Stellar signatures of inhomogeneous big bang nucleosynthesis

Abstract

We evaluate abundance anomalies generated in patches of the Universe where the baryon-to-photon ratio was locally enhanced by possibly many orders of magnitude in the range η ¼ 10 −10-10 −1. Our study is motivated by the possible survival of rare dense regions in the early Universe, the most extreme of which, above a critical threshold, collapsed to form primordial black holes. If this occurred, one may expect there to also be a significant population of early-forming stars that formed in similar but subthreshold patches. We derive a range of element abundance signatures by performing BBN simulations at high values of the baryon-to-photon ratio that may be detectable in any surviving first-generation stars of around a solar mass. Our predictions apply to metal-poor Galactic halo stars, to old globular star clusters, and to dwarf galaxies, and we compare with observations in each of these cases.

Primordial Kerr Black Holes

“…We have shown in Ref. [10] that it would be impossible to detect Hawking radiation of P9 from Earth, and not even with a probe travelling towards P9, because of the blackbody radiation from the Cosmic Microwave Background (CMB). However, a satellite probe orbiting P9 would allow the possibility of detection and study of Hawking radiation, since the BH horizon would screen radiation from the CMB.…”

Evaporating primordial black holes, the string axiverse, and hot dark radiation

“…[27], two BHs can become gravitationally bound and decouple from the Hubble flow if their physical separation at matterradiation equality x < f 1/3 x, where x is the average BH separation at this redshift and f is the PBH fraction of the dark matter density. Given the existing constraints on f for BHs that are evaporating today from the contribution of Hawking radiation to the extra-galactic diffuse gamma-ray background, f 10 −7 [28,29], we conclude that only a small fraction of such BHs can become gravitationally bound and subsequently merge. Furthermore, mergers occurring early in the cosmic history will only affect the 'initial' conditions for the subsequent evolution driven essentially by evaporation.…”

“…(For related studies of modified PBH constraints in the context of extra-dimensional and other non-SM theories see [35][36][37][38][39].) We take f 0 ∼ 10 −7 to roughly saturate current bounds [28,29,33].…”

AlterBBN

“…In AlterBBN, the user can choose the heaviest elements to be considered for the calculation of the primordial abundances. This is particularly useful in the context of inhomogeneous BBN [15], where local baryon densities at BBN time can be much larger than in standard BBN.…”