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arXiv · 2610.26482

Primordial black holes in braneworld gravity: A gateway to hidden dimensions and the dark Universe

Itzi Aldecoa-Tamayo
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Abstract

This thesis investigates the cosmological dynamics of primordial black holes (PBHs) within the Randall--Sundrum Type II braneworld scenario. The work comprises a preliminary discussion on gravitational collapse in the small-black-hole limit at early cosmological epochs, and two principal studies. The first study presents a fully relativistic treatment of PBH accretion in the early Universe, employing Michel accretion theory within the covariant Shiromizu--Maeda--Sasaki formalism. The analysis reveals that higher-dimensional effects substantially enhance early-time accretion onto light PBHs, with discrepancies between our black hole masses and previous estimates growing with cosmic time as $t^{0.33}$ --- a difference that reaches several orders of magnitude by the end of the strong-accretion epoch. This finding fundamentally alters the mapping between the initial PBH mass spectrum and present-day populations. The second study reassesses the observational and cosmological constraints on higher-dimensional PBHs in Randall--Sundrum cosmologies. Constraints from direct Hawking radiation, unresolved diffuse gamma-ray backgrounds, microlensing surveys, and energy injection into the cosmic microwave background are reanalysed in light of the modified higher-dimensional evaporation dynamics and updated observational surveys. Taken together, these results identify viable regions of parameter space in which PBHs can account for the entirety of dark matter while remaining consistent with current observational bounds. Notably, due to the enhanced accretion epoch, PBHs capable of constituting a significant fraction of dark matter may originate from masses below the effective four-dimensional Planck scale. This thesis thus puts forward a dark matter candidate with a distinct evolutionary history and observational signatures today.

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Itzi Aldecoa-Tamayo. 2026-10-19. Primordial black holes in braneworld gravity: A gateway to hidden dimensions and the dark Universe. https://arxiv.org/abs/2610.26482

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