Minimal dark matter model for muon g−2 with scalar lepton partners up to the TeV scale

Abstract

The E989 experiment at the Fermi National Laboratory reported a $4.2\ensuremath{\sigma}$ discrepancy between the measured magnetic dipole moment of the muon, and its prediction in the Standard Model (SM). In this study, we address the anomaly by considering a minimal and generic extension to the SM which also provides for a dark matter (DM) candidate. The extra states in this framework are: a SM singlet Majorana fermion, referred to as the Bino, playing the role of DM; and muonic scalars, referred to as sleptons. The couplings between the sleptons, SM muons and the Bino can account for the muon $g\ensuremath{-}2$ anomaly if the scalar muon partners, or smuons, mix chirality. On the other hand, the DM relic density is satisfied primarily through coannihilation effects involving the Bino and the lighter sleptons. The viable parameter space of our model includes regions with relatively light coannihilating particles, similar to what has been found in previous scans of the Minimal Supersymmetric Standard Model (MSSM). Relaxing the assumption of minimal flavor violation typically assumed in the MSSM, we see that scenarios with sizable smuon mixing and large mass splittings between the smuons can satisfy both the muon $g\ensuremath{-}2$ anomaly and the DM relic density for coannihilating particle masses up to and beyond the TeV scale. When we specify the origin of the left-right smuon mixing to be trilinear couplings between the smuons and the SM Higgs boson, the constraints on these scenarios arising from perturbative unitarity and electroweak vacuum stability confine the coannihilating particle masses to be $\ensuremath{\lesssim}1\text{ }\text{ }\mathrm{TeV}$. We demonstrate that next generation direct detection experiments are only marginally sensitive to the viable parameter space of our model, and, thus, a future lepton collider could be the essential probe necessary to distinguish our model from other solutions to the muon $g\ensuremath{-}2$ anomaly which involve extra states beyond the SM.