Dark matter dynamics in the early universe

Abstract

We study a new form of dark matter interaction which may significantly affect the thermal relic abundance of dark matter. This new interaction takes the form C+D --> C+[phi], where D is the dark matter species present today, [phi] is a standard model species, and C is a very heavy exotic particle. In particular, C was present during the period when freeze-out occurred for dark matter species D, but subsequently decayed into standard model particles. We refer to this process as a catalytic reaction, since C acts as a catalyst for the destruction of D. We further postulate that there is a matter-antimatter asymmetry in C, so that C+C --> D+[phi] is suppressed. We find that the catalytic reaction produces very different dynamics than the standard annihilation reaction. We also find that the catalytic reaction can significantly affect the relic abundance of dark matter even if it has a much smaller cross section than the annihilation reaction. Possible physical origins for this catalytic reaction are discussed.