Accretion Effects on Primordial Black Hole Reheating Constraints

TL;DR

This paper investigates how accretion influences primordial black hole reheating, affecting their mass, abundance, and related gravitational wave constraints, with implications for early universe cosmology.

Contribution

It introduces the impact of accretion on PBH reheating constraints, showing significant shifts in allowed parameters and stronger GW constraints compared to merger limits.

Findings

Accretion increases PBH mass and prolongs matter domination.

Accretion shifts formation mass and abundance constraints to smaller values.

Isocurvature GW constraints are stronger than merger constraints.

Abstract

In this work, we study the effects of accretion on the primordial black hole (PBH) reheating scenario. PBHs could form from primordial fluctuations. If they have the right mass and abundance, they could dominate the Universe and complete the reheating entirely through Hawking radiation. We find accretion effects on the BH can not only increase the BH mass, but also prolong such early matter domination. The consequence of the accretion is further investigated using isocurvature induced gravitational waves (GWs), which are generated right after the sudden evaporation of the BHs from the oscillation of the gravitational potential. Big Bang nucleosynthesis limits on the energy density of the GWs put important constraints on the PBH domination scenario. Inclusion of accretion shifts such constraints significantly towards smaller formation mass and smaller initial abundance. Furthermore, the PBH could undergo mergers leading to extended mass functions. We find similar shifts in the allowed parameters with the inclusion of accretion for the merger constraint. We find the constraints from isocurvature GWs typically stronger than the constraints from mergers.