Search

It is shown that the presence of an interaction between dark energy and dark matter can induce a transmutation of quintessence from thawing to scaling freezing. The analysis is done in a Lagrangian approach where dark energy and dark matter are treated as spin zero fields. Remarkably, with the cosmological constraints on energy densities of dark matter and dark energy, such a transmutation can occur in the late universe and searchable in accumulating cosmological data by DESI and other dark energy-related experiments. We give a fit to the dark energy equation of state which can be used by experimental collaborations to search for this transmutation that can occur at redshifts up to $z=13$ depending on the interaction strength. A transmutation in the range $z=1-3$ is already within reach of current and near future experiments., Comment: 6 pages, 4 figures (main) with supplemental material (7 pages, 5 figures)

The description of dark matter as a pressure-less fluid and of dark energy as a cosmological constant, both minimally coupled to gravity, constitutes the basis of the concordance $\Lambda\text{CDM}$ model. However, the concordance model is based on using equations of motion directly for the fluids with constraints placed on their sources, and lacks an underlying Lagrangian. In this work, we propose a Lagrangian model of two spin zero fields describing dark energy and dark matter with an interaction term between the two along with self-interactions. We study the background evolution of the fields as well as their linear perturbations, suggesting an alternative to $\Lambda$CDM with dark matter and dark energy being fundamental dynamical fields. The parameters of the model are extracted using a Bayesian inference tool based on multiple cosmological data sets which include those of Planck (with lensing), BAO, Pantheon, SH0ES, and WiggleZ. Using these data, we set constraints on the dark matter mass and the interaction strengths. Furthermore, we find that the model is able to alleviate the Hubble tension for some data sets while also resolving the $S_8$ tension., Comment: 42 pages, 10 figures and 2 tables (Accepted for publication in JCAP)

The standard approach of calculating the relic density of thermally produced dark matter based on the assumption of kinetic equilibrium is known to fail for forbidden dark matter models since only the high momentum tail of the dark matter phase space distribution function contributes significantly to dark matter annihilations. Furthermore, it is known that the computationally less expensive Fokker-Planck approximation for the collision term describing elastic scattering processes between non-relativistic dark matter particles and the Standard Model thermal bath breaks down if both scattering partners are close in mass. This, however, is the defining feature of the forbidden dark matter paradigm. In this paper, we therefore include the full elastic collision term in the full momentum-dependent Boltzmann equation as well as in a set of fluid equations that couple the evolution of the number density and dark matter temperature for a simplified model featuring forbidden dark matter annihilations into muon or tau leptons through a scalar mediator. On the technical side, we perform all angular integrals in the full collision term analytically and take into account the effect of dark matter self-interactions on the relic density. The overall phenomenological outcome is that the updated relic density calculation results in a significant reduction of the experimentally allowed parameter space compared to the traditional approach, which solves only for the abundance. In addition, almost the entire currently viable parameter space can be probed with CMB-S4, next-generation beam-dump experiments or at a future high-luminosity electron-position collider, except for the resonant region where the mediator corresponds to approximately twice the muon or tau mass., Comment: 24 pages, 6 figures; V2 corresponds to the published version

Hidden sectors are ubiquitous in supergravity theories, in strings and in branes. Well motivated models such as the Stueckelberg hidden sector model could provide a candidate for dark matter. In such models, the hidden sector communicates with the visible sector via the exchange of a dark photon (dark $Z'$) while dark matter is constituted of Dirac fermions in the hidden sector. Using data from collider searches and precision measurements of SM processes as well as the most recent limits from dark matter direct and indirect detection experiments, we perform a comprehensive scan over a wide range of the $Z'$ mass and set exclusion bounds on the parameter space from sub-GeV to several TeV. We then discuss the discovery potential of an $\mathcal{O}$(TeV) scale $Z'$ at HL-LHC and the ability of future forward detectors to probe very weakly interacting sub-GeV $Z'$ bosons. Our analysis shows that the parameter space in which a $Z'$ can decay to hidden sector dark matter is severely constrained whereas limits become much weaker for a $Z'$ with no dark decays. The analysis also favors a self-thermalized dark sector which is necessary to satisfy the dark matter relic density., Comment: 35 pages, 15 figures. Accepted for publication in JHEP

We summarize the state of Beyond the Standard Model (BSM) model building in particle physics for Snowmass 2021, focusing mainly on several whitepaper contributions to BSM model building (TF08) and closely related areas., Comment: 44 pages, 1 figure, Submitted to the Proceedings of the US Community Study on the Future of Particle Physics (Snowmass 2021). Topical Group Report for TF08 - BSM Model Building

This is the Snowmass2021 Energy Frontier (EF) Beyond the Standard Model (BSM) report. It combines the EF topical group reports of EF08 (Model-specific explorations), EF09 (More general explorations), and EF10 (Dark Matter at Colliders). The report includes a general introduction to BSM motivations and the comparative prospects for proposed future experiments for a broad range of potential BSM models and signatures, including compositeness, SUSY, leptoquarks, more general new bosons and fermions, long-lived particles, dark matter, charged-lepton flavor violation, and anomaly detection., Comment: 108 pages + 38 pages references and appendix, 37 figures, Report of the Topical Group on Beyond the Standard Model Physics at Energy Frontier for Snowmass 2021. The first nine authors are the Conveners, with Contributions from the other authors

Cosmic Probes of Fundamental Physics take two primary forms: Very high energy particles (cosmic rays, neutrinos, and gamma rays) and gravitational waves. Already today, these probes give access to fundamental physics not available by any other means, helping elucidate the underlying theory that completes the Standard Model. The last decade has witnessed a revolution of exciting discoveries such as the detection of high-energy neutrinos and gravitational waves. The scope for major developments in the next decades is dramatic, as we detail in this report., Comment: Report of theTopical Group on Cosmic Probes of Fundamental Physics, for the U.S. decadal Particle Physics Planning Exercise (Snowmass 2021)

