Constraints on decaying dark matter from the extragalactic gamma-ray background

TL;DR

This paper constrains the lifetime of decaying dark matter using Fermi gamma-ray data, excluding many models especially those explaining positron excess, with robust limits across a wide mass range.

Contribution

It provides the most stringent and astrophysics-uncertainty-resilient constraints on decaying dark matter lifetime from extragalactic gamma-ray background analysis.

Findings

Dark matter lifetime shorter than 10^28 seconds is excluded for masses 100 GeV to 1 TeV.

Most models explaining positron excess are ruled out by these constraints.

Constraints are robust against astrophysical modeling uncertainties.

Abstract

If dark matter is unstable and the mass is within GeV-TeV regime, its decays produce high-energy photons that give contribution to the extragalactic gamma-ray background (EGRB). We constrain dark matter decay by analyzing the 50-month EGRB data measured with Fermi satellite, for different decay channels motivated with several supersymmetric scenarios featuring R-parity violation. We adopt the latest astrophysical models for various source classes such as active galactic nuclei and star-forming galaxies, and take associated uncertainties properly into account. The lower limits for the lifetime are very stringent for a wide range of dark matter mass, excluding the lifetime shorter than 10^28 s for mass between a few hundred GeV and ~1TeV, e.g., for b\bar{b} decay channel. Furthermore, most dark matter models that explain the anomalous positron excess are also excluded. These constraints are robust, being little dependent on astrophysical uncertainties, unlike other probes such as Galactic positrons or anti-protons.