Nonstandard Thermal History and Formation of Primordial Black Holes and SIGWs in Einstein–Gauss–Bonnet Gravity

Abstract

In this article, we examine the formation of primordial black holes (PBHs) in the mutated hilltop inflation model coupled with the Einstein–Gauss–Bonnet term. A suitable choice of the coupling function can produce the ultra-slow-roll (USR) regime during the inflationary phase, which lasts for some number of e-folds leading to a significant enhancement to the curvature power spectrum for small scales so that it grows up to the order of ; a crucial feature for producing PBH and scalar-induced gravitational waves (SIGWs). We investigate the formation of PBHs for different sets of parameters. The presented model is capable of producing PBH in a wide range of mass, from to . PBHs with mass can account for the microlensing event in Optical Gravitational Lensing Experiment as well as the asteroid masses ; PBH can be attributed to 100% of the dark matter present in the Universe. Whereas PBHs in the mass range are compatible with LIGO-Virgo data. Our investigation is generalized to include the effect of nonstandard thermal history with an equation of state 1/3 < ω ≤ 1 on PBHs, and it is shown that this possibility can severely impact the formation and abundance of PBHs. The enhancement of the scalar power spectrum also leads to the SIGWs. It is realized that, by increasing ω, there is a slight enhancement of the SIGWs. Moreover, produced SIGWs are well within the detectable frequency ranges of current and future detectors.