Refined Low-Energy Supernova Constraints on Lepton Flavor Violating Axions

TL;DR

This paper refines constraints on lepton-flavor-violating axions using low-energy supernovae, considering multiple production channels and calculating energy transfer and loss, resulting in the most stringent bounds for certain ALP masses.

Contribution

It introduces new calculations of semi-Compton scattering for LFV-ALPs and refines supernova constraints by including detailed energy transfer and loss mechanisms.

Findings

LESNe provide the most stringent constraints for ALP masses above ~110 MeV.

Semi-Compton scattering is significant in the intermediate-mass range.

Refined bounds strengthen previous supernova limits on LFV axions.

Abstract

The supernova (SN) core, characterized by its extreme temperature and density, serves as a unique laboratory for new-physics searches. Low-energy supernovae (LESNe) provide particularly powerful probes, as their low explosion energies place stringent limits on any additional energy deposition in the mantle by new particles. We present refined LESN constraints on lepton-flavor-violating (LFV) axions and axion-like particles (ALPs) with electron-muon couplings. We consider four production channels in the SN: muon decay, lepton bremsstrahlung, electron-muon coalescence, and semi-Compton scattering, the last of which is investigated here for the first time in the context of LFV-ALPs. We find that muon decay dominates in the low-mass regime, electron-muon coalescence in the high-mass regime, and semi-Compton scattering in the intermediate-mass range. To derive accurate limits, we compute both the energy transfer from the SN core to the mantle and the energy loss due to ALP production in the mantle, which can be substantial for both large and small couplings -- the latter case, to our knowledge, not previously noted in the literature. We find that LESNe provide the most stringent constraints on the parameter space for ALP masses above $\sim 110$ MeV. These refined results strengthen previous SN bounds and highlight the exceptional sensitivity of LESNe to LFV new physics.