New directions in inelastic Dark Matter - The Role of Parity in Dark Sectors

Dark matter remains one of the most pressing and enigmatic challenges in fundamental physics. Despite overwhelming gravitational evidence for its existence, its identity and particle properties remain unknown. Among the most promising frameworks explaining dark matter are \textit{thermal relic scenarios}, in which dark matter was once in equilibrium with the Standard Model plasma. Their attractiveness relies on their predictivity and independence from the initial conditions of the universe. Within this class, \textit{inelastic dark matter} offers a minimal and flexible setup that naturally evades stringent bounds from direct and indirect detection experiments while predicting rich experimental signatures, particularly at particle colliders.

This thesis explores a generalization of inelastic dark matter that lifts the often-unquestioned assumption of parity conservation in the hidden sector. We develop a framework called \emph{not-so-inelastic dark matter}, which smoothly interpolates between inelastic and Majorana dark matter models and involves two mediators: a dark photon and a dark Higgs boson. We show that parity violation in this context enables novel decay channels, allows for large mass splittings, and introduces distinctive di-decay signatures that can be observed at intensity frontier experiments. ... mehrIt further gives rise to a minimal scalar-mediated variant, referred to as \emph{minimal-inelastic dark matter}, offering predictive signals for direct detection experiments.

Through detailed theoretical and phenomenological analysis, we identify viable regions of parameter space that are consistent with thermal freeze-out and current experimental limits. Moreover, large portions of the viable parameter space are expected to be probed by ongoing experiments such as Belle~II, NA64, and NA62, as well as by future detectors like DARWIN. Our results suggest that combining multiple collider observables---especially \textit{di-decay signatures}---can enable reconstruction of the coupling structure, or ``flavor structure'', of dark matter in these models. In particular, our work highlights the complementarity between direct detection, collider searches, and cosmological probes in exploring the {not-so-inelastic dark matter} framework. This work not only broadens the scope of viable thermal dark matter scenarios but also motivates a re-evaluation of discrete symmetries---particularly \textit{parity}---in the construction of dark sector theories.