Upper bounds on asymmetric dark matter self annihilation cross sections

Abstract

Most models for asymmetric dark matter allow for dark matter selfannihilation processes, which can wash out the asymmetry at temperaturesnear and below the dark matter mass. We study the coupled set ofBoltzmann equations for the symmetric and antisymmetric dark matternumber densities, and derive conditions applicable to a large class ofmodels for the absence of a significant wash-out of an asymmetry. Theseconstraints are applied to various existing scenarios. In the case ofleft- or right-handed sneutrinos, very large electroweak gaugino masses,or very small mixing angles are required.