Black Hole Astrophysics in AdS Braneworlds

TL;DR

Problem: The RS2 braneworld with a large AdS radius implies a vast hidden CFT sector that can dramatically shorten brane-localized black hole lifetimes. Approach: The authors apply AdS/CFT to model black hole evolution as Hawking radiation into a large number of CFT degrees of freedom, incorporating greybody corrections, and compare to environmental accretion. Findings: Large black holes evaporate rapidly for modest $L$, yielding strong bounds on $L$ from X-ray binaries, MACHOs, and primordial BHs; near-bound scenarios could produce dramatic final-stage detonations. Significance: The work provides a powerful astrophysical probe of extra dimensions and hidden-sector degrees of freedom, offering observational signatures and guiding future searches.

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.