new physics production cross section at the LHC.
I will show that the dark matter yield of the superWIMP mechanism is suppressed considerably due to the non-perturbative effects under consideration, which leads to a significant shift in the cosmologically preferred parameter space of non-thermal dark matter in these models. By revisiting the implications of LHC bounds on long-lived particles associated with non-thermal dark matter, I will conclude that testing this broad class of DM models at the LHC and its successors is a bigger challenge than previously anticipated.
The increasing need of numerical predictions for dark matter models is not always easy to satisfy looking at the software available today. With this work, we present a C++
code to compute 2 to 2 squared scattering amplitudes using MARTY
. The numerical library generated in this way has been enriched with additional features, aiming at allowing the user to easily include and use such a library in external softwares. We restricted ourselves to the tree-level amplitudes in the MSSM relevant to solve the Boltzmann equation in a freeze-out scenario. Future development of this work will provide a direct interface with SuperIso Relic
and the possibility to choose more general models.
The enhancement of the spectrum of primordial comoving curvature perturbation R can induce the production of primordial black holes (PBH) which could account for part of present day dark matter. As an example of the effects of the modification of gravity on the production of PBHs, we investigate the effects on the spectrum of R produced by the modification of gravity in the case of G-inflation, deriving the relation between the unitary gauge curvature perturbation ζ and the comoving curvature perturbation R, and identifying a background dependent enhancement function E which can induce large differences between the two gauge invariant variables. We use this relation to derive an equation for R, showing for the presence of a momentum dependent effective sound speed (MESS), associated to the intrinsic entropy which can arise in modified gravity theories, in agreement with the model independent MESS approach to cosmological perturbations. When ζ is not constant in time it is different from R, for example on sub-horizon scales, or in models exhibiting an anomalous super-horizon growth of ζ, but since this growth cannot last indefinitely, eventually they will coincide. We derive the general condition for super-horizon growth of ζ, showing that slow-roll violation is not necessary. Since the abundance of PBHs depends on the statistics of the peaks of the comoving density contrast, which is related to the spectrum of R, it is important to take into account these effects on the PBHs abundance in modified gravity theories.
Many extensions of the Standard Model feature spontaneously broken new symmetries that give rise to bosonic particles with naturally small masses and couplings, so-called axion-like particles (ALPs). In my talk I will discuss the case of MeV-scale ALPs, which are predicted to be long-lived on the time scales relevant for particle physics and cosmology. A particular focus will be on lifetimes in the range of (thousands of) years, for which decaying ALPs can have an observable effect on the Cosmic Microwave Background and primordial element abundances. I will discuss how to constrain such ALPs using astrophysical and cosmological data and show that there remains viable parameter space for the case of non-thermal ALPs.
Axion-like-particle (ALP) is a well-motivated candidate for dark matter, and it has been subject to extensive theoretical and experimental research in recent years. The most popular ALP production mechanism studied in the literature is the misalignment mechanism, where the ALP field has negligible kinetic energy initially, and it starts oscillating when its mass becomes comparable to the Hubble scale. Recently, a new mechanism called Kinetic Misalignment has been proposed where the ALP field receives large kinetic energy at early times due to the explicit breaking of the Peccei-Quinn symmetry. This causes a delay in the onset of oscillations so that the ALP dark matter parameter space can be expanded to lower values of the axion decay constant. At the same time, the ALP fluctuations grow exponentially via parametric resonance in this setup, and most of the energy in the homogeneous mode is converted to ALP particles. This process in known as fragmentation. In this talk, I will discuss the observational consequences of fragmentation for the axion miniclusters, and show that a sizable region of the ALP parameter space can be tested by future experiments that probe the small-scale structure.
We investigate the effect of quantum loops on the theory of axionlike particles (ALPs) coupled to electrons. Contrary to some statements in the recent literature, the effective ALP-photon coupling induced by an electron loop can be sizeable in the plasma of a supernova. We define a general effective coupling that depends on the kinematics of the specific process in which an ALP scatters, decays, or is produced. Using this effective coupling, it can be shown that production of ALPs by loop processes is in fact slightly more efficient than the respective tree-level processes in a numerical model of SN1987A. We update the bound on $ g_{ae} $ imposed by the observed duration of the neutrino burst of SN1987A. Moreover, we derive a new bound, which does not exist at tree-level for ALPs only coupled to electrons, from the non-observation of gamma-rays from ALP decays directly after the initial neutrino burst was observed in 1987. These are the leading constraints on $ g_{ae} $ in the ALP-mass range of roughly $ 30 \text{ keV} $ to $ 300 \text{ MeV} $.
