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

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 BH ∼ 7 × 10 13 g would be practically indistinguishable from a KK tower of dark gravitons with m DM ∼ 50 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 ∼ 1 − 50 GeV and the bulk of their mass shifts down to roughly 1 − 100 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 dark graviton gas connection can be nicely explained by the bound state picture of black holes in terms of gravitons.

Minimal black holes and species thermodynamics

“…The implications of this outcome find application in the scenario pertaining to the Dark Dimension [40], where we show that temperature and decay rates of near-extremal species can nicely accommodate the properties of KK dark matter particles, as proposed in [41,42]. This result may underline the already recognized link between Dark matter graviton gases and black holes [43].…”

“…Hence, the thermodynamics of near-extremal species naturally provides the desired initial temperature at the time when the dark matter particles are produced. This result emphasizes the already acknowledged connection between dark matter as KK graviton, and black holes in the context of early time universe [43].…”

“…where the upper bound is model-independent and originates from the Higuchi bound [67], while the lower bound can be inferred by considering 1-loop Casimir potentials in d dimensions [40,68]. Applying then constraints from experiments, one is led to the Dark Dimension Scenario [40] and its implications [41,43,[69][70][71][72][73] with d = 4, α = 1/4 and a tower of KK species coming from the compactification of one (large) extra dimension of size 9…”

String Cosmology: from the Early Universe to Today

“…[947] observes that a mesoscopic large extra dimension slows down the rate of Hawking radiation for black holes, thus prolonging the survival of low-mass primordial black holes, which can then compose all of dark matter. The correspondence between a 5-dimensional primordial black hole and 5-dimensional massive KK modes interpretation of dark matter was discussed in [948].…”