Primordial black holes generated by fast-roll mechanism in non-canonical natural inflation

TL;DR

This paper introduces a fast-roll mechanism in non-canonical natural inflation to generate primordial black holes and gravitational waves, explaining dark matter and matching recent observational data.

Contribution

It proposes a novel fast-roll process in non-canonical inflation that produces PBHs and GWs consistent with various astrophysical observations.

Findings

PBHs can account for dark matter, microlensing, LIGO-VIRGO, and NANOGrav signals.

The GW spectrum fits NANOGrav 15-year data with a specific spectral index.

PBHs form during the radiation-dominated era, compatible with cosmological constraints.

Abstract

In this work, a new fast-roll (FR) mechanism to generate primordial black holes (PBHs) and gravitational waves (GWs) in generalized non-canonical natural inflation is introduced. In this model, choosing a suitable function for non-canonical mass scale parameter $M(\phi)$ gives rise to produce a cliff-like region in the field evolution path. When inflaton rolls down the steep cliff, its kinetic energy during a FR stage increases in comparison with a slow-roll (SR) stage. Hence, seeds of PBH production are born in this transient FR stage. Depending on the position of the cliff, appropriate cases of PBHs for explaining total dark matter (DM), microlensing effects, LIGO-VIRGO events and NANOGrav 15 year data can be formed. The density spectrum of GWs related to one case of the model lies in the NANOGrav 15 year domain and behaves like $\Omega_{\rm GW_0}\sim f^{5-\gamma}$. The spectral index $\gamma=3.42$ for this case satisfies the NANOGrav 15 year constraint. Moreover, regarding reheating considerations, it is demonstrated that PBHs are born in the radiation-dominated (RD) era. Furthermore, viability of the model in light of theoretical swampland criteria and observational constraints on cosmic microwave background (CMB) scales are illustrated.