MUonE, muon g-2 and electroweak precision constraints within 2HDMs

Two Higgs doublet models (2HDMs) are attractive scenarios for physics beyond the Standard Model. In particular, lepton-specific manifestations remain contenders to explain the observed discrepancy between the anomalous magnetic moment of the muon ao predicted within the Standard Model and recent observations at Fermilab and BNL. Dominant uncertainties that affect ao have motivated the MUonE experiment to access the hadronic vacuum polarization contribution that impacts ao via elastic muon-electron scattering. In this work, we contrast the high precision that is achievable within the MUonE context with constraints from flavor physics, precision electroweak constraints and LHC searches as well as their extrapolations for a range of two Higgs doublet models with a softly broken Z2 symmetry. We find that the sensitivity of MUonE does not extend beyond the parameter regions that are already excluded by other constraints. MUonE will therefore provide a detailed measurement of the hadronic vacuum polarization contribution which then transparently informs ao interpretations in 2HDMs without modifications of correlations from beyond the Standard Model interactions. In passing we extend earlier results of LHC and flavor projections to lepton -specific 2HDM (Types X and Y) scenarios, and comment on the possibility of modifying the value of the W -boson mass; we briefly discuss the implications for a strong first-order electroweak phase transition for these models.

Automated summary

This work contrasts the high precision achievable within the MUonE experiment with constraints from flavor physics, precision electroweak constraints, and LHC searches for two Higgs doublet models. The study finds that MUonE's sensitivity does not extend beyond the parameter regions already excluded by other constraints. MUonE will provide a detailed measurement of the hadronic vacuum polarization contribution, informing interpretations of the anomalous magnetic moment in 2HDMs without modifications from beyond the Standard Model interactions.