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 $M_{\mathrm{BH}}\sim 7\times 10^{13}\mathrm{g}$ would be practically indistinguishable from a KK tower of dark gravitons with $m_{\mathrm{DM}}\sim 50\mathrm{keV}$. 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 $\sim 1-50\mathrm{GeV}$ and the bulk of their mass shifts down to roughly $1-100\mathrm{keV}$ 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.

Comments: 4 pages, 2 figures. arXiv admin note: text overlap with arXiv:2206.07071, revised version to appear in PLB