Flavor violating leptonic decays of $$\tau $$ τ and $$\mu $$ μ leptons in the Standard Model with massive neutrinos

Autor: G. Hernández-Tomé, G. López Castro, P. Roig
Jazyk: angličtina
Rok vydání: 2019
Předmět:
Zdroj: European Physical Journal C: Particles and Fields, Vol 79, Iss 1, Pp 1-16 (2019)
Druh dokumentu: article
ISSN: 1434-6044
1434-6052
DOI: 10.1140/epjc/s10052-019-6563-4
Popis: Abstract We have revisited the computations of the flavor violating leptonic decays of the $$\tau $$ τ and $$\mu $$ μ leptons into three lighter charged leptons in the Standard Model with massive neutrinos. We were driven by a claimed unnaturally large branching ratio predicted for the $$\tau ^-\rightarrow \mu ^- \ell ^+ \ell ^-$$ τ-→μ-ℓ+ℓ- ($$\ell =\mu , e$$ ℓ=μ,e ) decays (Pham, Eur Phys J C 8:513 1999), which was at odds with the corresponding predictions for the $$\mu ^-\rightarrow e^- e^-e^+$$ μ-→e-e-e+ processes (Petcov, Sov J Nucl Phys 25:340 1977). In contrast with the prediction in [17], our results are strongly suppressed and in good agreement with the approximation made in Ref. [15], 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.
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