Dark matter annihilation at cosmological redshifts: possible relic signal from annihilation of weakly interacting massive particles

Abstract

We discuss the possibility to observe the products of dark matter annihilation that was going on in the early Universe. Of all the particles that could be generated by this process we consider only photons, as they are both uncharged and easily detectable. The earlier the Universe was, the higher the dark matter concentration $n$ and the annihilation rate (proportional to $n^2$) were. However, the emission from the very early Universe cannot reach us because of the opacity. The main part of the signal was generated at the moment the Universe had just become transparent for the photons produced by the annihilation. Thus, the dark matter annihilation in the early Universe should have created a sort of relic emission. We obtain its flux and the spectrum. If weakly interacting massive particles (WIMPs) constitute dark matter, it is shown that we may expect an extragalactic gamma-ray signal in the energy range 0.5 - 20 {MeV} with a maximum near 8 {MeV}. We show that an experimentally observed excess in the gamma-ray background at 0.5 - 20 {MeV} could be created by the relic WIMPs annihilation only if the dark matter structures in the universe had appeared before the universe became transparent for the annihilation products ($z\simeq 300$). We discuss in more detail physical conditions whereby this interpretation could be possible.

arXiv comment8 pages, 3 figures

References in corpus (20)

• First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Determination of Cosmological Parameters
• Supersymmetric Dark Matter
• Cosmological parameters from SDSS and WMAP
• Profiles of dark haloes: evolution, scatter, and environment
• EGRET Observations of the Extragalactic Gamma Ray Emission
• Scalar Dark Matter candidates
• MeV Dark Matter: Has It Been Detected?
• Earth-mass dark-matter haloes as the first structures in the early Universe
• A new determination of the extragalactic diffuse gamma-ray background from EGRET data
• The first WIMPy halos
• Damping scales of neutralino cold dark matter
• Small-scale clumps in the galactic halo and dark matter annihilation
• EGRET Excess of Diffuse Galactic Gamma Rays as Tracer of Dark Matter
• The Concordance Cosmic Star Formation Rate: Implications from and for the Supernova Neutrino and Gamma Ray Backgrounds
• The Cosmic MeV Gamma-ray Background and Hard X-ray Spectra of Active Galactic Nuclei: Implications for the Origin of Hot AGN Coronae
• Dark Matter Annihilation: the origin of cosmic gamma-ray background at 1-20 MeV
• Soft gamma-ray background and light Dark Matter annihilation
• Cosmic gamma-ray background from Type Ia supernovae revisited: Evidence for missing gamma-rays at MeV
• Cosmological Lower Bound on Dark Matter Masses from the Soft Gamma-ray Background
• AGN models for the X and gamma-ray backgrounds

Cited by in corpus (3)

• Polytropic dark matter flows illuminate dark energy and accelerated expansion
• Dark Energy: The Shadowy Reflection of Dark Matter?
• A conventional approach to the dark-energy concept