arXiv subjects

Jason Kumar

Publications and source records attributed to Jason Kumar.

At least 55 records · Page 3Linked to original sources

arXiv2021

Low-mass inelastic dark matter direct detection via the Migdal effect

We consider searches for the inelastic scattering of low-mass dark matter at direct detection experiments, using the Migdal effect. We find that there are degeneracies between the dark matter mass and the mass splitting that are difficult to break. Using XENON1T data we set bounds on a previously unexplored region of the inelastic dark matter parameter space. For the case of exothermic scattering, we find that the Migdal effect allows xenon-based detectors to have sensitivity to dark matter with ${\cal O}(\mathrm{MeV})$ mass, far beyond what can be obtained with nuclear recoils alone.

hep-ph↗

arXiv2021

Prospects for measuring dark matter microphysics with observations of dwarf spheroidal galaxies

Dark matter annihilation in dwarf spheroidal (dSph) galaxies near the Milky Way has the potential to produce a detectable signature in gamma-rays. The amplitude of this signal depends on the dark matter density in a dSph, the dark matter particle mass, the number of photons produced in an annihilation, and the possibly velocity-dependent dark matter annihilation cross section. We argue that if the amplitude of the annihilation signal from multiple dSphs can be measured, it is possible to determine the velocity-dependence of the annihilation cross section. However, we show that doing so will require improved constraints on the dSph density profiles, including control of possible sources of systematic uncertainty. Making reasonable assumptions about future improvements, we make forecasts for the ability of current and future experiments -- including Fermi, CTA and AMEGO -- to constrain the dark matter annihilation velocity dependence.

astro-ph.CO↗

arXiv2021

MSSM dark matter and a light slepton sector: The Incredible Bulk

Recent experimental results from the LHC have placed strong constraints on the masses of QCD-charged superpartners. The MSSM parameter space is also constrained by the measurement of the Higgs boson mass, and the requirement that the relic density of lightest neutralinos be consistent with observations. Although large regions of the MSSM parameter space can be excluded by these combined bounds, leptophilic versions of the MSSM can survive these constraints. In this paper we consider a scenario in which the requirements of minimal flavor violation, vanishing $CP$-violation, and mass universality are relaxed, specifically focusing on scenarios with light sleptons. We find a large region of parameter space, analogous to the original bulk region, for which the lightest neutralino is a thermal relic with an abundance consistent with that of dark matter. We find that these leptophilic models are constrained by measurements of the magnetic and electric dipole moments of the electron and muon, and that these models have interesting signatures at a variety of indirect detection experiments.

hep-ph↗

arXiv2021

Comments on Brane Recombination, Finite Flux Vacua, and the Swampland

The Swampland program relies heavily on the conjecture that there can only be a finite number of flux vacua (FFV conjecture). Stipulating this FFV conjecture and applying it to some older work in flux vacua construction we show that within a patch of the landscape the FFV conjecture makes predictions on the non-existence of otherwise viable non-perturbative objects arising from brane recombination. Future gains in direct non-perturbative analysis could therefore not only test this prediction but also test portions of the Swampland program itself. We also discuss implications of a weaker FFV conjecture on the counting of flux vacua which predicts positivity of the brane central charge if the EFT analysis is to be qualitatively trusted.

hep-th↗

arXiv2020

Explaining the XENON1T excess with Luminous Dark Matter

We show that the excess in electron recoil events seen by the XENON1T experiment can be explained by relatively low-mass Luminous Dark Matter candidate. The dark matter scatters inelastically in the detector (or the surrounding rock), to produce a heavier dark state with a ~2.75 keV mass splitting. This heavier state then decays within the detector, producing a peak in the electron recoil spectrum which is a good fit to the observed excess. We comment on the ability of future direct detection datasets to differentiate this model from other Beyond the Standard Model scenarios, and from possible tritium backgrounds, including the use of diurnal modulation, multi-channel signals etc.,~as possible distinguishing features of this scenario.

hep-ph↗

arXiv2020

Effective $J$-factors for Milky Way dwarf spheroidal galaxies with velocity-dependent annihilation

We calculate the effective $J$-factors, which determine the strength of indirect detection signals from dark matter annihilation, for 25 dwarf spheroidal galaxies (dSphs). We consider several well-motivated assumptions for the relative velocity dependence of the dark matter annihilation cross section: $σ_A v$: $s$-wave (velocity independent), $p$-wave ($σ_A v \propto v^2$), $d$-wave ($σ_A v \propto v^4$), and Sommerfeld-enhancement in the Coulomb limit ($σ_A v \propto 1/v$). As a result we provide the largest and most updated sample of J-factors for velocity-dependent annihilation models. For each scenario, we use Fermi-LAT gamma-ray data to constrain the annihilation cross section. Due to the assumptions made in our gamma-ray data analysis, our bounds are comparable to previous bounds on both the $p$-wave and Sommerfeld-enhanced cross sections using dSphs. Our bounds on the $d$-wave cross section are the first such bounds using indirect detection data.

