Primordial Black Hole Formation in a Double Inflation Model in Supergravity

TL;DR

This paper investigates a supergravity-based double inflation scenario consisting of a pre-inflation hybrid stage followed by a new inflation. The model yields a strongly scale-dependent density spectrum: large fluctuations on small scales and suppressed fluctuations on large scales, enabling the formation of primordial black holes around one solar mass. The authors derive the conditions under which ~1 M_sun PBHs can form in a parameter window that also satisfies gravitino and COBE constraints, proposing these PBHs as MACHO candidates. They further note the potential for gravitational wave signals from PBH binaries if such black holes dominate dark matter, and discuss how relaxing certain SUSY-breaking–inflation-scale relations could widen the viable parameter space.

Abstract

It has been recently pointed out that the initial value problem in new inflation models is naturally solved by supergravity effects if there exists a pre-inflation before the new inflation. We study this double inflation model in details and find that density fluctuations on small cosmological scales are much larger than those on large scales due to peculiar property of the new inflation. We show that this results in production of primordial black holes which have $\sim 1 M_{\odot}$ masses in a certain parameter region of the double inflation model. We stress that these black holes may be identified with MACHOs observed in the halo of our galaxy.