In 2020 the XENON1T experiment observed an excess of events with an electron recoil energy $E_R$ in the range of $2\,$--$\,3\,$keV. Such an excess can arise from a variety of sources such as solar axions or a neutrino magnetic moment, but also from inelastic scattering of dark matter off the xenon atoms. The recoil energy of the electron then depends on the mass difference of the dark particles. In this paper we show that the annual modulation of both the event rate and the electron recoil energy provide important additional information that allows to distinguish among different theoretical explanations of the signal. To this end, we first extend the formalism of annual modulation to electronic recoils, inelastic dark matter scattering and the electron recoil energy. We then study a concrete theoretical model with two Dirac fermions and a dark photon. We take into account all relevant cosmological and experimental constraints on this model and apply it to the XENON1T and and XENONnT experiments with realistic detection thresholds, efficiencies and energy resolutions, fitting the main physical parameters of the model, i.e. the mass splitting and the electron scattering cross section. The discriminatory power of the additional information from the annual modulation of both the signal rate and the electron recoil energy is then demonstrated for XENONnT with a simplified model based on these main physical parameters. This more sensitive procedure compared to time-only modulation analyses can also serve as a template for other theoretical models with different dark matter candidates, mediators and cosmology. For the $U(1)$ model with two Dirac fermions fitting the XENON1T excess and the experimental conditions of XENONnT, taking into account the annual variation of the signal rate and recoil energy allows for a faster and more precise determination of the free model parameters., Comment: 23 pages, 10 figures, 1 table

An analysis of a tower of hidden sectors coupled to each other, with one of these hidden sectors coupled to the visible sector, is given and the implications of such couplings on physics in the visible sector are investigated. Thus the analysis considers $n$ number of hidden sectors where the visible sector couples only to hidden sector 1, while the latter couples also to hidden sector 2, and the hidden sector 2 couples to hidden sector 3 and so on. A set of successively feeble couplings of the hidden sectors to the visible sector are generated in such a set up. In general each of these sectors live in a different heat bath. We develop a closed form set of coupled Boltzmann equations for the correlated evolution of the temperatures and number densities of each of the heat baths. We then apply the formalism to a simplified model with scalar portals between the different sectors. Predictions related to dark matter direct detection experiments and future CMB probes of dark radiation are made., Comment: 27 pages, 9 figures. Accepted for publication in JHEP

The search for particle-like dark matter with meV-to-GeV masses has developed rapidly in the past few years. We summarize the science case for these searches, the recent progress, and the exciting upcoming opportunities. Funding for Research and Development and a portfolio of small dark matter projects will allow the community to capitalize on the substantial recent advances in theory and experiment and probe vast regions of unexplored dark-matter parameter space in the coming decade., Comment: Contribution to Snowmass 2021. v2: includes endorsers and minor changes

In this paper we will list a few important goals that need to be addressed in the next decade, also taking into account the current discordances between the different cosmological probes, such as the disagreement in the value of the Hubble constant $H_0$, the $\sigma_8$--$S_8$ tension, and other less statistically significant anomalies. While these discordances can still be in part the result of systematic errors, their persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the necessity for new physics or generalisations beyond the standard model. In this paper, we focus on the $5.0\,\sigma$ tension between the {\it Planck} CMB estimate of the Hubble constant $H_0$ and the SH0ES collaboration measurements. After showing the $H_0$ evaluations made from different teams using different methods and geometric calibrations, we list a few interesting new physics models that could alleviate this tension and discuss how the next decade's experiments will be crucial. Moreover, we focus on the tension of the {\it Planck} CMB data with weak lensing measurements and redshift surveys, about the value of the matter energy density $\Omega_m$, and the amplitude or rate of the growth of structure ($\sigma_8,f\sigma_8$). We list a few interesting models proposed for alleviating this tension, and we discuss the importance of trying to fit a full array of data with a single model and not just one parameter at a time. Additionally, we present a wide range of other less discussed anomalies at a statistical significance level lower than the $H_0$--$S_8$ tensions which may also constitute hints towards new physics, and we discuss possible generic theoretical approaches that can collectively explain the non-standard nature of these signals.[Abridged], Comment: Contribution to Snowmass 2021. 224 pages, 27 figures. Accepted for publication in JHEAp

The recent analysis from the SH0ES Collaboration has confirmed the existence of a Hubble tension between measurements at high redshift ($z> 1000$) and at low redshift ($z<1$) at the $5\sigma$ level with the low redshift measurement giving a higher value. In this work we propose a particle physics model that can help alleviate the Hubble tension via an out-of-equilibrium hidden sector coupled to the visible sector. The particles that populate the dark sector consist of a dark fermion, which acts as dark matter, a dark photon, a massive scalar and a massless pseudo-scalar. Assuming no initial population of particles in the dark sector, feeble couplings between the visible and the hidden sectors via kinetic mixing populate the dark sector even though the number densities of hidden sector particles never reach their equilibrium distribution and the two sectors remain at different temperatures. A cosmologically consistent analysis is presented where a correlated evolution of the visible and the hidden sectors with coupled Boltzmann equations involving two temperatures, one for the visible sector and the other for the hidden sector, is carried out. The relic density of the dark matter constituted of dark fermions is computed in this two-temperature formalism. As a consequence, BBN predictions are upheld with a minimal contribution to $\Delta N_{\rm eff}$. However, the out-of-equilibrium decay of the massive scalar to the massless pseudo-scalar close to the recombination time causes an increase in $\Delta N_{\rm eff}$ that can help weaken the Hubble tension., Comment: 28 pages, 7 figures, 1 table (Accepted for publication in JCAP)

