Dark Matter and the Baryon Asymmetry

Abstract

We present a mechanism to generate the baryon asymmetry of the Universe which preserves the net baryon number created in the Big Bang. If dark matter particles carry baryon number $B_X$, and ${\sigma }_{\bar{X}}^{\mathrm{annih}}<{\sigma }_X^{\mathrm{annih}}$, the $\bar{X}$'s freeze out at a higher temperature and have a larger relic density than $X$'s. If $m_X \lsi 4.5 B_X $GeV and the annihilation cross sections differ by $\mathcal{O}$(10%) or more, this type of scenario naturally explains the observed ${\Omega }_{DM}\approx 5{\Omega }_b$. Two concrete examples are given, one of which can be excluded on observational grounds.