Lepton-Flavoured Scalar Dark Matter in Dark Minimal Flavour Violation

Abstract

We study a simplified model of lepton-flavoured complex scalar dark matter set up in the Dark Minimal Flavour Violation framework. In this model the Standard Model is extended by a scalar dark matter flavour triplet and a charged fermionic mediator, through which dark matter couples to the right-handed charged leptons of the Standard Model. This interaction is parameterized by a new $3\times 3$ coupling matrix $\lambda$. Consistent with the field content of the model, also the Standard Model's approximate flavour symmetry is extended to include an additional global $U(3)$ associated with the dark matter flavour triplet. In addition to the Standard Model Yukawa couplings, the new coupling matrix $\lambda$ is assumed to constitute the only source that violates this extended symmetry. We analyse the parameter space of this model by investigating constraints from collider searches, lepton flavour violating decays, the observed dark matter relic density, and direct as well as indirect dark matter detection experiments. By performing a combined analysis of all constraints we find that restrictions from lepton flavour violating decays, the observed relic density and dark matter nucleon scattering are dominant. The combination of the latter two renders limits from collider searches irrelevant while indirect detection constraints are weak due to a $p$-wave suppression of the annihilation rate. We conclude that lepton-flavoured scalar dark matter has a rich phenomenology and is a viable dark matter candidate.