astro-ph.CO↗

arXiv2020

Contributions to $ΔN_{eff}$ from the dark photon of $U(1)_{T3R}$

We consider the effect on early Universe cosmology of the dark photon associated with the gauging of $U(1)_{T3R}$, a symmetry group under which only right-handed Standard Model fermions transform non-trivially. We find that cosmological constraints on this scenario are qualitatively much more severe than on other well-studied cases of a new $U(1)$ gauge group, because the dark photon couples to chiral fermions. In particular, the dark photon of $U(1)_{T3R}$ is always produced and equilibrates in the early Universe, no matter how small the gauge coupling, unless the symmetry-breaking scale is extremely large. This occurs because, no matter how the weak the coupling, the Goldstone mode (equivalently, the longitudinal polarization) does not decouple. As a result, even the limit of an extremely light and weakly-coupled dark photon of $U(1)_{T3R}$ is effectively ruled out by cosmological constraints, unless the symmetry-breaking scale is extremely large. We also discuss the possibility of ameliorating Hubble tension in this model.

hep-ph↗

arXiv2019

Dark matter astrometry at underground detectors with multiscatter events

We show that current and imminent underground detectors are capable of precision astrometry of dark matter. First we show that galactic dark matter velocity distributions can be obtained from reconstructed tracks of dark matter scattering on multiple nuclei during transit; using the liquid scintillator neutrino detector SNO+ as an example, we find that the dark matter velocity vector can be reconstructed event-by-event with such a small uncertainty, that the precision of dark matter astrometry will be limited mainly by statistics. We then determine the number of dark matter events required to determine the dispersion speed, escape speed, and velocity anisotropies of the local dark matter halo, and also find that with as few as $\mathcal{O}(10)$ events, dark matter signals may be discriminated from potential backgrounds arising as power-law distributions. Finally, we discuss the prospects of dark matter astrometry at other liquid scintillator detectors, dark matter experiments, and the recently proposed MATHUSLA detector.

hep-ph↗

arXiv2019

A sub-GeV dark matter model

We propose an extension of the Standard Model gauge symmetry by the gauge group $U(1)_{T3R}$ in order to address the Yukawa coupling hierarchy between the third generation fermions and the first two generation fermions of the SM. We assume that only the right-handed fermions of the first two generations are charged under the $U(1)_{T3R}$. In addition to the new dark gauge boson, we have a dark scalar particle whose vacuum expectation value (vev) breaks the $U(1)_{T3R}$ symmetry down to $Z_2$ symmetry and also explains the hierarchy problem. A vev of $\cal O$(GeV) is required to explain the mass parameters of the light flavor sector naturally. The dark matter (DM) particle arising from the model naturally has mass in the $\mathcal {O}$(1-100) MeV range. The model satisfies all the current constraints. We discuss the various prospects of the direct detection of the dark matter. We get both elastic and inelastic spin independent DM-nucleon scattering. The dark matter obtains the correct thermal relic density by annihilation.

hep-ph↗

arXiv2019

The Effective J-Factor of the Galactic Center for Velocity-Dependent Dark Matter Annihilation

We present the effective $J$-factors for the Milky Way for scenarios in which dark matter annihilation is p-wave or d-wave suppressed. We find that the velocity suppression of dark matter annihilation can have a sizable effect on the morphology of a potential dark matter annihilation signal in the Galactic Center. The gamma-ray flux from the innermost region of the Galactic Center is in particular suppressed. We find that for dark matter density profiles with steep inner slopes, the morphology of the Inner Galaxy gamma-ray emission in p-wave models can be made similar to the morphology in standard s-wave models. This similarity may suggest that model discrimination between s-wave and p-wave is challenging, for example, when fitting the Galactic Center excess. However, we show that it is difficult to simultaneously match s- and p-wave morphologies at both large and small angular scales. The $J$-factors we calculate may be implemented with astrophysical foreground models to self-consistently determine the morphology of the excess with velocity-suppressed dark matter annihilation.

astro-ph.HE↗

arXiv2019

Angular distribution of gamma-ray emission from velocity-dependent dark matter annihilation in subhalos

We consider the effect of velocity-dependent dark matter annihilation on the angular distribution of gamma rays produced in dark matter subhalos. We assume that the dark matter potential is spherically symmetric, characterized by a scale radius and scale density, and the velocity distribution is isotropic. We find that the effect of velocity-dependent dark matter annihilation is largely determined by dimensional analysis; the angular size of gamma-ray emission from an individual subhalo is rescaled by a factor which depends on the form of the dark matter distribution, but not on the halo parameters, while the relative normalization of the gamma-ray flux from different mass subhalos is rescaled by a factor which depends on the halo parameters, but not on the form of the dark matter distribution. We apply our results to a Navarro-Frenk-White profile for the case of an individual subhalo and comment on the application of these results to a distribution of subhalos.

astro-ph.CO↗

arXiv2019

Neutrino Topology Reconstruction at DUNE and Applications to Searches for Dark Matter Annihilation in the Sun

