Primordial black hole formation in bulk-viscous cosmology
Abstract
We investigate primordial black hole (PBH) formation in a cosmological background with bulk viscosity. Using numerical simulations, we determine the collapse threshold and the resulting PBH mass. We find that the critical threshold μc retains a dependence on the equation-of-state parameter w similar to that in the inviscid case, but is enhanced by an amount comparable to the bulk-viscosity strength ε. For fixed w, the increase in μc is approximately linear in ε. By fitting the standard critical-scaling law for near-threshold collapse, we find that the bulk viscosity leads to an enhancement in the resulting PBH mass. These results indicate that bulk viscosity can systematically modify both the PBH threshold and PBH mass scaling law in the early Universe.
Versions
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BibTeX
@misc{yuwen2026primordial,
title = {{Primordial black hole formation in bulk-viscous cosmology}},
author = {Zi-Yan Yuwen and Cristian Joana and Shao-Jiang Wang and Rong-Gen Cai},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2606.26532},
eprint = {2606.26532},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.26532},
}
RIS
TY - UNPB
TI - Primordial black hole formation in bulk-viscous cosmology
AU - Zi-Yan Yuwen
AU - Cristian Joana
AU - Shao-Jiang Wang
AU - Rong-Gen Cai
PY - 2026
DA - 2026/10/21
PB - arXiv
DO - 10.48550/arxiv.2606.26532
UR - https://arxiv.org/abs/2606.26532
AB - We investigate primordial black hole (PBH) formation in a cosmological background with bulk viscosity. Using numerical simulations, we determine the collapse threshold and the resulting PBH mass. We find that the critical threshold μ_c retains a dependence on the equation-of-state parameter w similar to that in the inviscid case, but is enhanced by an amount comparable to the bulk-viscosity strength ε. For fixed w, the increase in μ_c is approximately linear in ε. By fitting the standard critical-scaling law for near-threshold collapse, we find that the bulk viscosity leads to an enhancement in the resulting PBH mass. These results indicate that bulk viscosity can systematically modify both the PBH threshold and PBH mass scaling law in the early Universe.
ER -