We revisit the theory and constraints on axionlike 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.

• Received 12 September 2022
• Revised 27 March 2023
• Accepted 10 May 2023

DOI:https://doi.org/10.1103/PhysRevLett.130.241801

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Published by the American Physical Society