We consider a new technique for neutrino energy and topology reconstruction at DUNE. In particular, we show that when the direction of the incoming neutrino is known, one can use the measured directions of the outgoing leptonic and hadronic particles to reconstruct poorly-measured quantities, such as the hadronic cascade energy. We show that this alternative technique yields an energy resolution which is comparable to current reconstruction methods which sum measured energies. As a proof of concept we apply this new reconstruction method to a search for dark matter annihilation in the Sun. We show that the use of directional information from both the leptonic and hadronic interaction products allows one to effectively reject backgrounds and isolate the signal, giving competitive sensitivities.

astro-ph.HE↗

arXiv2019

Foraging for dark matter in large volume liquid scintillator neutrino detectors with multiscatter events

We show that dark matter with a per-nucleon scattering cross section $\gtrsim 10^{-28}~{\rm cm^2}$ could be discovered by liquid scintillator neutrino detectors like BOREXINO, SNO+, and JUNO. Due to the large dark matter fluxes admitted, these detectors could find dark matter with masses up to $10^{21}$ GeV, surpassing the mass sensitivity of current direct detection experiments (such as XENON1T and PICO) by over two orders of magnitude. We derive the spin-independent and spin-dependent cross section sensitivity of these detectors using existing selection triggers, and propose an improved trigger program that enhances this sensitivity by two orders of magnitude. We interpret these sensitivities in terms of three dark matter scenarios: (1) effective contact operators for scattering, (2) QCD-charged dark matter, and (3) a recently proposed model of Planck-mass baryon-charged dark matter. We calculate the flux attenuation of dark matter at these detectors due to the earth overburden, taking into account the earth's density profile and elemental composition, and nuclear spins.

hep-ph↗

arXiv2019

Dark Matter Through the Quark Vector Current Portal

We consider models of light dark matter coupled to quarks through a vector current interaction. For low energies, these models must be treated through the effective couplings to mesons, which are implemented here through the chiral Lagrangian. We find the rates of dark matter annihilation and decay to the light mesons, and find the expected photon spectrum from the decay of the hadrons. We compare to current and future observations, and show that there is a significant discovery reach for these models.

hep-ph↗

arXiv2019

Cosmological Constraints on Unstable Particles: Numerical Bounds and Analytic Approximations

Many extensions of the Standard Model predict large numbers of additional unstable particles whose decays in the early universe are tightly constrained by observational data. For example, the decays of such particles can alter the ratios of light-element abundances, give rise to distortions in the cosmic microwave background, alter the ionization history of the universe, and contribute to the diffuse photon flux. Constraints on new physics from such considerations are typically derived for a single unstable particle species with a single well-defined mass and characteristic lifetime. In this paper, by contrast, we investigate the cosmological constraints on theories involving entire ensembles of decaying particles --- ensembles which span potentially broad ranges of masses and lifetimes. In addition to providing a detailed numerical analysis of these constraints, we also formulate a set of simple analytic approximations for these constraints which may be applied to generic ensembles of unstable particles which decay into electromagnetically-interacting final states. We then illustrate how these analytic approximations can be used to constrain a variety of toy scenarios for physics beyond the Standard Model. For ease of reference, we also compile our results in the form of a table which can be consulted independently of the rest of the paper. It is thus our hope that this work might serve as a useful reference for future model-builders concerned with cosmological constraints on decaying particles, regardless of the particular model under study.

hep-ph↗

arXiv2018

Indirect Detection of Sub-GeV Dark Matter Coupling to Quarks

We consider photon signals arising from the annihilation or decay of low-mass (sub-GeV) dark matter which couples dominantly to quarks. In this scenario, the branching fractions to the various kinematically accessible hadronic final states can largely be determined from chiral perturbation theory. Several of these final states yield striking spectral features in the sub-GeV photon spectrum. New experiments, such as e-ASTROGAM and AMEGO, are in development to improve sensitivity in this energy range, and we discuss their potential sensitivity to this class of models.

hep-ph↗

arXiv2018

Searching for light from a dark matter clump

The DAMPE experiment has recently reported an electron spectrum that can be explained by dark matter annihilation into charged lepton pairs in a nearby dark matter clump. The accompanying bremsstrahlung may yield a gamma-ray excess with a known spectral shape that extends over an angular scale of $O(10^\circ)$. We show that such an excess is not present in Fermi-LAT data.

astro-ph.HE↗

arXiv2018

On the Prospects for Detecting a Net Photon Circular Polarization Produced by Decaying Dark Matter

If dark matter interactions with Standard Model particles are $CP$-violating, then dark matter annihilation/decay can produce photons with a net circular polarization. We consider the prospects for experimentally detecting evidence for such a circular polarization. We identify optimal models for dark matter interactions with the Standard Model, from the point of view of detectability of the net polarization, for the case of either symmetric or asymmetric dark matter. We find that, for symmetric dark matter, evidence for net polarization could be found by a search of the Galactic Center by an instrument sensitive to circular polarization with an efficiency-weighted exposure of at least $50000~\text{cm}^2~\text{yr}$, provided the systematic detector uncertainties are constrained at the $1\%$ level. Better sensitivity can be obtained in the case of asymmetric dark matter. We discuss the prospects for achieving the needed level of performance using possible detector technologies.

astro-ph.CO↗