The recent muon $g-2$ result from Fermilab combined with the Brookhaven result, strongly points to new physics beyond the Standard Model which can be well described by the electroweak sector of supersymmetry if the masses of the sleptons and some of the electroweak gauginos are in the few hundred GeV range. However, the Higgs boson mass measurement at 125 GeV indicates a mass scale for squarks which lies in the few TeV region indicating a split mass spectrum between squarks and sleptons. This apparent puzzle is resolved in a natural way in gluino-driven radiative breaking of the electroweak symmetry where radiative breaking is driven by a large gluino mass and the gluino color interactions lead to a large splitting between the squarks and the sleptons. We show that an analysis without prejudice using an artificial neural network also leads to the gluino-driven radiative breaking. We use a set of benchmarks and a deep neural network analysis to test the model for the discovery of light sleptons and sneutrinos at HL-LHC and HE-LHC., Comment: 18 pages, 6 figures, 6 tables (conference proceedings, 10th ICNFP 2021, Crete, Greece). arXiv admin note: text overlap with arXiv:2107.06021

Analysis of EDGES data shows an absorption signal of the redshifted 21-cm line of atomic hydrogen at $z\sim 17$ which is stronger than expected from the standard $\Lambda$CDM model. The absorption signal interpreted as brightness temperature $T_{21}$ of the 21-cm line gives an amplitude of $-$500$_{-500}^{+200}$ mK at 99\% C.L. which is a 3.8$\sigma$ deviation from what the standard $\Lambda$CDM cosmology gives. We present a particle physics model for the baryon cooling where a fraction of the dark matter resides in the hidden sector with a $U(1)$ gauge symmetry and a Stueckelberg mechanism operates mixing the visible and the hidden sectors with the hidden sector consisting of dark Dirac fermions and dark photons. The Stueckelberg mass mixing mechanism automatically generates a millicharge for the hidden sector dark fermions providing a theoretical basis for using millicharged dark matter to produce the desired cooling of baryons seen by EDGES by scattering from millicharged dark matter. We compute the relic density of the millicharged dark matter by solving a set of coupled equations for the dark fermion and dark photon yields and for the temperature ratio of the hidden sector and the visible sector heat baths. For the analysis of baryon cooling, we analyze the evolution equations for the temperatures of baryons and millicharged dark matter as a function of the redshift. We exhibit regions of the parameter space which allow consistency with the EDGES data. We note that the Stueckelberg mechanism arises naturally in strings and the existence of a millicharge would point to its string origin., Comment: 32 pages, 6 figures, 1 table (Accepted for publication in JHEP)

We assess the future directions for the search for supersymmetry at the Large Hadron Collider in view of the new precision results on the muon anomaly by the Fermilab Collaboration. The existence of a deviation of size 4.1$\sigma$ from the Standard Model prediction points to light sleptons and light weakinos in the mass range of few hundred GeV while the observation of the Higgs boson mass at $\sim 125$ GeV points to squark masses lying in the few TeV range. Thus a split sparticle spectrum is indicated. We discuss the possibility of such a split sparticle spectrum in the supergravity unified model and show that a splitting of the sfermion spectrum into light sleptons and heavy squarks naturally arises within radiative breaking of the electroweak symmetry driven by heavy gluinos ($\tilde g$SUGRA). We discuss the possible avenues for the discovery of supersymmetry at the LHC within this framework under the further constraint of the recent muon anomaly result from the Fermilab Collaboration. We show that the most likely candidates for early discovery of a sparticle at the LHC are the chargino, the stau, the smuon and the selectron. We present a set of benchmarks and discuss future directions for further work. Specifically, we point to the most promising channels for SUSY discovery and estimate the integrated luminosity needed for the discovery of these benchmarks at the High Luminosity LHC and also at the High Energy LHC., Comment: Contribution to Snowmass

A variety of supergravity and string based models contain hidden sectors which can play a role in particle physics phenomena and in cosmology. In this note we discuss the possibility that the visible sector and the hidden sectors in general live in different heat baths. Further, it is entirely possible that dark matter resides partially or wholly in hidden sectors in the form of dark Dirac fermions, dark neutralinos or dark photons. A proper analysis of dark matter and of dark forces in this case requires that one deals with a multi-temperature universe. We discuss the basic formalism which includes the multi-temperature nature of visible and hidden sectors in the analysis of phenomena observable in the visible sectors. Specifically we discuss the application of the formalism for explaining the velocity dependence of dark matter cross sections as one extrapolates from galaxy scales to scales of galaxy clusters. Here the dark photon exchange among dark fermions can produce the desired velocity dependent cross sections consistent with existing galactic cross section data indicating the existence of a new fifth (dark) force. We also discuss the possibility that the dark photon may constitute a significant portion of dark matter. We demonstrate a realization of this possibility in a universe with two hidden sectors and with the visible sector and the hidden sectors in different heat baths which allows a satisfaction of the constraints that the dark photon have a lifetime larger than the age of the universe and that its relic density be consistent with Planck data. Future directions for further work are discussed., Comment: Contribution to Snowmass

We investigate the Yukawa coupling unification for the third generation in a class of $\mathsf{SO(10)}$ unified models which are consistent with the 4.2 $\sigma$ deviation from the standard model of the muon $g-2$ seen by the Fermilab experiment E989. A recent analysis in supergravity grand unified models shows that such an effect can arise from supersymmetric loops correction. Using a neural network, we further analyze regions of the parameter space where Yukawa coupling unification consistent with the Fermilab result can appear. In the analysis we take into account the contributions to Yukawas from the cubic and the quartic interactions. We test the model at the high luminosity and high energy LHC and estimate the integrated luminosities needed to discover sparticles predicted by the model., Comment: 26 pages, 5 figures, 9 tables

Using an artificial neutral network we explore the parameter space of supergravity grand unified models consistent with the combined Fermilab E989 and Brookhaven E821 data on $(g-2)_\mu$. The analysis indicates that the region favored by the data is the one generated by gluino-driven radiative breaking of the electroweak symmetry. This region naturally leads to a split sparticle spectrum with light sleptons and weakinos but heavy squarks, with the stau and the chargino as the lightest charged particles. We show that if the entire deviation from the standard model $(g-2)_{\mu}$ arises from supersymmetry, then supersymmetry is discoverable at HL-LHC and HE-LHC via production and decay of sleptons within the optimal integrated luminosity of HL-LHC and with a smaller integrated luminosity at HE-LHC., Comment: 15 pages, 12 figures, 8 tables. (Accepted for publication in PRD)

