Baryogenesis from primordial black holes after the electroweak phase transition

Abstract

Incorporating a realistic model for accretion of ultrarelativistic particles by primordial black holes (PBHs), we study the evolution of an Einstein--de Sitter universe consisting of PBHs embedded in a thermal bath from the epoch $\ensuremath{\sim}{10}^{\ensuremath{-}33}\mathrm{sec}$ to $\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\mathrm{sec}.$ In this paper we use the ansatz of Barrow et al. to model black hole evaporation in which the modified Hawking temperature goes to zero in the limit of the black hole attaining a relic state with a mass $\ensuremath{\sim}{m}_{\mathrm{Pl}}.$ Both the single mass PBH case as well as the case in which black hole masses are distributed in the range $8\ifmmode\times\else\texttimes\fi{}{10}^{2}--3\ifmmode\times\else\texttimes\fi{}{10}^{5}\mathrm{g}$ have been considered in our analysis. Black holes with a mass larger than $\ensuremath{\sim}{10}^{5}\mathrm{g}$ appear to survive beyond the electroweak phase transition and, therefore, successfully manage to create baryon excess via $X\ensuremath{-}\overline{X}$ emissions, averting the baryon number washout 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 $\ensuremath{\sim}\ensuremath{\epsilon}\ensuremath{\zeta}(m/1\mathrm{g}{)}^{\ensuremath{-}1},$ where \ensuremath{\epsilon} and \ensuremath{\zeta} are the CP-violating parameter and the initial mass fraction of the PBHs, respectively. For \ensuremath{\epsilon} larger than $\ensuremath{\sim}{10}^{\ensuremath{-}4},$ the observed matter-antimatter asymmetry in the universe can be attributed to the evaporation of PBHs.