Regular Article - Theoretical Physics

Flavor violating leptonic decays of and leptons in the Standard Model with massive neutrinos

¹ Departamento de Física, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Apdo. Postal 14-740, 07000, México, D.F., Mexico
² CAFPE and Departamento de Física Teórica y del Cosmos, Universidad de Granada, E-18071, Granada, Spain

^* e-mail: ghernandez@fis.cinvestav.mx
^** e-mail: ghernandezt@correo.ugr.es

Received: 23 October 2018
Accepted: 27 December 2018
Published online: 29 January 2019

Abstract

We have revisited the computations of the flavor violating leptonic decays of the and 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 () decays (Pham, Eur Phys J C 8:513 1999), which was at odds with the corresponding predictions for the 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.