A 130 GeV Gamma Ray Signal from Supersymmetry

The viability of neutralino dark matter as an explanation of the 130 GeV gamma ray signal from the Galactic Center recently observed by the Fermi Large Area Telescope is examined. It is found that the signal can be compatible with a sharp feature from internal bremsstrahlung from a mostly bino dark matter particle of mass around 145 GeV, augmented by a contribution from annihilation into gamma+Z via a small wino admixture. This scenario circumvents the problematic overproduction of lower energy continuum photons that plague line interpretations of this signal. Sleptons approximately degenerate in mass with the neutralino are required to enhance the internal bremsstrahlung feature.Comment: 16 pages, 2 figures. Fit to Fermi data updated to include data for the full spectrum where possible. Main results and conclusions unchange

The Status of Neutralino Dark Matter

The lightest neutralino in supersymmetry is the most studied dark matter candidate. This writeup reviews the status of neutralino dark matter in minimal and nonminimal supersymmetric models in light of recent null results at the XENON100 experiment and the observation of a 130 GeV gamma ray signal from the Galactic Center by the Fermi LAT.Comment: Contribution to the proceedings of the CETUP* 2013 Dark Matter Program, Lead/Deadwood, South Dakot

Comment on Calculation of Positron Flux from Galactic Dark Matter

Energetic positrons produced in annihilation or decay of dark matter particles in the Milky Way can serve as an important indirect signature of dark matter. Computing the positron flux expected in a given dark matter model involves solving transport equations, which account for interaction of positrons with matter and galactic magnetic fields. Existing calculations solve the equations inside the diffusion zone, where galactic magnetic fields confine positrons, and assume vanishing positron density on the boundaries of this zone. However, in many models, a substantial fraction of the dark matter halo lies outside the diffusion zone. Positrons produced there can then enter the diffusion zone and get trapped, potentially reaching the Earth and increasing the expected flux. We calculate this enhancement for a variety of models. We also evaluate the expected enhancement of the flux of energetic photons produced by the inverse Compton scattering of the extra positrons on starlight and cosmic microwave background. We find maximal flux enhancements of order 20% in both cases.Comment: 18 pages, 6 figures. Final version accepted for publication in Physical Review

Exponential Enhancement of Dark Matter Freezeout Abundance

A novel paradigm for thermal dark matter (DM), termed "bouncing dark matter", is presented. In canonical thermal DM scenarios, the DM abundance falls exponentially as the temperature drops below the mass of DM, until thermal freezeout occurs. This note explores a broader class of thermal DM models that are exceptions to this rule, where the DM abundance can deviate from the exponentially falling curve, and even rise exponentially, while in thermal equilibrium. Such scenarios can feature present day DM annihilation cross sections much larger than the canonical thermal target, improving the prospects for indirect detection of DM annihilation signals.Comment: Contribution to SciPost Proceedings of the Identification of Dark Matter (IDM) Conference 202

The Tachyonic Higgs and the Inflationary Universe

The Standard Model Higgs becomes tachyonic at high energy scales according to current measurements. This unstable regime of the Higgs potential can be realized in the early Universe during high scale inflation, potentially with catastrophic consequences. This letter highlights a crucial inherent feature of such configurations that has so far remained ignored: Higgs particle production out of vacuum induced by the rapidly evolving Higgs field, which gets exponentially enhanced due to the tachyonic instability. Such explosive particle production can rapidly drain energy away from the Higgs field, sustaining a significant density of Higgs particles even during inflation, and could initiate a qualitatively different form of preheating in parts of the post-inflationary Universe. Any study of the Higgs field in its tachyonic phase, either during or after inflation, must therefore take this substantial particle energy density into account, which could significantly affect the subsequent evolution of such systems. This could carry important implications for high scale inflation, post-inflationary preheating, observable signals in the cosmic microwave background, gravitational waves, and primordial black holes, as well as deeper concepts ranging from eternal inflation to the metastability of the electroweak vacuum.Comment: 8 pages, 2 figure

Antiprotons from Dark Matter: Effects of a Position-Dependent Diffusion Coefficient

Energetic antiprotons in cosmic rays can serve as an important indirect signature of dark matter. Conventionally, the antiproton flux from dark matter decays or annihilations is calculated by solving the transport equation with a space-independent diffusion coefficient within the diffusion zone of the galaxy, and assuming free propagation outside this zone. Antiproton sources outside of the diffusion zone are ignored. In reality, it is far more likely that the diffusion coefficient increases smoothly with distance from the disk, and the outlying part of the dark matter halo ignored in the conventional approach can be significant, containing as much as 90% of the galactic dark matter by mass in some models. We extend the conventional approach to address these issues. We obtain analytic approximations and numerical solutions for antiproton flux assuming that the diffusion coefficient increases exponentially with the distance from the disk, and including contributions from dark matter annihilations/decays in essentially the full dark matter halo. We find that the antiproton flux predicted in this model deviates from the conventional calculation for the same dark matter parameters by up to about 25%.Comment: minor corrections and clarifications. main results and conclusions unchanged. final version accepted for publication in PR

Right-handed Neutrinos and R(D(∗))R(D^{(*)})

We explore scenarios where the $R(D^{(*)})$ anomalies arise from semitauonic decays to a right-handed sterile neutrino. We perform an EFT study of all five simplified models capable of generating at tree-level the lowest dimension electroweak operators that give rise to this decay. We analyze their compatibility with current $R(D^{(*)})$ data and other relevant hadronic branching ratios, and show that one simplified model is excluded by this analysis. The remainder are compatible with collider constraints on the mediator semileptonic branching ratios, provided the mediator mass is of order TeV. We also discuss the phenomenology of the sterile neutrino itself, which includes possibilities for displaced decays at colliders and direct searches, measurable dark radiation, and gamma ray signals.Comment: 30 pages, 13 figures. Updated collider constraints and discussions. Matches published version in JHE

Searching for Confining Hidden Valleys at the LHC(b)

We explore strategies for probing Hidden Valley scenarios exhibiting confinement. Such scenarios lead to a multiplicity of light hidden hadrons from showering processes. Their decays are typically soft and displaced, making them challenging to probe with traditional LHC searches. We show the low trigger thresholds and excellent track and vertex reconstruction at LHCb provide an ideal environment to search for such signals -- in both muonic and hadronic channels. We also explore the potential of ATLAS/CMS and discuss modifications to present searches that might make these experiments competitive with the LHCb reach. Our proposed searches can probe $Z^{\prime}$ models with dominant decays to dark sectors as well as exotic Higgs boson decays in Twin Higgs models.Comment: 6 pages, 3 figure