An analysis of sub-MeV dark photon as dark matter is given which is achieved with two hidden sectors, one of which interacts directly with the visible sector while the second has only indirect coupling with the visible sector. The formalism for the evolution of three bath temperatures for the visible sector and the two hidden sectors is developed and utilized in solution of Boltzmann equations coupling the three sectors. We present exclusion plots where the sub-MeV dark photon can be dark matter. The analysis can be extended to a multi-temperature universe with multiple hidden sectors and multiple heat baths., Comment: 33 pages, 7 figures, 3 tables -- Accepted in JHEP

It is shown that a decaying neutralino in a supergravity unified framework is a viable candidate for dark matter. Such a situation arises in the presence of a hidden sector with ultraweak couplings to the visible sector where the neutralino can decay into the hidden sector's lightest supersymmetric particle (LSP) with a lifetime larger than the lifetime of the universe. We present a concrete model where the MSSM/SUGRA is extended to include a hidden sector comprised of $U(1)_{X_1} \times U(1)_{X_2}$ gauge sector and the LSP of the hidden sector is a neutralino which is lighter than the LSP neutralino of the visible sector. We compute the loop suppressed radiative decay of the visible sector neutralino into the neutralino of the hidden sector and show that the decay can occur with a lifetime larger than the age of the universe. The decaying neutralino can be probed by indirect detection experiments, specifically by its signature decay into the hidden sector neutralino and an energetic gamma ray photon. Such a gamma ray can be searched for with improved sensitivity at Fermi-LAT and by future experiments such as the Square Kilometer Array (SKA) and the Cherenkov Telescope Array (CTA). We present several benchmarks which have a natural suppression of the hadronic channels from dark matter annihilation and decays and consistent with measurements of the antiproton background., Comment: 29 pages, 3 tables and 4 figures

We present a particle physics model to explain the observed enhancement in the Xenon-1T data at an electron recoil energy of 2.5 keV. The model is based on a $U(1)$ extension of the Standard Model where the dark sector consists of two essentially mass degenerate Dirac fermions in the sub-GeV region with a small mass splitting interacting with a dark photon. The dark photon is unstable and decays before the big bang nucleosynthesis, which leads to the dark matter constituted of two essentially mass degenerate Dirac fermions. The Xenon-1T excess is computed via the inelastic exothermic scattering of the heavier dark fermion from a bound electron in xenon to the lighter dark fermion producing the observed excess events in the recoil electron energy. The model can be tested with further data from Xenon-1T and in future experiments such as SuperCDMS., Comment: 21 pages, 4 figures, 1 table. Accepted for publication in JHEP

The short distance behavior of dark matter (DM) at galaxy scales exhibits several features not explained by the typical cold dark matter (CDM) with velocity-independent cross-section. We discuss a particle physics model with a hidden sector interacting feebly with the visible sector where a dark fermion self-interacts via a dark force with a light dark photon as the mediator. We study coupled Boltzmann equations involving two temperatures, one for each sector. We fit the velocity-dependent DM cross-section to the data from scales of dwarf galaxies to clusters consistent with relic density constraint., Comment: 11 pages, 9 figures, 1 table

We consider a class of unified models based on the gauge group $\mathsf{SO(10)}$ which with appropriate choice of Higgs representations generate in a natural way a pair of light Higgs doublets needed to accomplish electroweak symmetry breaking. In this class of models higher dimensional operators of the form matter-matter-Higgs-Higgs in the superpotential after spontaneous breaking of the GUT symmetry generate contributions to Yukawa couplings which are comparable to the ones from cubic interactions. Specifically we consider an $\mathsf{SO(10)}$ model with a sector consisting of $\mathsf{126+\overline{126} + 210}$ of heavy Higgs which breaks the GUT symmetry down to the standard model gauge group and a sector consisting of $2\times \mathsf{10+120}$ of light Higgs fields. In this model we compute the corrections from the quartic interactions to the Yukawa couplings for the top and the bottom quarks and for the tau lepton. It is then shown that inclusion of these corrections to the GUT scale Yukawas allows for consistency of the top, bottom and tau masses with experiment for low $\tan\beta$ with a value as low as $\tan\beta$ of 5$-$10. We compute the sparticle spectrum for a set of benchmarks and find that satisfaction of the relic density is achieved via a compressed spectrum and coannihilation and three sets of coannihilations appear: chargino-neutralino, stop-neutralino and stau-neutralino. We investigate the chargino-neutralino coannihilation in detail for the possibility of observation of the light chargino at the high luminosity LHC (HL-LHC) and at the high energy LHC (HE-LHC) which is a possible future 27 TeV hadron collider. It is shown that all benchmark models but one can be discovered at HL-LHC and all would be discoverable at HE-LHC. The ones discoverable at both machines require a much shorter time scale and a lower integrated luminosity at HE-LHC., Comment: 27 pages, 5 figures and 9 tables

SUSY/SUGRA models with naturalness defined via small $\mu$ are constrained due to experiment on the relic density and the experimental limits on the WIMP-proton cross-section and WIMP annihilation cross-section from indirect detection experiments. Specifically models with small $\mu$ where the neutralino is higgsino-like lead to dark matter relic density below the observed value. In several works this problem is overcome by assuming dark matter to be constituted of more than one component and the neutralino relic density deficit is made up from contributions from other components. In this work we propose that the dark matter consists of just one component, i.e., the lightest neutralino and the relic density of the higgsino-like neutralino receives contributions from the usual freeze-out mechanism along with contributions arising from the decay of hidden sector neutralinos. The model we propose is an extended MSSM model where the hidden sector is constituted of a $U(1)_X$ gauge sector along with matter charged under $U(1)_X$ which produce two neutralinos in the hidden sector. The $U(1)_X$ and the hypercharge $U(1)_Y$ of the MSSM have kinetic and Stueckelberg mass mixing where the mixings are ultraweak. In this case the hidden sector neutralinos have ultraweak interactions with the visible sector. Because of their ultraweak interactions the hidden sector neutralinos are not thermally produced and we assume their initial relic density to be negligible. However, they can be produced via interactions of MSSM particles in the early universe, and once produced they decay to the neutralino. For a range of mixings the decays occur before the BBN producing additional relic density for the neutralino. Models of this type are testable in dark matter direct and indirect detection experiments and at the high luminosity and high energy LHC., Comment: 31 pages, 8 figures

