Black Hole Astrophysics in AdS Braneworlds

TL;DR

This paper explores how large black holes in the Randall-Sundrum braneworld model rapidly evaporate via Hawking radiation into conformal field theory modes, providing astrophysical bounds on the AdS radius.

Contribution

It demonstrates that black hole evaporation in RS2 models is significantly enhanced by CFT modes, leading to observable astrophysical signatures and new bounds on the AdS radius.

Findings

Black holes of a few solar masses could evaporate in 10^4-10^5 years for L ~ 0.1 mm.

Persistence of X-ray binaries constrains the AdS radius to less than 10^-2 mm.

Observation of primordial black holes could tighten bounds to a few times 10^-6 mm.

Abstract

We consider astrophysics of large black holes localized on the brane in the infinite Randall-Sundrum model. Using their description in terms of a conformal field theory (CFT) coupled to gravity, deduced in Ref. [1], we show that they undergo a period of rapid decay via Hawking radiation of CFT modes. For example, a black hole of mass ${\rm few} \times M_\odot$ would shed most of its mass in $\sim 10^4 - 10^5$ years if the AdS radius is $L \sim 10^{-1}$ mm, currently the upper bound from table-top experiments. Since this is within the mass range of X-ray binary systems containing a black hole, the evaporation enhanced by the hidden sector CFT modes could cause the disappearance of X-ray sources on the sky. This would be a striking signature of RS2 with a large AdS radius. Alternatively, for shorter AdS radii, the evaporation would be slower. In such cases, the persistence of X-ray binaries with black holes already implies an upper bound on the AdS radius of $L \la 10^{-2}$ mm, an order of magnitude better than the bounds from table-top experiments. The observation of primordial black holes with a mass in the MACHO range $M \sim 0.1 - 0.5 M_\odot$ and an age comparable to the age of the universe would further strengthen the bound on the AdS radius to $L \la {\rm few} \times 10^{-6} $ mm.