New Limits on the Dark Matter Lifetime from Dwarf Spheroidal Galaxies using Fermi-LAT

TL;DR

This study uses six years of Fermi-LAT gamma-ray data from 19 dwarf spheroidal galaxies to set the most stringent limits yet on dark matter decay lifetimes across a wide mass range, improving constraints for certain decay channels.

Contribution

It provides the first robust, high-confidence lower limits on dark matter lifetime from a stacked analysis of multiple dwarf spheroidal galaxies using Fermi-LAT data, with improved sensitivity over previous results.

Findings

Established new lower limits on dark matter decay lifetime for various channels.

Demonstrated that dwarf spheroidal galaxies are highly effective targets for dark matter decay constraints.

Constraints are among the most stringent and are competitive with other astrophysical and cosmological probes.

Abstract

Dwarf spheroidal galaxies (dSphs) are promising targets for the indirect detection of dark matter through gamma-ray emission due to their proximity, lack of astrophysical backgrounds and high dark matter density. They are often used to place restrictive bounds on the dark matter annihilation cross section. In this paper, we analyze six years of {\it Fermi}-LAT gamma-ray data from 19 dSphs that are satellites of the Milky Way, and derive from a stacked analysis of 15 dSphs, robust 95\% confidence level lower limits on the dark matter lifetime for several decay channels and dark matter masses between $\sim 1$GeV and $10$TeV. Our findings are based on a bin-by-bin maximum likelihood analysis treating the J-factor as a nuisance parameter using PASS 8 event-class. Our constraints from this ensemble are among the most stringent and solid in the literature, and competitive with existing ones coming from the extragalactic gamma-ray background, galaxy clusters, AMS-02 cosmic ray data, Super-K and ICECUBE neutrino data, while rather insensitive to systematic uncertainties. In particular, among gamma-ray searches, we improve existing limits for dark matter decaying into $\bar{b}b$, ($\mu^+\mu^-$) for DM masses below $\sim 30\, (200)$~GeV, demonstrating that dSphs are compelling targets for constraining dark matter decay lifetimes.