Asymmetric Reheating by Primordial Black Holes

TL;DR

This paper explores how primordial black holes can asymmetrically reheat the visible and dark sectors before BBN, influencing dark matter phenomenology and thermal history without relying on inflaton or modulus interactions.

Contribution

It introduces a novel mechanism of asymmetric reheating via PBH evaporation, providing parametric control over dark sector temperatures and exploring diverse thermal histories.

Findings

PBH evaporation can produce asymmetric reheating of sectors.

Different dark matter thermal histories are consistent with relic abundance.

PBH-dominated scenarios reheat both sectors, affecting cosmological evolution.

Abstract

We investigate Hawking evaporation of a population of primordial black holes (PBHs) prior to Big Bang Nucleosynthesis (BBN) as a mechanism to achieve asymmetric reheating of two sectors coupled solely by gravity. While the visible sector is reheated by the inflaton or a modulus, the dark sector is reheated by PBHs. Compared to inflationary or modular reheating of both sectors, there are two advantages: $(i)$ inflaton or moduli mediated operators that can subsequently thermalize the dark sector with the visible sector are not relevant to the asymmetric reheating process; $(ii)$ the mass and abundance of the PBHs provide parametric control of the thermal history of the dark sector, and in particular the ratio of the temperatures of the two sectors. Asymmetric reheating with PBHs turns out to have a particularly rich dark sector phenomenology, which we explore using a single self-interacting real scalar field in the dark sector as a template. Four thermal histories, involving non-relativistic and relativistic dark matter (DM) at chemical equilibrium, followed by the presence or absence of cannibalism, are explored. These histories are then constrained by the observed relic abundance in the current Universe and the Bullet Cluster. The case where PBHs dominate the energy density of the Universe, and reheat both the visible as well as the dark sectors, is also treated in detail.