New Parity-Violating Muonic Forces

TL;DR

This paper proposes models with gauged right-handed muon number to explain the proton radius discrepancy, predicting enhanced parity-violating asymmetries in muon-nucleus scattering that can be tested with current experiments.

Contribution

It introduces a new class of models with light vector and scalar forces specific to muons, explaining the proton radius puzzle and suggesting observable parity violation effects.

Findings

Models with gauged muon number are consistent with observations.

Predicted parity-violating asymmetries are significantly enhanced.

Potential for new experimental tests with existing muon beams.

Abstract

The recent discrepancy between proton charge radius measurements extracted from electron-proton versus muon-proton systems is suggestive of a new force that differentiates between lepton species. We identify a class of models with gauged right-handed muon number, which contains new vector and scalar force carriers at the 100 MeV scale or lighter, that is consistent with observations. Such forces would lead to an enhancement by several orders-of-magnitude of the parity-violating asymmetries in the scattering of low-energy muons on nuclei. The relatively large size of such asymmetries, O(10^{-4}), opens up the possibility for new tests of parity violation in neutral currents with existing low-energy muon beams.