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arXiv · 2603.24759

Primordial black hole formation from transient $f(T)$ cosmology

Gerasimos Kouniatalis·Theodoros Papanikolaou·Spyros Basilakos·Emmanuel N. Saridakis
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Abstract

We study primordial black hole (PBH) formation in a minimally coupled $f(T)$ teleparallel cosmology that generates a transient departure from standard radiation domination. The model is constructed so that modified-gravity effects are negligible at early and late times, but become dynamically relevant over a finite epoch, during which an effective torsion component reduces the total equation-of-state parameter below 1/3.We show that this transient softening lowers the collapse threshold for overdensities at horizon re-entry, leading to an exponential enhancement of PBH formation. In addition, the modified background alters the relation between temperature and horizon mass, producing a localized feature in the PBH mass function. For representative parameters, PBHs with asteroid-scale masses can account for a significant fraction, or even the entirety, of dark matter for perturbation amplitudes $\sigma^2 \sim \mathcal{O}(10^{-3})$, while remaining consistent with current constraints. Our results demonstrate that modified gravity alone can efficiently generate PBHs, without requiring ad hoc modifications of the radiation sector.

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Gerasimos Kouniatalis, Theodoros Papanikolaou, Spyros Basilakos, Emmanuel N. Saridakis. 2026-03-25. Primordial black hole formation from transient $f(T)$ cosmology. https://doi.org/10.1016/j.dark.2026.102418

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