Lepton number violation in top quark and neutralBmeson decays

Abstract

Lepton number violation (LNV) can be induced by Majorana neutrinos in four-body decays of the neutral B meson and the top quark. We study the effects of Majorana neutrinos in these |∆L| = 2 decays in an scenario where a single heavy neutrino can enhance the amplitude via the resonant mechanism. Using current bounds on heavy neutrino mixings, the most optimistic branching ratios turn out to be at the level of 10 −6 forB 0 → D + e − e − π + and t → bl + l + W − decays. Searches for these LNV decays at future facilities can provide complementary constraints on masses and mixings of Majorana neutrinos.

Searches for Majorana neutrinos inB−decays

“…A model dependent calculation of BðB À ! D 0 þ À À Þ can also be used to extract jV 4 j [10], but the þ À À mode is more sensitive. For the D ðÃÞþ À À channels upper limits cannot be extracted until there is a theoretical calculation of the hadronic form factor similar to those available for neutrinoless double decay.…”

“…2(c) we show how prolific semileptonic decays of the B À can result in the D 0 þ À À final state. This process has never been probed [10]. We benefit from the higher value of the Cabibbo-Kobayashi-Maskawa coupling jV cb j relative to jV ub j in the annihilation processes shown in Fig.…”

Lepton-number-violating four-body tau lepton decays

“…[38], the decay width À N varies between 10 À20 GeV and (at most) 10 À14 GeV for values of neutrino masses that are relevant for resonant À ! l À l À X þ decays.…”

“…Following the definitions given in Ref. [38], we can write the differential decay rate (in the rest frame of the decaying particle of mass M) in terms of five independent kinematical variables (see conventions in Fig. 2):…”

“…Very recently, we have reported the first calculation of the four-body decays B 0 ! D À l þ l þ À [38], which are expected to provide complementary constraints to the threebody decays of their charged counterparts. At higher energies, the production of same-sign dileptons at colliders [30,[39][40][41][42][43][44][45][46] and in top quark decays [38,47,48] has also been considered in the literature.…”