PBH runaway during reheating
Abstract
The growth of primordial black holes through the absorption of the surrounding plasma has recently been shown to exhibit a critical behavior during radiation domination. We extend this analysis to the reheating era and derive analytical solutions for general reheating histories. We show that reheating modifies the critical condition for runaway absorption, making it dependent on both the reheating dynamics and the black-hole formation time. We identify two distinct regimes: runaway growth occurring during reheating, or being triggered after the onset of radiation domination by the mass accumulated during reheating. More generally, we derive a simple composition law describing how independent mass- growth mechanisms combine across successive cosmological eras. Applying it to radiation absorption and inflaton accretion, we obtain analytical results in excellent agreement with the full numerical evolution.
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BibTeX
@misc{haque2026runaway,
title = {{PBH runaway during reheating}},
author = {Md Riajul Haque and Mathieu Gross and Mathieu Houlier and Yann Mambrini},
howpublished = {HAL},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.10696},
eprint = {2609.10696},
archivePrefix = {arXiv},
url = {https://hal.science/hal-05759389v1},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - PBH runaway during reheating
AU - Md Riajul Haque
AU - Mathieu Gross
AU - Mathieu Houlier
AU - Yann Mambrini
PY - 2026
DA - 2026/09/09
PB - HAL
DO - 10.48550/arxiv.2609.10696
UR - https://hal.science/hal-05759389v1
AB - The growth of primordial black holes through the absorption of the surrounding plasma has recently been shown to exhibit a critical behavior during radiation domination. We extend this analysis to the reheating era and derive analytical solutions for general reheating histories. We show that reheating modifies the critical condition for runaway absorption, making it dependent on both the reheating dynamics and the black-hole formation time. We identify two distinct regimes: runaway growth occurring during reheating, or being triggered after the onset of radiation domination by the mass accumulated during reheating. More generally, we derive a simple composition law describing how independent mass- growth mechanisms combine across successive cosmological eras. Applying it to radiation absorption and inflaton accretion, we obtain analytical results in excellent agreement with the full numerical evolution.
ER -