The Stochastic Gravitational-Wave Background from Primordial Black Holes in R-Symmetric $SU(5)$ Inflation

TL;DR

This paper investigates how primordial black holes formed during R-symmetric $SU(5)$ inflation could account for dark matter and produce detectable gravitational waves, while also exploring implications for proton decay.

Contribution

It demonstrates a model where inflation leads to primordial black holes as dark matter and predicts observable gravitational waves and proton decay signals.

Findings

Primordial black holes can account for all dark matter.

Scalar induced gravitational waves are detectable with current/future detectors.

Inflationary parameters are consistent with Planck data and gauge unification.

Abstract

This study explores the realization of nonminimally coupled Higgs inflation in the context of no-scale supergravity, investigates the formation of primordial black holes, and examines the potential for observable proton decay within the framework of the R-symmetric $SU(5)$ model. For inflation, both single and multifield scenarios are investigated. The prediction of the single-field model for the tensor-to-scalar ratio, $r$, is approximately $10^{-3}$, and the scalar spectral index falls within Plank's 1$\sigma$ range. The running of the scalar spectral index, $-{dn_{s}}/{d\ln{k}}$, is approximately $10^{-4}$. A realistic scenario of reheating and non-thermal leptogenesis is employed with reheat temperature $T_r\sim10^9$ GeV. In the multifield case, we mainly focus on Primordial Black Holes (PBHs) and Gravitational Waves (GWs). In this inflationary framework, we demonstrate how a suitable choice of parameters can result in an enhanced scalar power spectrum, leading to the production of primordial black holes (PBHs) capable of fully accounting for dark matter. We also show that this scenario leads to Scalar Induced Gravitational Waves (SIGW) which can be detected in current and future GW detectors. We explore different proton decay channels to look for observable predictions for the next-generation proton decay experiments Hyper-K and DUNE consistent with gauge coupling unification and cosmological bounds.