Testing freeze-in with axial and vector $Z'$ bosons

TL;DR

This paper investigates the production and detection of feebly interacting dark matter particles via a $Z'$ portal with both vector and axial couplings, exploring experimental bounds across a wide mass range from MeV to PeV.

Contribution

It provides a comprehensive analysis of $Z'$ portal FIMP dark matter, including bounds from various experiments and the impact of axial couplings, extending the phenomenological understanding of these models.

Findings

FIMPs can be tested by multiple experiments in a complementary manner.

WIMPs remain viable in the low $Z'$ mass and resonance regions.

Axial couplings significantly influence the experimental constraints.

Abstract

The freeze-in production of Feebly Interacting Massive Particle (FIMP) dark matter in the early universe is an appealing alternative to the well-known - and constrained - Weakly Interacting Massive Particle (WIMP) paradigm. Although challenging, the phenomenology of FIMP dark matter has been receiving growing attention and is possible in a few scenarios. In this work, we contribute to this endeavor by considering a $Z^\prime$ portal to fermionic dark matter, with the $Z^\prime$ having both vector and axial couplings and a mass ranging from MeV up to PeV. We evaluate the bounds on both freeze-in and freeze-out from direct detection, atomic parity violation, leptonic anomalous magnetic moments, neutrino-electron scattering, collider, and beam dump experiments. We show that FIMPs can already be tested by most of these experiments in a complementary way, whereas WIMPs are especially viable in the $Z^\prime$ low mass regime, in addition to the $Z^\prime$ resonance region. We also discuss the role of the axial couplings of $Z^\prime$ in our results. We therefore hope to motivate specific realizations of this model in the context of FIMPs, as well as searches for these elusive dark matter candidates.