Asymmetric dark matter

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 $B-L$ asymmetry generated at high temperatures is transferred to the dark matter, which is charged under $B-L$. 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 $h^0\to aa$ decays, while the second predicts a light charged Higgs-like scalar decaying to $\tau \nu$. 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.