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Carr criterion and mass gaps in non-singular primordial black hole formation

gr-qc2026-05v1license

Abstract

Non-singular gravitational theories are expected to be relevant in the early universe. In this paper, we derive a set of effective Friedmann equations describing the dynamics of matter shells in the presence of a gravitational regulator \ell. We find that such a regulator induces a primordial black hole mass gap such that below a certain mass Mgap(,RH)M_\text{gap}(\ell, R_H) no black holes can form. The order of magnitude of this mass gap is set by the regulator c2/G\sim c^2\ell/G, with subleading dependence on the horizon radius at time of formation RHR_H. Finally, we show that over a wide range of equation of state parameters ω=01/3\omega = 0 \dots 1/3, the mass gap implies a Carr criterion of the form δH>2GMgap/RH1\delta_H > 2G M_\text{gap}/R_H - 1. If the horizon size is of the same order of the regulator, RHR_H \sim \ell, this new criterion is stronger than the traditional Carr criterion for primordial black hole formation. This connects the primordial black hole abundance directly to the presence of gravitational regulators.

Comments: 8 pages, 3 figures, comments welcome!

Cite

@article{arxiv.2605.30340,
  title  = {Carr criterion and mass gaps in non-singular primordial black hole formation},
  author = {Jens Boos and Arif Kağan Gündoğdu and Marek Hartenfels},
  journal= {arXiv preprint arXiv:2605.30340},
  year   = {2026}
}