Dark Photon mediated Inelastic Dark Matter in Cosmology, Astrophysics and Colliders

TL;DR

This paper systematically explores the phenomenology of dark photon mediated inelastic dark matter, analyzing its parameter space and potential signals in cosmology, astrophysics, and collider experiments, especially focusing on LHC LLP searches.

Contribution

It provides a comprehensive parameter scan of the A' iDM model fixing certain couplings and assesses its detectability in current and future experiments, expanding beyond previous benchmark studies.

Findings

Dark photon mediated iDM is compatible with current constraints.

FASER can probe or exclude significant parameter regions for light dark matter.

Parameter space overlaps with neutron star capture signals.

Abstract

We provide a systematic discussion of the phenomenology of Dark Photon iDM (A$^{\prime}$iDM) where the Standard Model (SM) is extended by a dark sector containing an additional $U(1)_D$ gauge symmetry under which all SM particles are neutral, and that couples to the SM hypercharge gauge boson through a kinetic mixing parameter $\epsilon$. The model contains two Majorana states $\chi_1$ and $\chi_2$ with $\delta=M_{\chi_2}-M_{\chi_1}>0$ and $\chi_1$ the dark matter candidate, and a dark photon $A^{\prime}$ with mass $M_{A^{\prime}}$. Our analysis represents an integration of existing ones, where only specific benchmarks of the A$^{\prime}$iDM scenario have been discussed. In particular, we fix the $U(1)_D$ coupling $\alpha_D$ equal to the electromagnetic one $\alpha_{EM}$ and $\epsilon$ to its experimental upper bound, and perform a complete scan of the remaining parameters $(M_{\chi_1},\delta, M_{A^{\prime}})$, discussing the $\chi_1$ relic abundance, its direct and indirect searches, as well as potential signals from astrophysics and accelerators. Our systematic scan shows that $\alpha_D$ = $\alpha_{EM}$ is not disfavored, as some previous analyses, limited to specific benchmarks, may suggest. We also find that when the $\chi_1$ relic density matches observation direct and indirect searches are not kinematically accessible. On the other hand we find that the projected luminosity of FASER, a detector searching for Long Lived Particles (LLP) decay at the LHC, can probe or rule out the parameters space of the model for $M_{\chi_1}\lesssim$ 7 GeV, 100 MeV $\lesssim \delta\lesssim$ 300 MeV and $M_{A^{\prime}}\lesssim$ 25 GeV. This range of parameter could be significantly extended by the FASER 2 upgrade proposed for the High-Luminosity phase at the LHC. The parameter space probed by LLP seaches partially overlaps with that probed by $\chi_1$ capture in neutron stars.