  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.