Using the effective coupling, we furthermore point out that ALP dark matter coupled to electrons is not stable in the keV mass range due to loop-induced decays into photons. Large parts of the parameter space that direct detection experiments are sensitive to are therefore either (i) incompatible with the assumption of ALPs being dark matter as their lifetime is shorter than the age of the universe, or are (ii) already excluded by indirect detection searches for x-rays and gamma-rays as products of ALP decays.
Axions are fast becoming one of the most popular solutions to the dark matter problem. Neutron stars offer an exciting opportunity to detect radio lines produced by axion dark matter which converts into photons in the plasma around the star. In recent years, many groups have begun searching neutron star populations for a tell-tale radio line produced by axions. In this talk I will give an update both on the recent developments on modelling the dark matter signal and describe the radio searches which have been undertaken to find it.
The axion provides a solution for the strong CP problem and is one of the leading
candidates for dark matter. In this talk, we propose an axion detection scheme based
on quantum nondemolition detection of magnons, i.e., quanta of collective spin
excitations in a ferromagnetic crystal. Furthermore, we give an upper limit on the
coupling constant between an axion and an electron for a certain mass of the axion
dark matter.
In this talk I will show that the strong CP problem is solved in a large class of compactifications of string theory. The Peccei-Quinn mechanism solves the strong CP problem if the CP-breaking effects of the ultraviolet completion of gravity and of QCD are small compared to the CP-preserving axion potential generated by low-energy QCD instantons. We characterize both classes of effects. To understand quantum gravitational effects, we consider an ensemble of flux compactifications of type IIB string theory on orientifolds of Calabi-Yau hypersurfaces in the geometric regime, taking a simple model of QCD on D7-branes. We show that the D-brane instanton contribution to the neutron electric dipole moment falls exponentially in $N^4$, with $N$ the number of axions. In particular, this contribution is negligible in all models in our ensemble with N>17. We interpret this result as a consequence of large N effects in the geometry that create hierarchies in instanton actions and also suppress the ultraviolet cutoff. We also compute the CP breaking due to high-energy instantons in QCD. In the absence of vectorlike pairs, we find contributions to the neutron electric dipole moment that are not excluded, but that could be accessible to future experiments if the scale of supersymmetry breaking is sufficiently low.
My talk will be based on arXiv:2108.05372,2203.11959. I will explain how we obtain the deconfinement temperature of thermal QCD-like theories at intermediate coupling from ${\cal M}$-theory dual inclusive of ${\cal O}(R^4)$ corrections. In this process we found certain novel features such as "UV-IR" mixing, "Flavor Memory" effect and non-renormalization of the deconfinement temperature beyond one-loop in the zero instanton sector. Further I shall explain how the deconfinement temerature of the thermal QCD-like theories will be modified in the presence of rotating Quark Gluon Plasma and and what will be the effect of vorticity on the novel features described earlier in the small frequency limit.
The study of cosmological singularities in the context of string theory has been widely addressed on different time-dependent spacetime backgrounds and has never proved completely successful. Here we investigate the Null Boost Orbifold, which reproduces a Big-Bang type singularity but unfortunately suffers from unusual divergences when dealing with scattering amplitudes both in the closed and open string sector. We trace back the origin of this pathological behaviour to the non-existence of a well-defined perturbative expansion into ordinary Feynman diagrams of the underlying effective QFT. Then we show that the introduction of a background Kalb-Ramond $B$-field, with the help of the well-known Seiberg-Witten map, may be the key towards the resolution of the singularity.
In my talk I will review the current status of higher and infinite derivative models of gravity heavily inspired and motivated by the String Field Theory. In particular I will address questions of unitarity of such models which are connected to works of Pius and Sen in SFT. Also potential renormalizability of these constructions as well as implication for the inflationary observables will be discussed with explicit predictions for deviation of the tensor-to-scalar ration and non-gaussianities.
The talk is mainly based on recent works in collaboration with Prof. Alexei Starobinsky, Dr. Sravan Kumar and Dr. Anna Tokareva 2003.00629, 2005.09550, 2103.01945, 2205.13332 and works in progress.
In this talk I will discuss higher order F^4-corrections on the type IIB scalar potential considering divisor topologies associated with Calabi Yau threefolds suitable for implementing the LARGE Volume Scenario for the moduli stabilization. I will focus on anlyzing the effects of such corrections on string inflationary model and, in particoular, on fiber and blow-up inflation. The obtained results will be compared with phenomenological observations and conditions on the parameters of the models will be given in order to preserve the inflationary dynamics and make the picture consistent.