arXiv subjects

Alex Geringer-Sameth

Publications and source records attributed to Alex Geringer-Sameth.

25 records · Page 2Linked to original sources

arXiv2015

A Comprehensive Search for Dark Matter Annihilation in Dwarf Galaxies

We present a new formalism designed to discover dark matter annihilation occurring in the Milky Way's dwarf galaxies. The statistical framework extracts all available information in the data by simultaneously combining observations of all the dwarf galaxies and incorporating the impact of particle physics properties, the distribution of dark matter in the dwarfs, and the detector response. The method performs maximally powerful frequentist searches and produces confidence limits on particle physics parameters. Probability distributions of test statistics under various hypotheses are constructed exactly, without relying on large sample approximations. The derived limits have proper coverage by construction and claims of detection are not biased by imperfect background modeling. We implement this formalism using data from the Fermi Gamma-ray Space Telescope to search for an annihilation signal in the complete sample of Milky Way dwarfs whose dark matter distributions can be reliably determined. We find that the observed data is consistent with background for each of the dwarf galaxies individually as well as in a joint analysis. The strongest constraints are at small dark matter particle masses. Taking the median of the systematic uncertainty in dwarf density profiles, the cross section upper limits are below the pure s-wave weak scale relic abundance value (2.2 x 10^-26 cm^3/s) for dark matter masses below 26 GeV (for annihilation into b quarks), 29 GeV (tau leptons), 35 GeV (up, down, strange, and charm quarks and gluons), 6 GeV (electrons/positrons), and 114 GeV (two-photon final state). For dark matter particle masses less than 1 TeV, these represent the strongest limits obtained to date using dwarf galaxies.

astro-ph.CO↗

arXiv2013

CF2 White Paper: Status and Prospects of The VERITAS Indirect Dark Matter Detection Program

In this white paper, submitted as a part of Snowmass 2013 (subgroup CF2), we examine the current status and future prospects of the VERITAS indirect dark matter detection program. The VERITAS array of imaging atmospheric Cherenkov telescopes (IACTs), sensitive in the 0.1-50 TeV regime, is in the process of completing a multi-year program aimed at detecting signatures of neutralino dark matter. This program is spread out over a range of astrophysical targets which can potentially yield definitive signatures of neutralino self-annihilation such as dwarf spheroidal galaxies (dSphs) and the center of the Milky Way galaxy. While the program is still in progress, initial results on dSphs have produced very competitive upper limits on the thermally averaged cross-section of neutralino self-annihilation as well as strongly constraining leptophillic dark matter models (such as those inferred from the PAMELA and AMS positron fraction results). As the program continues over the next 5 years, VERITAS observations will yield some of the strongest constraints available from IACTs, pushing down the limit on the thermally averaged cross-section of neutralino self-annihilation to the expected natural thermal relic scale.

astro-ph.HE↗

arXiv2013

The VERITAS Dark Matter Program

The VERITAS array of Cherenkov telescopes, designed for the detection of gamma-rays in the 100 GeV-10 TeV energy range, performs dark matter searches over a wide variety of targets. VERITAS continues to carry out focused observations of dwarf spheroidal galaxies in the Local Group, of the Milky Way galactic center, and of Fermi-LAT unidentified sources. This report presents our extensive observations of these targets, new statistical techniques, and current constraints on dark matter particle physics derived from these observations.

astro-ph.HE↗

arXiv2012

Dark matter line search using a joint analysis of dwarf galaxies with the Fermi Gamma-ray Space Telescope

We perform a joint analysis of dwarf galaxy data from the Fermi Gamma-ray Space Telescope in search of dark matter annihilation into a gamma-ray line. We employ a novel statistical method that takes into account the spatial and spectral information of individual photon events from a sample of seven dwarf galaxies. Dwarf galaxies show no evidence of a gamma-ray line between 10 GeV and 1 TeV. The subsequent upper limit on the annihilation cross section to a two-photon final state is 3.9(+7.1)(-3.7) x 10^-26 cm^3/s at 130 GeV, where the errors reflect the systematic uncertainty in the distribution of dark matter within the dwarf galaxies.

astro-ph.HE↗

arXiv2012

Detecting unresolved moving sources in a diffuse background

We present a statistical technique which can be used to detect the presence and properties of moving sources contributing to a diffuse background. The method is a generalization of the 2-point correlation function to include temporal as well as spatial information. We develop a formalism which allows for a derivation of the spacetime 2-point function in terms of the properties of the contributing sources. We test this technique in simulated sky maps, and demonstrate its robustness in identifying the presence of moving and stationary sources. Applications of this formalism to the diffuse gamma-ray background include searches for solar system bodies, fast moving primordial black holes, and dense cores of dark matter proto-halos in the solar neighborhood. Other applications include detecting the contribution of energetic neutrinos originating in the solar system, as well as probing compact objects in long timeline lensing experiments.

astro-ph.HE↗

arXiv2011

Exclusion of canonical WIMPs by the joint analysis of Milky Way dwarfs with Fermi

Dwarf spheroidal galaxies are known to be excellent targets for the detection of annihilating dark matter. We present new limits on the annihilation cross section of Weakly Interacting Massive Particles (WIMPs) based on the joint analysis of seven Milky Way dwarfs using a frequentist Neyman construction and Pass 7 data from the Fermi Gamma-ray Space Telescope. We exclude generic WIMP candidates annihilating into b-bbar with mass less than 40 GeV that reproduce the observed relic abundance. To within 95% systematic errors on the dark matter distribution within the dwarfs, the mass lower limit can be as low as 19 GeV or as high as 240 GeV. For annihilation into tau+tau- these limits become 19 GeV, 13 GeV, and 80 GeV respectively.

astro-ph.CO↗

arXiv2011

Extracting the unresolved pulsar contribution to the gamma-ray background

We present a statistical framework which can be used to determine the contribution of an unresolved population of pulsars to the gamma-ray background. This formalism is based on the joint analysis of photon time series over extended regions of the sky. We demonstrate the robustness of this technique in controlled simulations of pulsar populations, and show that the Fermi Gamma-ray Space Telescope can be used to detect a pulsar contribution as small as 0.1% of the gamma-ray background. This technique is sensitive to pulsar populations with photon fluxes greater than ~1E-10 cm^-2 s^-1. The framework is extensible to arbitrarily complex searches for periodicity and can therefore be tailored to specific applications such as all-sky surveys and studies of the Galactic center and globular clusters.

astro-ph.HE↗