New Opportunities for Detecting Axion-Lepton Interactions

TL;DR

This paper revisits axion-like particles interacting with leptons, clarifies existing constraints, and identifies new detection opportunities through meson and W boson decays, impacting QCD axion research and experimental anomaly explanations.

Contribution

It introduces a new understanding of ALP interactions, distinguishing weak-violating and weak-preserving types, and proposes novel detection channels that expand current experimental searches.

Findings

New bounds on ALP parameter space affecting both ALP types.

Identification of decay processes as promising detection channels.

Implications for QCD axion models and experimental anomalies.

Abstract

We revisit the theory and constraints on axion-like particles (ALPs) interacting with leptons. We clarify some subtleties in the constraints on ALP parameter space and find several new opportunities for ALP detection. We identify a qualitative difference between weak-violating and weak-preserving ALPs, which dramatically change the current constraints due to possible "energy enhancements" in various processes. This new understanding leads to additional opportunities for ALP detection through charged meson decays (e.g., $\pi^+\to e^+ \nu a$, $K^+\to e^+ \nu a$) and $ W $ boson decays. The new bounds impact both weak-preserving and weak-violating ALPs and have implications for the QCD axion and addressing experimental anomalies using ALPs.