Known unknowns of dark matter annihilation over cosmic time

Abstract

Dark matter self-annihilation holds promise as one of the most robust mechanisms for the identification of the particle responsible for the Universe's missing mass. In this work, I examine the evolution of the dark matter annihilation power produced by smooth and collapsed structures over cosmic time, taking into account uncertainties in the structure of dark matter haloes. As we search for observational signatures of annihilation, an understanding of this time evolution will help us to best direct our observational efforts, either with local measurements or investigation of the effects of annihilation on the intergalactic medium at high redshift. As I show in this work, there are several key sources of uncertainty in our ability to estimate the darkmatter annihilation from collapsed structures, including: the density profile of darkmatter haloes; the small-scale cut-offin the dark matter halo mass function; the redshift-dependent mass-concentration relation for small haloes; and the particle-velocity dependence of the dark matter annihilation process. Varying assumptions about these quantities can result in annihilation power predictions that differ by several orders of magnitude. These uncertainties must be resolved, through a combination of observation and modelling, before robust estimations of the cosmological annihilation signal can be made. © 2014 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society.