Opening the Parameter Space of sub-GeV Inelastic Dark Matter through Parity Violation

TL;DR

This paper explores how parity violation in inelastic sub-GeV dark matter models can relax experimental constraints, expanding the viable parameter space and highlighting the potential of upcoming experiments like LDMX.

Contribution

It introduces a framework to analyze parity-violating effects in inelastic dark matter models, showing how these effects can open new parameter space regions.

Findings

Parity violation induces small diagonal couplings in inelastic DM models.

Revised abundance calculations expand the allowed parameter space.

Upcoming LDMX experiment will probe significant regions of this space.

Abstract

Sub-GeV dark matter (DM) has emerged as a particularly compelling target in light of the persistent null results from conventional DM searches. While s-wave annihilating DM candidates with masses below the GeV are strongly constrained by indirect-detection bounds, inelastic scenarios can naturally evade these limits. In this work, we show that parity violation can play an important role in inelastic DM models featuring long-lived excited states by inducing small diagonal couplings that significantly relax experimental constraints. A precise determination of the excited-state abundance is essential for assessing the phenomenology of such models. To this end, we solve the integrated Boltzmann equation, fully accounting for up- and down-scattering with electrons and positrons as well as dark-sector conversion processes. Using the resulting abundance, we update the viable parameter space in light of the most recent experimental constraints and demonstrate that parity-violating interactions can reopen broad regions of parameter space that would otherwise be excluded. Moreover, the forthcoming LDMX experiment will probe a significant portion of the parameter space. The framework developed in this work can be readily applied to other exothermic sub-GeV DM scenarios.