Baryogenesis from Primordial Blackholes after Electroweak Phase Transition

Abstract

Incorporating a realistic model for accretion of ultra-relativistic particles by primordial blackholes (PBHs), we study the evolution of an Einstein-de Sitter universe consisting of PBHs embedded in a thermal bath from the epoch $\sim 10^{-33}$ sec to $\sim 5\times 10^{-9}$ sec. In this paper we use Barrow et al's ansatz to model blackhole evaporation in which the modified Hawking temperature goes to zero in the limit of the blackhole attaining a relic state with mass $\sim m_{pl}$. Both single mass PBH case as well as the case in which blackhole masses are distributed in the range $8\times 10^2 - 3\times 10^5$ gm have been considered in our analysis. Blackholes with mass larger than $\sim 10^5$ gm appear to survive beyond the electroweak phase transition and, therefore, successfully manage to create baryon excess via $X-\bar X$ emissions, averting the baryon number wash-out due to sphalerons. In this scenario, we find that the contribution to the baryon-to-entropy ratio by PBHs of initial mass $m$ is given by $\sim \epsilon \zeta (m/1 {gm})^{-1}$, where $\epsilon$ and $\zeta$ are the CP-violating parameter and the initial mass fraction of the PBHs, respectively. For $\epsilon $ larger than $\sim 10^{-4}$, the observed matter-antimatter asymmetry in the universe can be attributed to the evaporation of PBHs.