In extended supersymmetric models with a hidden sector the lightest $R$-parity odd particle can reside in the hidden sector and act as dark matter. We consider the case when the hidden sector has ultraweak interactions with the visible sector. An interesting phenomenon arises if the LSP of the visible sector is charged in which case it will decay to the hidden sector dark matter. Due to the ultraweak interactions, the LSP of the visible sector will be long-lived decaying outside the detector after leaving a track inside. We investigate this possibility in the framework of a $U(1)_X$-extended MSSM/SUGRA model with a small gauge kinetic mixing and mass mixing between the $U(1)_X$ and $U(1)_Y$ where $U(1)_Y$ is the gauge group of the hypercharge. Specifically we investigate the case when the LSP of MSSM is a stop which decays into the hidden sector dark matter and has a lifetime long enough to traverse the LHC detector without decay. It is shown that such a particle can be detected at the HL-LHC and HE-LHC as an $R$-hadron which will look like a slow moving muon with a large transverse momentum $p_T$ and so can be detected by the track it leaves in the inner tracker and in the muon spectrometer. Further, due to the ultraweak couplings between the hidden sector and the MSSM fields, the dark matter particle has a relic density arising from a combination of the freeze-out and freeze-in mechanisms. It is found that even for the ultraweak or feeble interactions the freeze-out contribution relative to freeze-in contribution to the relic density is substantial to dominant, varying between 30\% to 74\% for the model points considered. It is subdominant to freeze-in for relatively small stop masses with relatively larger stop annihilation cross-sections and the dominant contribution to the relic density for relatively large stop masses and relatively smaller stop annihilation cross-sections., Comment: 29 pages, 6 figures

The presence of a hidden sector with very weak interactions with the standard model has significant implications on LHC signatures. In this work we discuss LHC phenomenology with the inclusion of a hidden sector by a $U(1)$ extension of MSSM/SUGRA. We consider both kinetic mixing and Stueckelberg mass mixing between the $U(1)$ gauge field of the hidden sector and $U(1)_Y$ of the visible sector. Such a model has an extended parameter space. We consider here two limited regions of this parameter space. In the first case we consider a $U(1)$ gauge field along with chiral fields needed for the Stueckelberg mechanism to operate and discuss the mixing between the hidden and the visible sectors. Here if the stau is the lightest sparticle in the MSSM sector and the neutralino of the hidden sector is the LSP of the full system and a dark matter candidate, the stau can be long-lived and decay inside an LHC detector tracker. In the second case we include extra vectorlike matter in the hidden sector which can give rise to a Dirac fermion in addition to the two neutralinos in the hidden sector. The neutralino sector now has six neutralinos and we assume that the lightest of these is the LSP and is higgsino-like. In this case the dark matter is constituted of a Majorana and a Dirac fermion, and a small $\mu$ leads to heavy Higgs boson masses which reside in the observable range of HL-LHC and HE-LHC., Comment: Talks presented at the 2019 Meeting of the Division of Particles and Fields of the American Physical Society (DPF2019), July 29 - August 2, 2019, Northeastern University, Boston, C1907293

It is very likely that similar to the case of visible matter, dark matter too is composed of more than one stable component. In this work we investigate a two-component dark matter with one component from the visible sector and the other from the hidden sector. Specifically we consider a $U(1)_X$ hidden sector extension of MSSM/SUGRA where we allow for kinetic and Stueckelberg mass mixing between the two abelian $U(1)'s$, i.e., $U(1)_X$ and $U(1)_Y$. We further assume that the hidden sector has chiral matter which leads to a Dirac fermion as a candidate for dark matter. The lightest neutralino in the visible sector and the Dirac fermion in the hidden sector then constitute the two components of dark matter. We investigate in particular MSSM/SUGRA models with radiative breaking occurring on the hyperbolic branch where the Higgs mixing parameter $\mu$ is small (order the electroweak scale) which leads to a lightest neutralino being dominantly a higgsino. While dark matter constituted only of higgsinos is significantly constrained by data on dark matter relic density and by limits on spin independent proton-DM scattering cross section, consistency with data can be achieved if only a fraction of the dark matter relic density is constituted of higgsinos with the rest coming from the hidden sector. An aspect of the proposed model is the prediction of a relatively light CP odd Higgs $A$ (as well as a CP even $H$ and a charged Higgs $H^{\pm}$) which is observable at HL-LHC and HE-LHC. We perform a detailed collider analysis search for the CP odd Higgs using boosted decision trees in $\tau_h\tau_h$ final states and compare the discovery potential at HL-LHC and HE-LHC. We show that while several of the points among our benchmarks may be observable at HL-LHC, all of them are visible at HE-LHC with much lower integrated luminosities thus reducing significantly the run time for discovery., Comment: 31 pages, 6 figures

We investigate a class of models where the supergravity model with the standard model gauge group is extended by a hidden sector $U(1)_X$ gauge group and where the lightest supersymmetric particle is the neutralino in the hidden sector. We investigate this possibility in a class of models where the stau is the lightest supersymmetric particle in the MSSM sector and the next-to-lightest supersymmetric particle of the $U(1)_X$-extended SUGRA model. In this case the stau will decay into the neutralino of the hidden sector. For the case when the mass gap between the stau and the hidden sector neutralino is small and the mixing between the $U(1)_Y$ and $U(1)_X$ is also small, the stau can decay into the hidden sector neutralino and a tau which may be reconstructed as a displaced track coming from a high $p_T$ track of the charged stau. Simulations for this possibility are carried out for HL-LHC and HE-LHC. The discovery of such a displaced track from a stau will indicate the presence of hidden sector dark matter., Comment: 27 pages, 5 figures (Accepted for publication in PRD)

