Matter-antimatter asymmetry and dark matter stability from baryon number conservation

Abstract: There is currently no evidence for a baryon asymmetry in our Universe. Instead, cosmological observations have only demonstrated the existence of a quark-antiquark asymmetry, which does not necessarily imply a baryon asymmetric Universe, since the baryon number of the dark sector particles is unknown. In this paper we discuss a framework where the total baryon number of the Universe is equal to zero, and where the observed quark-antiquark asymmetry arises from neutron portal interactions with a dark sector fermion $N$ that carries baryon number. In order to render a baryon symmetric universe throughout the whole cosmological history, we introduce a complex scalar $\chi$, with opposite baryon number and with the same initial abundance as $N$. Notably, due to the baryon number conservation, $\chi$ is absolutely stable and could have an abundance today equal to the observed dark matter abundance. Therefore, in this simple framework, the existence of a quark-antiquark asymmetry is intimately related to the existence (and the stability) of dark matter.