Majorana neutrinos with effective interactions in B decays

Abstract

We investigate the possible contribution of Majorana neutrinos to B meson decays in an effective interaction formalism, in the mass range 0.5 GeV < m N < 5 GeV. We study the decay of the B − meson via B − → µ − µ − π + at LHCb, which is a signal for leptonic number violation and the presence of Majorana neutrinos, and put bounds on different new physics contributions, characterized by their Dirac-Lorentz structure. We also study the bounds imposed by the radiative B decay (B − → µ − νγ) results from Belle. The obtained bounds are more restrictive than previous values found for dimension 6 four-fermion contact vectorial and scalar Majorana neutrino interactions in the context of the Left-Right symmetric model for higher Majorana masses at the LHC, showing that the direct calculation of the effective N interactions contribution to different processes can help to put more stringent bounds to different UV-complete models parameterized by an effective Lagrangian.where n is the mass dimension of the operator O (n) J . Note that we do not include the Type-I seesaw Lagrangian terms giving the Majorana and Yukawa terms for the sterile neutrinos. The dominating effects come from the lower dimension operators that can be generated at tree level in the unknown underlying renormalizable theory.

Angular and polarization observables for Majorana-mediated B decays with effective interactions

“…The sets 4, 5 and 6 discard this contribution. The total N width is around three orders of magnitude higher in the sets 1, 2 and 3 than in the sets 4, 5 and 6 [55].…”

“…The minimum value of E γ in Fig. 4a for each m N is the value where the effective contribution starts [55]. This contribution stops to rise the asymmetry value when the scalar product p μ .…”

“…This leads to the presence of the quark masses m u and m b in the denominator of the scalar term in (8). In turn, this will enable us to put more stringent bounds on the scalar operators contributions to this process [55].…”

“…The defined final-state polarizations, being quotients, are independent of the total number of B decay events considered. In our previous paper [55], we studied the bounds that can be set on the different couplings α J in the effective dimension-6 Lagrangian (1) involved in N mediated B decays by exploiting the experimental results existing on the B − → μ − μ − π + [56] and B − → μ − νγ [57] processes. Figure 6 in [55] shows different U 2 (m N ) (7) curves for the upper bounds obtained for the U 2 combination varying with the m N mass.…”

“…In this work we go on studying the effect on the B meson decays of the presence of a Majorana N with effective interactions. In a previous paper [55] we studied the constraints imposed by the bound on the B − → μ ± μ ∓ π + decay by LHCb [56] and in the radiative leptonic B → μνγ decay by Belle [57] on the effective operators. Here we propose to use final tau polarization and angular observables to disentangle the possible contributions of a Majorana neutrino N with effective interactions to the B − → τ − ν, the radiative B → μνγ and the LNV B…”