The Dark Universe: Primordial Black Hole $\leftrightharpoons$ Dark Graviton Gas Connection

TL;DR

This paper explores a theoretical connection between primordial black holes and a tower of massive gravitons as dark matter candidates within a higher-dimensional framework, proposing a unified picture of their evolution and properties.

Contribution

It introduces a novel correspondence between 5D primordial black holes and KK gravitons, linking their mass evolution and decay processes in a unified dark matter scenario.

Findings

Black holes with mass ~$7 imes 10^{13}$ g mimic KK graviton towers with ~50 keV mass.

Dark gravitons are produced at 1-50 GeV and cool down to 1-100 keV today.

Intra-tower decays of gravitons relate to black hole accretion growth.

Abstract

We study the possible correspondence between 5-dimensional primordial black holes and massive 5-dimensional KK gravitons as dark matter candidate within the recently proposed dark dimension scenario that addresses the cosmological hierarchy problem. First, we show that in the local universe a population of 5-dimensional black holes with $M_{\rm BH}\sim 7\times 10^{13}~{\rm g}$ would be practically indistinguishable from a KK tower of dark gravitons with $m_{\rm DM} \sim 50~{\rm keV}$. Second, we connect the mass increase of 5-dimensional black holes and the related temperature decrease with the cooling of the tower of massive spin-2 KK excitations of the graviton. The dark gravitons are produced at a mass $\sim 1 - 50~{\rm GeV}$ and the bulk of their mass shifts down to roughly $1 - 100~{\rm keV}$ today. The cooling of the system proceeds via decay to lighter gravitons without losing much total mass density, resembling the intra-tower decays that characterize the cosmological evolution of the dynamical dark matter framework. We associate the intra-tower decays of the graviton gas with the black hole growth through accretion. We also discuss that the primordial black hole $\leftrightharpoons$ dark graviton gas connection can be nicely explained by the bound state picture of black holes in terms of gravitons.