Axionlike Particles, Lepton-Flavor Violation, and a New Explanation of aμ and ae

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-flavornonuniversal or lepton-flavor-violating ALP couplings.

An explanation for the muon and electron g − 2 anomalies and dark matter

“…Therefore, the ten independent parameters in the scalar potential can be chosen as 17) and the quartic couplings λ 2,6,8 for the inert scalar fields.…”

“…Interestingly, this measurement also shows a possible disagreement between the data and theory, with the measured value lower than the SM prediction by JHEP09(2020)119 about 2.4σ [13]. These tantalizing opposite deviations have invited many studies to explore suitable NP models [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29].…”

Probing μτ flavor-violating solutions for the muon g − 2 anomaly at Belle II

“…Since the dipole operator requires the chirality flipping, one-loop correction involving a mediator with the µτ flavor violating couplings is enhanced by a factor of m τ /m µ O (10). Such µτ flavor violating scenarios are discussed to explain the muon g − 2 anomaly in the context of the axion like particles (ALPs) [11,12], in the general two Higgs doublet model (G2HDM) [13][14][15][16][17][18][19][20][21][22][23][24][25][26], and in the Z models [27][28][29][30]. Figure 1 shows the representative diagram to induce the δa µ contribution with a µτ flavor violating mediator particle X, which is either a scalar or vector boson, and the µτ flavor violating nature of X introduces the internal τ -propagator at one-loop level.…”

Electron and muon g−2 anomalies in general flavor conserving two-Higgs-doublet models

“…In particular, many popular models in which the anomaly scales with the square of the lepton mass [16] tend to generate too large δa e with the wrong sign. Some authors [17] argue that if the origin of both anomalies is beyond the SM, the corresponding model must incorporate some sort of effective decoupling between μ and e. Recent beyond-SM explanations of both anomalies can be found in [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]. A minimal extension of the SM is the two-Higgs-doublets model (2HDM) [33] which introduces, in general, a new set of flavor structures in the Yukawa sector.…”