Spectral Gamma-ray Signatures of Cosmological Dark Matter Annihilation

TL;DR

A new signature for weakly interacting massive particle (WIMP) dark matter is proposed, a spectral feature in the diffuse extragalactic gamma-ray radiation that comes from the asymmetric distortion of the line due to WIMP annihilation into two gamma rays caused by the cosmological redshift.

Abstract

We propose a new signature for weakly interacting massive particle (WIMP) dark matter, a spectral feature in the diffuse extragalactic gamma-ray radiation. This feature, a sudden drop of the gamma-ray intensity at an energy corresponding to the WIMP mass, comes from the asymmetric distortion of the line due to WIMP annihilation into two gamma-rays caused by the cosmological redshift. Unlike other proposed searches for a line signal, this method is not very sensitive to the exact dark matter density distribution in halos and subhalos. The only requirement is that the mass distribution of substructure on small scales follows approximately the Press-Schechter law, and that smaller halos are on the average denser than large halos, which is a generic outcome of N-body simulations of Cold Dark Matter, and which has observational support. The upcoming Gamma-ray Large Area Space Telescope (GLAST) will be eminently suited to search for these spectral features. For numerical examples, we use rates computed for supersymmetric particle dark matter, where a detectable signal is possible.

Figures (1)

• Figure 1: The predicted diffuse $\gamma$-ray flux, from cosmic annihilations into continuum gamma-rays, and a gamma-ray line. The redshifted line gives the conspicuous feature at the highest energies. Shown are cosmic annihilation of 86 GeV (solid line) and 166 GeV (dotted line) neutralinos. A Moore density profile for the halo substructure has been assumed. The EGRET data sreekumar on the extragalactic flux are the data points with error bars shown.