The discovery of the Higgs boson in 2012, by the ATLAS and CMS experiments, was a success achieved with only a percent of the entire dataset foreseen for the LHC. It opened a landscape of possibilities in the study of Higgs boson properties, Electroweak Symmetry breaking and the Standard Model in general, as well as new avenues in probing new physics beyond the Standard Model. Six years after the discovery, with a conspicuously larger dataset collected during LHC Run 2 at a 13 TeV centre-of-mass energy, the theory and experimental particle physics communities have started a meticulous exploration of the potential for precision measurements of its properties. This includes studies of Higgs boson production and decays processes, the search for rare decays and production modes, high energy observables, and searches for an extended electroweak symmetry breaking sector. This report summarises the potential reach and opportunities in Higgs physics during the High Luminosity phase of the LHC, with an expected dataset of pp collisions at 14 TeV, corresponding to an integrated luminosity of 3 ab$^{-1}$. These studies are performed in light of the most recent analyses from LHC collaborations and the latest theoretical developments. The potential of an LHC upgrade, colliding protons at a centre-of-mass energy of 27 TeV and producing a dataset corresponding to an integrated luminosity of 15 ab$^{-1}$, is also discussed., Comment: Report from Working Group 2 on the Physics of the HL-LHC, and Perspectives at the HE-LHC, 364 pages

This is the third out of five chapters of the final report [1] of the Workshop on Physics at HL-LHC, and perspectives on HE-LHC [2]. It is devoted to the study of the potential, in the search for Beyond the Standard Model (BSM) physics, of the High Luminosity (HL) phase of the LHC, defined as $3~\mathrm{ab}^{-1}$ of data taken at a centre-of-mass energy of $14~\mathrm{TeV}$, and of a possible future upgrade, the High Energy (HE) LHC, defined as $15~\mathrm{ab}^{-1}$ of data at a centre-of-mass energy of $27~\mathrm{TeV}$. We consider a large variety of new physics models, both in a simplified model fashion and in a more model-dependent one. A long list of contributions from the theory and experimental (ATLAS, CMS, LHCb) communities have been collected and merged together to give a complete, wide, and consistent view of future prospects for BSM physics at the considered colliders. On top of the usual standard candles, such as supersymmetric simplified models and resonances, considered for the evaluation of future collider potentials, this report contains results on dark matter and dark sectors, long lived particles, leptoquarks, sterile neutrinos, axion-like particles, heavy scalars, vector-like quarks, and more. Particular attention is placed, especially in the study of the HL-LHC prospects, to the detector upgrades, the assessment of the future systematic uncertainties, and new experimental techniques. The general conclusion is that the HL-LHC, on top of allowing to extend the present LHC mass and coupling reach by $20-50\%$ on most new physics scenarios, will also be able to constrain, and potentially discover, new physics that is presently unconstrained. Moreover, compared to the HL-LHC, the reach in most observables will generally more than double at the HE-LHC, which may represent a good candidate future facility for a final test of TeV-scale new physics., Comment: Report from Working Group 3 on the Physics of the HL-LHC, and Perspectives at the HE-LHC; v2: final version updated with the latest contributions and summaries; 239 pages + refs; v3: typos and character misprint in Fig. 7.2 fixed; v4: added one missing author

One of the early criterion proposed for naturalness was a relatively small Higgs mixing parameter $\mu$ with $\mu/M_Z$ order few. A relatively small $\mu$ may lead to heavier Higgs masses ($H^0, A, H^{\pm}$ in MSSM) which are significantly lighter than other scalars such as squarks. Such a situation is realized on the hyperbolic branch of radiative breaking of the electroweak symmetry. In this analysis we construct supergravity unified models with relatively small $\mu$ in the sense described above and discuss the search for the charged Higgs boson $H^{\pm}$ at HL-LHC and HE-LHC where we also carry out a relative comparison of the discovery potential of the two using the decay channel $H^{\pm} \to \tau \nu$. It is shown that an analysis based on the traditional linear cuts on signals and backgrounds is not very successful in extracting the signal while, in contrast, machine learning techniques such as boosted decision trees prove to be far more effective. Thus it is shown that models not discoverable with the conventional cut analyses become discoverable with machine learning techniques. Using boosted decision trees we consider several benchmarks and analyze the potential for their $5\sigma$ discovery at the 14 TeV HL-LHC and at 27 TeV HE-LHC. It is shown that while the ten benchmarks considered with the charged Higgs boson mass in the range 373 GeV- 812 GeV are all discoverable at HE-LHC, only four of the ten with Higgs boson masses in the range 373 GeV-470 GeV are discoverable at HL-LHC. Further, while the model points discoverable at both HE-LHC and HL-LHC would require up to 7 years of running time at HL-LHC, they could all be discovered in a period of few months at HE-LHC., Comment: 33 pages, six figures (Accepted for publication in PRD)

A correlated analysis of observables arising from loop induced effects from a vectorlike generation is given. The observables include flavor changing radiative decays $\mu\to e \gamma, \tau\to \mu \gamma, \tau\to e \gamma$, electric dipole moments of the charged leptons $e,\mu, \tau$, and corrections to magnetic dipole moments of $g_\mu-2$ and $g_e-2$. In this work we give a full analysis of the corrections to these observables by taking into account both the supersymmetry loops as well as the exchange of a vectorlike leptonic generation. Thus the fermion mass matrix involves a $5\times 5$ mixing matrix while the scalar sector involves a $10\times 10$ mixing matrix including the CP violating phases from the vectorlike sector. The analysis is done under the constraint of the Higgs boson mass at the experimentally measured value. The loops considered include the exchange of $W$ and $Z$ bosons and of leptons and a mirror lepton, and the exchange of charginos and neutralinos, sleptons and mirror sleptons. The correction to the diphoton decay of the Higgs $h\to \gamma\gamma$ including the exchange of the vectorlike leptonic multiplet is also computed., Comment: 34 pages, 8 figures (Accepted for publication in PRD)

