Constraints on lepton-flavor mixing with third-generation new physics
Abstract
We study the implications of an approximate $U(2)^5$ flavor symmetry at the TeV scale, under the assumption of new physics predominantly coupled to the third-generation fermions, focusing on the breaking of the $U(2)_\ell$ subgroup governing the mixing between second- and third-generation left-handed leptons. We derive constraints on the corresponding spurion parameter $δ$ from current data on lepton flavor violating (LFV) and lepton flavor universality (LFU) observables, finding that $R_{K^{(*)}}$ and $\mathcal{B}(B_s \to μμ)$ give the most stringent bound on $δ$, yielding ${|δ|
Fields of Study & Subjects
Particle physics theoretical and experimental studies
Neutrino Physics Research
Particle Detector Development and Performance
Publication details
- Journal / source
- Physics Letters B
- Publisher
- Elsevier BV
- Volume
- 879
- Pages
- 140582–140582
- Publication date
- 22 May 2026
- Language
- EN