New Thermal Relic Targets for Inelastic Vector-Portal Dark Matter

TL;DR

This paper explores a specific inelastic dark matter model with a dark photon, identifying parameter regions that evade current constraints and are promising for future experimental searches, while also affecting small-scale cosmic structures.

Contribution

It provides a detailed analysis of the forbidden dark matter regime with inelastic interactions, including updated constraints and viable parameter space for future detection.

Findings

Relaxed CMB and self-interaction constraints compared to symmetric DM.

Identified parameter space suitable for accelerator searches.

Predicted self-interaction cross sections impacting small-scale structure.

Abstract

We examine the vector-portal inelastic dark matter (DM) model with DM mass $m_\chi$ and dark photon mass $m_{A'}$, in the `forbidden dark matter' regime where $1 \lesssim m_{A'}/m_\chi \lesssim 2$, carefully tracking the dark sector temperature throughout freezeout. The inelastic nature of the dark sector relaxes the stringent cosmic microwave background (CMB) and self-interaction constraints compared to symmetric DM models. We determine the CMB limits on both annihilations involving excited states and annihilation into $e^+e^-$ through initial-state-radiation of an $A'$, as well as limits on the DM self-scattering, which proceeds at the one-loop level. The unconstrained parameter space serves as an ideal target for accelerator $A'$ searches, and provides a DM self-interaction cross section that is large enough to observably impact small-scale structure.