Primordial black holes in braneworld cosmologies: Astrophysical constraints

Abstract

In two recent papers we explored the modifications to primordial black hole physics when one moves to the simplest braneworld model, Randall-Sundrum type II. Both the evaporation law and the cosmological evolution of the population can be modified, and additionally accretion of energy from the background can be dominant over evaporation at high energies. In this paper we present a detailed study of how this impacts upon various astrophysical constraints, analyzing constraints from the present density, from the present high-energy photon background radiation, from distortion of the microwave background spectrum, and from processes affecting light element abundances both during and after nucleosynthesis. Typically, the constraints on the formation rate of primordial black holes weaken as compared to the standard cosmology if black hole accretion is unimportant at high energies, but can be strengthened in the case of efficient accretion.

Scalar perturbations in braneworld cosmology

“…the greater gravitational force of attraction in the early universe will create more of these objects than in GR (different aspects of primordial black holes in RS cosmology in the context of various effective theories have been considered in Refs. [41,42,43,44,45,46,47]). We know that the abundance of primordial black holes can be constrained by big bang nucleosythesis and observations of high-energy cosmic rays, so it would be interesting to see if the kind of enhancement of density perturbations predicted in this paper can be used to derive new limits on Randall-Sundrum cosmology.…”

Braneworld Black Holes in Cosmology and Astrophysics

“…The decaying black holes affect several cosmological processes at different eras, and hence the observational abundance of different species, for example, the background high enery photons 65 , could be used to put constraints on the initial mass spectrum of the black holes. These contraints have to be evaluated considering the altered cosmological evolution in the braneworld scenario, and therefore could be significantly modified compared to similar constraints in standard cosmology 22 . The exchange of energy of the black holes with the surrounding radiation in the high energy era leads to mass disequilibration of neighbouring black holes 23 .…”

“…Observational results such as the background gamma ray spectrum could hence be used to impose constaints on the initial mass spectrum of the black holes. These could be again significantly modified 22 compared to those that have been obtained for primordial Schwarzschild black holes in standard cosmology.…”

“…Clancy et al 22 have shown how standard constraints are modified in the case of braneworld cosmology. To simplify the treatment, one can assume that radiation domination persists up to t c , and that the accretion of radiation is possible only up to t c .…”

“…(5)). For these reasons only this particular form (13) of braneworld black hole geometry has been considered for the analysis of cosmological evolution 19,20,21,22 . We first consider the evolution of a single primordial black hole which is formed with a sub-horizon mass 19 in the high energy radiation dominated era.…”