The discovery of the Higgs boson at $\sim 125$ GeV indicates that the scale of weak scale supersymmetry is higher than what was perceived in the pre-Higgs boson discovery era and lies in the several TeV region. This makes the discovery of supersymmetry more challenging and argues for hadron colliders beyond LHC at $\sqrt s=14$ TeV. The Future Circular Collider (FCC) study at CERN is considering a 100 TeV collider to be installed in a 100 km tunnel in the Lake Geneva basin. Another 100 km collider being considered in China is the Super proton-proton Collider (SppC). A third possibility recently proposed is the High-Energy LHC (HE-LHC) which would use the existing CERN tunnel but achieve a center-of-mass energy of 28 TeV by using FCC magnet technology at significantly higher luminosity than at the High Luminosity LHC (HL-LHC). In this work we investigate the potential of HE-LHC for the discovery of supersymmetry. We study a class of supergravity unified models under the Higgs boson mass and the dark matter relic density constraints and compare the analysis with the potential reach of the HL-LHC. A set of benchmarks are presented which are beyond the discovery potential of HL-LHC but are discoverable at HE-LHC. For comparison, we study model points at HE-LHC which are also discoverable at HL-LHC. For these model points, it is found that their discovery would require a HL-LHC run between 5-8 years while the same parameter points can be discovered in a period of few weeks to $\sim 1.5$ yr at HE-LHC running at its optimal luminosity of $2.5\times 10^{35}$ cm$^{-2}$ s$^{-1}$. The analysis indicates that the HE-LHC possibility should be seriously pursued as it would significantly increase the discovery reach for supersymmetry beyond that of HL-LHC and decrease the run period for discovery., Comment: 29 pages, 7 figures Accepted for publication in PRD

We investigate the possibility of testing supergravity unified models with scalar masses in the range 50-100 TeV and much lighter gaugino masses at the Large Hadron Collider. The analysis is carried out under the constraints that models produce the Higgs boson mass consistent with experiment and also produce dark matter consistent with WMAP and PLANCK experiments. A set of benchmarks in the supergravity parameter space are investigated using a combination of signal regions which are optimized for the model set. It is found that some of the models with scalar masses in the 50-100 TeV mass range are discoverable with as little as 100 fb$^{-1}$ of integrated luminosity and should be accessible at the LHC RUN II. The remaining benchmark models are found to be discoverable with less than 1000 fb$^{-1}$ of integrated luminosity and thus testable in the high luminosity era of the LHC, i.e., at HL-LHC. It is shown that scalar masses in the 50-100 TeV range but gaugino masses much lower in mass produce unification of gauge coupling constants, consistent with experimental data at low scale, with as good an accuracy (and sometimes even better) as models with low ($\mathcal{O}(1)$ TeV) weak scale supersymmetry. Decay of the gravitinos for the supergravity model benchmarks are investigated and it is shown that they decay before the Big Bang Nucleosynthesis (BBN). Further, we investigate the non-thermal production of neutralinos from gravitino decay and it is found that the non-thermal contribution to the dark matter relic density is negligible relative to that from the thermal production of neutralinos for reheat temperature after inflation up to $10^9$ GeV. An analysis of the direct detection of dark matter for SUGRA models with high scalar masses is also discussed., Comment: 34 pages, 10 figures. arXiv admin note: text overlap with arXiv:1704.04669

The lack of observation of supersymmetry thus far implies that the weak supersymmetry scale is larger than what was thought before the LHC era. This observation is strengthened by the Higgs boson mass measurement at $\sim 125$ GeV which within supersymmetric models implies a large loop correction and a weak supersymmetry scale lying in the several TeV region. In addition if neutralino is the dark matter, its relic density puts further constraints on models often requiring coannihilation to reduce the neutralino relic density to be consistent with experimental observation. The coannihilation in turn implies that the mass gap between the LSP and the NLSP will be small leading to softer final states and making the observation of supersymmetry challenging. In this work we investigate stau coannihilation models within supergravity grand unified models and the potential of discovery of such models at the LHC in the post Higgs boson discovery era. We utilize a variety of signal regions to optimize the discovery of supersymmetry in the stau coannihilation region. In the analysis presented we impose the relic density constraint as well as the constraint of the Higgs boson mass. The range of sparticle masses discoverable up to the optimal integrated luminosity of the HL-LHC is investigated. It is found that the mass difference between the stau and the neutralino does not exceed $\sim 20$ GeV over the entire mass range of the models explored. Thus the discovery of a supersymmetric signal arising from the stau coannihilation region will also provide a measurement of the neutralino mass. The direct detection of neutralino dark matter is analyzed within the class of stau coannihilation models investigated. The analysis is extended to include multi-particle coannihilation where stau along with chargino and the second neutralino enter in the stau coannihilation process., Comment: 32 pages, 12 figures

Higgs boson mass measurement at $\sim 125$ GeV points to a high scale for SUSY specifically the scalar masses. If all the scalars are heavy, supersymmetric contribution to the leptonic $g-2$ moments will be significantly reduced. On the other hand the Brookhaven experiment indicates a 3sigma deviation from the standard model prediction. Here we analyze the leptonic $g-2$ moments in an extended MSSM model with inclusion of a vector like leptonic generation which brings in new sources of CP violation. In this work we consider the contributions to the leptonic $g-2$ moments arising from the exchange of charginos and neutralinos, sleptons and mirror sleptons, and from the exchange of $W$ and $Z$ bosons and of leptons and mirror leptons. We focus specifically on the $g-2$ moments for the muon and the electron where sensitive measurements exist. Here it is shown that one can get consistency with the current data on $g-2$ under the Higgs boson mass constraint. Dependence of the moments on CP phases from the extended sector are analyzed and it is shown that they are sensitively dependent on the phases from the new sector. It is shown that the corrections to the leptonic moments arising from the extended MSSM sector will be non-vanishing even if the SUSY scale extends into the PeV region., Comment: 19 pages, 7 figures

