Dynamical black holes in the inflationary epoch

TL;DR

This paper studies the evolution and survivability of black holes during the inflationary epoch, considering their coupling to the universe's expansion, Hawking evaporation, and accretion effects across cosmic eras.

Contribution

It introduces a model of black hole evolution during inflation using generalized McVittie geometry and derives bounds on initial mass for black holes to survive until today.

Findings

Black holes must have initial masses within a narrow range to survive inflation.

Hawking evaporation and accretion impose constraints on black hole mass evolution.

Surviving black holes today can reach a maximum mass of approximately 0.001 solar masses.

Abstract

We investigate the evolution of black holes present during the inflationary epoch, assuming they are dynamically coupled to the cosmological background through a generalized McVittie geometry, such that their gravitational mass scales with the cosmic scale factor. Adopting Starobinsky's $\mathcal{R}^2$ inflation model, we analyse the combined effects of cosmological coupling, Hawking evaporation and radiation accretion during the subsequent cosmic eras: inflation, radiation, matter, and dark energy. Requiring the black hole event horizon to remain smaller than the particle horizon at all times yields an upper bound on the mass parameter. Radiation accretion during the radiation era further constrains the parameter space to prevent runaway growth. Hawking evaporation sets a lower bound on the initial mass to ensure survival through inflation. We find that only black holes formed within a narrow initial mass range during inflation can persist to the present day, reaching a maximum mass of $M(t_0) \simeq 1.043\times10^{-3} M_\odot$.