Asymmetric dark matter

Abstract

We consider a simple class of models in which the relic density of dark matter is determined by the baryon asymmetry of the Universe. In these models a $B\ensuremath{-}L$ asymmetry generated at high temperatures is transferred to the dark matter, which is charged under $B\ensuremath{-}L$. The interactions that transfer the asymmetry decouple at temperatures above the dark matter mass, freezing in a dark matter asymmetry of order the baryon asymmetry. This explains the observed relation between the baryon and dark matter densities for the dark matter mass in the range 5--15 GeV. The symmetric component of the dark matter can annihilate efficiently to light pseudoscalar Higgs particles $a$ or via $t$-channel exchange of new scalar doublets. The first possibility allows for ${h}^{0}\ensuremath{\rightarrow}aa$ decays, while the second predicts a light charged Higgs-like scalar decaying to $\ensuremath{\tau}\ensuremath{\nu}$. Direct detection can arise from Higgs exchange in the first model or a nonzero magnetic moment in the second. In supersymmetric models, the would-be lightest supersymmetric partner can decay into pairs of dark matter particles plus standard model particles, possibly with displaced vertices.