An analysis is given of the chromoelectric dipole moment of quarks and of the neutron in an MSSM extension where the matter sector contains an extra vectorlike generation of quarks and mirror quarks. The analysis includes contributions to the CEDM from the exchange of the $W$ and the $Z$ bosons, from the exchange of charginos and neutralinos and the gluino. Their contribution to the EDM of quarks is investigated. The interference between the MSSM sector and the new sector with vectorlike quarks is investigated. It is shown that inclusion of the vectorlike quarks can modify the quark EDMs in a significant way. Further, this interference also provides a probe of the vectorlike quark sector. These results are of interest as in the future measurements on the neutron EDM could see an improvement up to two orders of magnitude over the current experimental limits and provide a window to new physics beyond the standard model., Comment: 37 pages, 3 tables, 11 figures. arXiv admin note: text overlap with arXiv:1503.06850. Accepted for publication in Physical Review D

The experimental limit on the neutron electric dipole moment is used as a possible probe of new physics beyond the standard model. Within MSSM we use the current experimental limit on the neutron EDM and possible future improvement as a probe of high scale SUSY. Quantitative analyses show that scalar masses as large as a PeV and larger could be probed in improved experiment far above the scales accessible at future colliders. We also discuss the neutron EDM as a probe of new physics models beyond MSSM. Specifically we consider an MSSM extension with a particle content including a vectorlike multiplet. Such an extension brings in new sources of CP violation beyond those in MSSM. These CP phases contribute to the EDM of the quarks and to the neutron EDM. These contributions are analyzed in this work where we include the supersymmetric loop diagrams involving the neutralinos, charginos, the gluino, squark and mirror squark exchange diagrams at the one loop level. We also take into account the contributions from the $W$, $Z$, quark and mirror quark exchanges arising from the mixings of the vectorlike generation with the three generations. It is shown that the experimental limit on the neutron EDM can be used to probe such new physics models. In the future one expects the neutron EDM to improve an order of magnitude or more allowing one to extend the probe of high scale SUSY and of new physics models. For the MSSM the probe of high scales could go up to and beyond PeV scale masses., Comment: 26 pages, 8 figures, 2 tables. Accepted for publication in PRD

The anomalous magnetic moment of the electron is determined experimentally with an accuracy of $2.8\times 10^{-13}$ and the uncertainty may decrease by an order of magnitude in the future. While the current data is in excellent agreement with the standard model, the possible future improvement in the error in $\Delta a_e= a_e^{\text{exp}}- a_e^{\text{theory}}$ has recently drawn interest in the electron anomalous magnetic moment as a possible probe of new physics beyond the standard model. In this work we give an analysis of such physics in an extension of the minimal supersymmetric standard model with a vector multiplet. In the extended model the electroweak contribution to the anomalous magnetic moment of the electron include loop diagrams involving in addition to the exchange of W and Z, the exchange of charginos, sneutrinos and mirror sneutrinos, and the exchange of neutralinos, sleptons and mirror sleptons. The analysis shows that a contribution to the electron magnetic moment much larger than expected by $m_e^2/m_\mu^2$ scaling of the deviation of the muon anomalous magnetic moment over the standard model prediction, i.e., $\Delta a_\mu = 3 \times 10^{-9}$ as given by the Brookhaven experiment, can be gotten within the MSSM extension. Effects of CP violating phases in the extended MSSM model on the corrections to the supersymmetric electroweak contributions to $a_e$ are also investigated. The analysis points to the possibility of detection of new physics effects with modest improvement on the error in $\Delta a_e= a_e^{\text{exp}} - a_e^{\text{theory}}$., Comment: 28 pages, 8 figures. Accepted for publication in Physical Review D. arXiv admin note: text overlap with arXiv:1312.2505

An analysis of the Dirac neutrino magnetic moment with standard model interactions gives $\mu_\nu\sim 3 \times 10^{-19} \mu_B (m_\nu/1 eV)$. The observation of a significantly larger magnetic moment will provide a clear signal of new physics beyond the standard model. The current experimental limits on the neutrino magnetic moments are orders of magnitude larger than the prediction with the standard model interactions and thus its test appears out of reach. Here we give an analysis of the Dirac neutrino magnetic moments within the framework of a minimal supersymmetric standard model extension with a vectorlike lepton generation. Specifically we compute the moments arising from the exchange of W and the charged leptons in the loop, as well as from the exchange of charginos, charged sleptons and charged mirror sleptons. It is shown that the neutrino moment in this case can be several orders of magnitude larger than the one with standard model like interactions, lying close to and below the current experimental upper limits and should be accessible in improved future experiment. A correlated prediction of the heaviest neutrino lifetimes from radiative decays to the lighter neutrinos via exchange of charginos and sleptons in the loops is also made. The predicted lifetimes are several orders of magnitudes smaller than the one with the standard model interactions and also lie close to the current experimental limits from analyses using the cosmic background neutrino data., Comment: 23 pages, 8 figures. arXiv admin note: text overlap with arXiv:1306.2275. Accepted for publication in PRD

An analysis of radiative decays of the neutrinos $\nu_j\to \nu_l \gamma$ is discussed in MSSM extensions with a vector like lepton generation. Specifically we compute neutrino decays arising from the exchange of charginos and charged sleptons where the photon is emitted by the charged particle in the loop. It is shown that while the lifetime of the neutrino decay in the Standard Model is $\sim 10^{43}$ yrs for a neutrino mass of 50 meV, the current lower limit from experiment from the analysis of the Cosmic Infrared Background is $\sim 10^{12}$ yrs and thus beyond the reach of experiment in the foreseeable future. However, in the extensions with a vector like lepton generation the lifetime for the decays can be as low as $\sim 10^{12}- 10^{14}$ yrs and thus within reach of future improved experiments. The effect of CP phases on the neutrino lifetime is also analyzed. It is shown that while both the magnetic and the electric transition dipole moments contribute to the neutrino lifetime, often the electric dipole moment dominates even for moderate size CP phases., Comment: 21 pages, 6 figures (Accepted for publication in Physical Review D)