Flavoured $(g-2)_μ$ with Dark Lepton Seasoning

Abstract: As a joint explanation for the dark matter (DM) problem and the muon $(g-2)$ anomaly, we propose a simplified model of lepton-flavoured complex scalar DM with couplings to both the left- and right-handed leptons of the Standard Model (SM). Both interactions are governed by the same new flavour-violating coupling matrix $\lambda$, however we allow for a relative scaling of the coupling strength. The SM is further extended by two fermion representations, transforming as an $SU(2)L$ doublet and singlet, respectively, and mediating these interactions. The fermions additionally couple to the SM Higgs doublet via a new Yukawa coupling. To study the model's phenomenology we first investigate constraints from collider searches, flavour experiments, precision tests of the SM, the DM relic density, and direct as well as indirect detection experiments individually. We then perform a combined analysis by demanding that all mentioned constraints are satisfied simultaneously. We use the results of this combined analysis and examine if the model is capable of accommodating the $(g-2)\mu$ anomaly within its viable parameter space without introducing fine-tuned lepton masses. For all benchmark scenarios we consider, we find that the central value of $\Delta a_\mu^\text{exp}$ can be reached without generating too large corrections to the lepton masses. We hence conclude that this model qualifies as a viable and attractive lepton-flavoured DM model that at the same time solves the $(g-2)_\mu$ anomaly.