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

TL;DR

This paper evaluates the MUonE experiment's ability to constrain two Higgs doublet models (2HDMs) in the context of muon g-2 anomalies, comparing its sensitivity with existing experimental bounds and discussing implications for electroweak physics.

Contribution

It provides a comprehensive analysis of MUonE's potential to inform 2HDM parameter space and extends previous LHC and flavor physics projections to lepton-specific 2HDMs, including implications for electroweak phase transition.

Findings

MUonE's sensitivity does not surpass existing constraints.

MUonE will precisely measure hadronic vacuum polarisation, aiding muon g-2 interpretations.

Extensions to lepton-specific 2HDMs and implications for W-boson mass are discussed.

Abstract

Two Higgs doublet models 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 $a_\mu$ predicted within the Standard Model and recent observations at Fermilab and BNL. Dominant uncertainties that affect $a_\mu$ have motivated the MUonE experiment to access the hadronic vacuum polarisation contribution that impacts $a_\mu$ via elastic muon-electron scattering. In this work, we contrast the high precision that is achievable within the MUonE context with constraints from flavour physics, precision electroweak constraints and LHC searches as well as their extrapolations for a range of two Higgs doublet models with a softly broken $\mathbb{Z}_2$ 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 polarisation contribution which then transparently informs $a_\mu$ interpretations in 2HDMs without modifications of correlations from beyond the Standard Model interactions. In passing we extend earlier results of LHC and flavour 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.