Non-minimally Coupled Vector Boson Dark Matter

TL;DR

This paper explores a vector dark matter model with non-minimal coupling to gravity, analyzing its detection prospects and production mechanisms through freeze-out and freeze-in scenarios, and demonstrating viability over a wide parameter space.

Contribution

It introduces a simple abelian vector dark matter model with non-minimal gravitational coupling and studies its detection and production, including novel constraints on coupling strength and mass.

Findings

Detectable in direct detection experiments for certain coupling and mass ranges.

Freeze-in production can account for observed relic abundance with small coupling.

Graviton-mediated scattering can produce dark matter without non-minimal coupling.

Abstract

We consider a simple abelian vector dark matter (DM) model, where {\it only} the DM $(\widetilde{X}_\mu)$ couples non-minimally to the scalar curvature $(\widetilde{R})$ of the background spacetime via an operator of the form $\sim \widetilde{X}_\mu\,\widetilde{X}^\mu\,\widetilde{R}$. By considering the standard freeze-out scenario, we show, it is possible to probe such a non-minimally coupled DM in direct detection experiments for a coupling strength $\xi\sim\mathcal{O}\left(10^{30}\right)$ and DM mass $m_X\lesssim 55$ TeV, satisfying Planck observed relic abundance and perturbative unitarity. We also discuss DM production via freeze-in, governed by the non-minimal coupling, that requires $\xi\lesssim 10^{-5}$ to produce the observed DM abundance over a large range of DM mass depending on the choice of the reheating temperature. We further show, even in the absence of the non-minimal coupling, it is possible to produce the whole observed DM abundance via 2-to-2 scattering of the bath particles mediated by massless gravitons.