Ellipse of Muon Dipole Moments

We show that any new interaction resulting in a chirally enhanced contribution to the muon magnetic moment necessarily modifies the decay rate of the Higgs boson to muon pairs or generates the muon electric dipole moment. These three observables are highly correlated, and near future measurements of h→μ^{+}μ^{-} will carve an ellipse in the plane of dipole moments for any such model. Together with the future measurements of the electric dipole moment many models able to explain the muon g-2 anomaly can be efficiently tested.

Simplest and Most Predictive Model of Muon g-2 and Thermal Dark Matter

The long-standing 4.2σ muon g-2 anomaly may be the result of a new particle species which could also couple to dark matter and mediate its annihilations in the early Universe. In models where both muons and dark matter carry equal charges under a U(1)_{L_{μ}-L_{τ}} gauge symmetry, the corresponding Z^{'} can both resolve the observed g-2 anomaly and yield an acceptable dark matter relic abundance, relying on annihilations which take place through the Z^{'} resonance. Once the value of (g-2)_{μ} and the dark matter abundance are each fixed, there is very little remaining freedom in this model, making it highly predictive. We provide a comprehensive analysis of this scenario, identifying a viable range of dark matter masses between approximately 10 and 100 MeV, which falls entirely within the projected sensitivity of several accelerator-based experiments, including NA62, NA64μ, M^{3}, and DUNE. Furthermore, portions of this mass range predict contributions to ΔN_{eff} which could ameliorate the tension between early and late time measurements of the Hubble constant, and which could be tested by stage 4 CMB experiments.