Abstract
Axionlike particles (ALPs) with lepton-flavor-violating couplings can be probed in exotic muon and tau decays. The sensitivity of different experiments depends strongly on the ALP mass and its couplings to leptons and photons. For ALPs that can be resonantly produced, the sensitivity of three-body decays such as μ→3e and τ→3μ exceeds by many orders of magnitude that of radiative decays like μ→eγ and τ→μγ. Searches for these two types of processes are therefore highly complementary. We discuss experimental constraints on ALPs with a single dominant lepton-flavor-violating coupling. Allowing for one or more such couplings offers qualitatively new ways to explain the anomalies related to the magnetic moments of the muon or the electron. The explanation of both anomalies requires lepton-flavor-nonuniversal or lepton-flavor-violating ALP couplings.
Highlights
Introduction.—Axionlike particles (ALPs) can be the low-energy remnants of an ultraviolet (UV) extension of the standard model (SM) with a spontaneously broken approximate global symmetry [1]
The UV theory could even be responsible for the breaking of the SM flavor symmetries, in which case the ALPs are known as flavons [8,9,10,11,12]
In Ref. [28], it was shown how this expectation can break down for light new physics, and, in this Letter, we explore the far-reaching implications for the sensitivity of experiments searching for ALPs
Summary
Introduction.—Axionlike particles (ALPs) can be the low-energy remnants of an ultraviolet (UV) extension of the standard model (SM) with a spontaneously broken approximate global symmetry [1]. Axionlike particles (ALPs) with lepton-flavor-violating couplings can be probed in exotic muon and tau decays. The sensitivity of different experiments depends strongly on the ALP mass and its couplings to leptons and photons.
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