Bounds on cross sections and lifetimes for dark matter annihilation and decay into charged leptons from gamma-ray observations of dwarf galaxies

Abstract

We provide conservative bounds on the dark matter cross-section and lifetime from final state radiation produced by annihilation or decay into charged leptons, either directly or via an intermediate particle φ. Our analysis utilizes the experimental gamma-ray flux upper limits from four Milky Way dwarf satellites: HESS observations of Sagittarius and VERITAS observations of Draco, Ursa Minor, and Willman 1. Using 90% confidence level lower limits on the integrals over the dark matter distributions, we find that these constraints are largely unable to rule out dark matter annihilations or decays as an explanation of the PAMELA and ATIC/PPB-BETS excesses. However, if there is an additional Sommerfeld enhancement in dwarfs, which have a velocity dispersion ∼ 10 to 20 times lower than that of the local Galactic halo, then the cross-sections for dark matter annihilating through φ's required to explain the excesses are very close to the cross-section upper bounds from Willman 1. Dark matter annihilation directly into τ 's is also marginally ruled out by Willman 1 as an explanation of the excesses, and the required cross-section is only a factor of a few below the upper bound from Draco. Finally, we make predictions for the gamma-ray flux expected from the dwarf galaxy Segue 1 for the Fermi Gamma-ray Space Telescope. We find that for a sizeable fraction of the parameter space in which dark matter annihilation into charged leptons explains the PAMELA excess, Fermi has good prospects for detecting a gamma-ray signal from Segue 1 after one year of observation.

Cosmic ray anomalies from the MSSM?

“…A point is shown for each model, orange points corresponding to pMSSM models for which Ωh 2 | LSP ≥ 0.1. The red line represents the estimated sensitivity for the LAT to detect a point source signal at high galactic latitudes with 3σ confidence [103].…”

“…12 Although, as emphasized in [46,103], stellar kinematic data fix the normalization of ρ and ρ 2 such that the detailed nature of the inner-slope of the halo ends up having a relatively small effect on the total halo integral. 13 A rough calculation of these contributions (without any attempt to include the LAT instrument response) showed that the line contribution to the total yield of gammas would be > 1% in only ≈ 0.5% of the models in our pMSSM set.…”

“…Discovered relatively recently in analyses of SDSS data [101], Segue 1 is known to have a mass-to-light ratio M/L ∼ 1000(M /L ), and a preliminary analysis has been carried out to estimate its DM content using the kinematics of 24 of its member stars [102]. We will use the analysis presented in [103], appropriate to the FERMI-LAT observations of Segue 1, in which the line-of-sight halo integral was estimated by marginalizing over halo distributions, including both cusped and cored types. 12 The work [103] has recently been updated and expanded in [104].…”

“…We will use the analysis presented in [103], appropriate to the FERMI-LAT observations of Segue 1, in which the line-of-sight halo integral was estimated by marginalizing over halo distributions, including both cusped and cored types. 12 The work [103] has recently been updated and expanded in [104].…”

Leptonic dark matter annihilation in the evolving universe: constraints and implications

“…Shortly after the proposal of using DM annihilation to account for the data, the γ-ray and radio emissions from the Galactic center [13][14][15], the Milky Way halo [16][17][18][19][20], the dwarf galaxies [21][22][23], the galaxy clusters [24,25] and the early Universe [26][27][28] were studied as possible constraints and/or future probes of the DM models. These studies have shown that the proposed DM scenarios are either excluded or at least strongly constrained if the DM halo properties derived from current numerical simulations are adopted.…”