Implications of the Muon g-2 result on the flavour structure of the lepton mass matrix

Abstract

The confirmation of the discrepancy with the Standard Model predictions in the anomalous magnetic moment by the Muon g-2 experiment at Fermilab points to a low scale of new physics. Flavour symmetries broken at low energies can account for this discrepancy but these models are much more restricted, as they would also generate off-diagonal entries in the dipole moment matrix. Therefore, if we assume that the observed discrepancy in the muon $$g-2$$ g - 2 is explained by the contributions of a low-energy flavor symmetry, lepton flavour violating processes can constrain the structure of the lepton mass matrices and therefore the flavour symmetries themselves predicting these structures. We apply these ideas to several discrete flavour symmetries popular in the leptonic sector, such as $$\Delta (27)$$ Δ ( 27 ) , $$A_4$$ A 4 , and $$A_5 < imes \mathrm{CP}$$ A 5 ⋉ CP .

Constraining Low-Scale Flavor Models with $\boldsymbol{(g-2)_μ}$ and Lepton Flavor Violation

“…We begin by briefly reviewing the idea introduced in Refs. [1,2] that the observed discrepancy in the anomalous magnetic moment of muon can be entirely explained by accounting for contributions from the breaking of a low-energy flavor symmetry. Such a framework works by exploiting the similar flavor structures present in the dipole matrix describing the anomalous magnetic moment, lepton flavor violating transitions and electric dipole moment, and the Yukawa matrix.…”

“…A framework, using effective operators, for how this could occur was given in Refs. [1,2]. There, the one-loop radiative corrections to the fermion masses, stemming from the breaking of a low-energy flavor symmetry, also generated the dipole matrices.…”

“…In this work, we follow up on the ideas explored by some of the authors in Refs. [1,2] by providing explicit constructions of flavor models capable of realizing these ideas. As a proof of concept, we build two explicit models with low-energy flavor symmetries based on the groups T 13 and A 5 , capable of explaining the muon g − 2 discrepancy while satisfying all constraints from LFV dipole transitions.…”

“…In Section 2, we review the salient features of the framework proposed in Refs. [1,2] for constraining low-scale flavor models using the anomalous magnetic moment of the muon and LFV observables in the language of effective field theories (EFT). Sections 3 and 4 contain the main results of this work: explicit constructions of low-scale flavor models based on the flavor groups T 13 and A 5 capable of producing sizable contributions to the muons anomalous magnetic moment while evading LFV constraints.…”

“…Following Ref. [2], we can assume that the entries of the dipole matrix are of the order of the corresponding entries of the Yukawa matrix in the flavor basis, C κ…”