  This study investigates the classical Higgs inflation model with a modified
Higgs potential featuring a dip. We examine the implications of this
modification on the generation of curvature perturbations, stochastic
gravitational wave production, and the potential formation of primordial black
holes (PBHs). Unlike the classical model, the modified potential allows for
enhanced power spectra and the existence of PBHs within a wide mass range
$1.5\times10^{20}$ g -- $9.72\times10^{32}$ g. We identify parameter space
regions that align with inflationary constraints and have the potential to
contribute significantly to the observed dark matter content. Additionally, the
study explores the consistency of the obtained parameter space with
cosmological constraints and discusses the implications for explaining the
observed excess in gravitational wave signals, particularly in the NANOGrav
experiment. Overall, this investigation highlights the relevance of the
modified Higgs potential in the classical Higgs inflation model, shedding light
on the formation of PBHs, the nature of dark matter, and the connection to
gravitational wave observations.
