Low-reheating scenario in dark Higgs inflation and its impact on dark photon dark matter production

TL;DR

This paper explores a dark Higgs inflation model with a dark photon as dark matter, analyzing low-reheating scenarios that align with observational data and offer potential detection prospects.

Contribution

It introduces a unified dark Higgs inflation framework with detailed phenomenology, including entropy dilution effects on dark photon dark matter and compatibility with cosmological constraints.

Findings

Dark Higgs inflation predicts spectral index and tensor-to-scalar ratio consistent with Planck and BICEP/Keck data.

Low reheating temperatures as low as 1 MeV are achievable, enhancing detection prospects.

Entropy dilution allows for stronger dark photon couplings while maintaining correct relic abundance.

Abstract

We investigate dark matter (DM) phenomenology and cosmic inflation within a unified framework based on a dark $U(1)_D$ gauge extension of the Standard Model (SM). The associated dark gauge boson, namely the dark photon, serves as a viable DM candidate, which we call dark photon dark matter (DPDM), whilst the dark Higgs field drives inflation. We explore a low-reheating scenario where DM production occurs during reheating, resulting in significant entropy dilution of the DPDM abundance. Both weakly interacting massive particle (WIMP) and feebly interacting massive particle (FIMP) DM scenarios are explored, depending on the dark gauge coupling strength. For FIMP-type DM, the entropy dilution allows for stronger couplings whilst maintaining the correct relic abundance, potentially bringing these candidates within the reach of current and near-future detection experiments. Similarly, WIMP-type DM can be realised with weaker couplings. We perform a comprehensive parameter scan incorporating constraints from collider data, DM direct and indirect detection experiments, and cosmological observations. Taking quantum corrections and running of the couplings into account, we demonstrate that dark Higgs inflation yields predictions for the spectral index $n_s$ and the tensor-to-scalar ratio $r$ that are consistent with the Planck, BICEP/Keck, and ACT data. The nonminimal coupling of the dark Higgs inflaton field to gravity is shown to be much smaller than in the case of the SM Higgs inflation scenario, avoiding unitarity concerns. We show that reheating temperatures as low as 1 GeV and 1 MeV can be achieved through the decay and scattering processes of the inflaton, respectively, with the latter allowing for larger Higgs mixing angles and enhanced detection prospects. Our results establish that this minimal extension successfully unifies DM physics with inflationary cosmology.