Comprehensive search for dark matter annihilation in dwarf galaxies

Abstract

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 (2.2×10 −26 cm 3 s −1 ) for dark matter masses below 26 GeV (for annihilation into bb), 29 GeV (τ + τ − ), 35 GeV (uū, dd, ss, cc, and gg), 6 GeV (e + e − ), and 114 GeV (γγ). For dark matter particle masses less than 1 TeV, these represent the strongest limits obtained to date using dwarf galaxies.

Scalar simplified models for dark matter

“…For gamma-ray energies (and thus dark matter masses) below approximately a TeV, the Fermi Gamma-Ray Space Telescope (FGST) provides the best bounds at present [80][81][82][83]. In particular in this paper we will use the bounds set by the FGST in Ref.…”

Lepton-flavored scalar dark matter with minimal flavor violation

“…For m S 3 < 20 GeV, the predicted annihilation rate for the τ + τ − final-state is in some tension with upper limits inferred from searches for DM signals in diffuse gamma-ray data from the Fermi Large Area Telescope observations of dwarf spheroidal satellite galaxies of the Milky Way [62][63][64].…”

Dark matter annihilation and decay from non-spherical dark halos in galactic dwarf satellites

“…Until now, for the heavier dark matter mass range, these upper limits are the strictest limits based on observations by ground-based air Cherenkov telescopes. At lower energies, the Large Area Telescope of the Fermi satellite (Fermi-LAT) was able to provide σv < 1.2 × 10 −26 cm 3 s −1 below O(100) GeV particle masses annihilating into bb based on the observational results of several dSphs (Charbonnier et al 2011;Cholis & Salucci 2012;Geringer-Sameth et al 2015a;Ackermann et al 2015). Most recently, MAGIC collaboration (2016) performed a joint analysis of γ-ray data from the MAGIC and Fermi-LAT to obtain severer limits on dark matter candidates, and they improved on the previous upper limits by up to factor of ∼ 2 in the low mass range.…”