We calculate the complete differential decay distribution for the B meson
decay, BΛβD(β)βXΛ, to a massive right-handed (RH)
neutrino in the low-energy effective field theory (LEFT) framework. We find
that a massive RH neutrino does not introduce any new angular structures
compared to the massless case, but can cause significant distortions in angular
observables. We study the phenomenology of low-energy four-fermion operators
permitted by the standard model effective field theory (SMEFT) extended with RH
neutrinos (SMNEFT). We show that to explain the positive value of the
difference in forward-backward asymmetries, ΞAFBββ‘AFBΞΌββAFBeβ, tentatively inferred from Belle data, the
RH neutrino must be massive. We also make predictions for q2 dependent
angular observables to motivate future measurements.Comment: 12 pages, 4 figures, 3 table