2018/07/31 by G. Hernández-Tomé, G. López Castro, P. Roig · 2 citations
Physics and Astronomy · #hep-ph #hep-ex
paper · pdf · doi:10.1140/epjc/s10052-019-6563-4
published as Eur. Phys. J. C (2019) 79:84 Eur. Phys. J. C (2020) 80: 438 · 24 pages, 3 Figures, a new evaluation of the Branching fractions and new appendix added, main conclusion remains unchanged, some typos corrected
arxiv created 2018/09/10 · arxiv updated 2020/05/29
We have revisited the computations of the flavor violating leptonic decays of the τ and μ leptons into three lighter charged leptons in the Standard Model with non-vanishing neutrino masses. We were driven by a claimed unnaturally large branching ratio predicted for the τ-→ μ- ℓ+ ℓ- (ℓ=μ, e) decays \citePham:1998fq, which was at odds with the corresponding predictions for the μ-→ e- e-e+ processes \citePetcov:1976ff. In contrast with the prediction in \citePham:1998fq, our results are strongly suppressed and in good agreement with the approximation done in ref.~\citePetcov:1976ff, where masses and momenta of the external particles were neglected in order to deal with the loop integrals. However, as a result of keeping external momenta and masses in the computation of the dominant penguin and box diagrams- we even find slightly smaller branching fractions. Therefore, we confirm that any future observation of such processes would be an unambiguous manifestation of new physics beyond the Standard Model