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

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.