We discuss a novel mechanism for segregation of baryons and antibaryons in the quark-gluon plasma phase which can lead to formation of quark and antiquark nuggets in the early universe, irrespective of the order of the quark-hadron phase transition. This happens due to $CP$ violating scattering of quarks and antiquarks from moving $Z(3)$ domain walls. $CP$ violation here is spontaneous in nature and arises from the nontrivial profile of the background gauge field ($A_0$) between different $Z(3)$ vacua. We study the effect of this spontaneous $CP$ violation on the baryon transport across the collapsing large $Z(3)$ domain walls (which can arise in the context of certain low energy scale inflationary models). Our results show that this $CP$ violation can lead to large concentrations of baryons and antibaryons in the early universe. The quark and antiquark nuggets, formed by this alternate mechanism, can provide a viable dark matter candidate within standard model without violating any observational constraints.

• Received 25 May 2014

DOI:https://doi.org/10.1103/PhysRevD.90.045010