The role of right-handed neutrinos in $$ b\to c\tau \overline{v} $$ anomalies

Abstract

Motivated by the persistent anomalies reported in the b → cτν data, we perform a general model-independent analysis of these transitions, in the presence of light right-handed neutrinos. We adopt an effective field theory approach and write a low-energy effective Hamiltonian, including all possible dimension-six operators. The corresponding Wilson coefficients are determined through a numerical fit to all available experimental data. In order to work with a manageable set of free parameters, we define eleven wellmotivated scenarios, characterized by the different types of new physics that could mediate these transitions, and analyse which options seem to be preferred by the current measurements. The data exhibit a clear preference for new-physics contributions, and good fits to the data are obtained in several cases. However, the current measurement of the longitudinal D * polarization in B → D * τν cannot be easily accommodated within its experimental 1σ range. A general analysis of the three-body B → Dτν and four-body B → D * (→ Dπ)τν angular distributions is also presented. The accessible angular observables are studied in order to assess their sensitivity to the different new physics scenarios. Experimental information on these distributions would help to disentangle the dynamical origin of the current anomalies.

Constraining flavour patterns of scalar leptoquarks in the effective field theory

“…Another interesting measurement of the longitudinal polarization fraction for D * in the B → D * τν mode has been recently performed by Belle [77] where F D * L | exp = 0.60 ± 0.08 ± 0.035 lies 1.7σ above the SM expectation which is around 0.45 [73,78]. The corresponding expression including the NP operators can be written as [52]…”

Angular analysis of modes with $b \to c \ell \bar \nu$ transition and New Physics

“…Interestingly, in the B-rest frame ε µν (±2)q µ = 0, which implies that only three states of polarization contribute to the B → D * 2 ν decay and thus the number of transversity amplitudes (a total of sixteen) coincides with the vector meson case. We refer to [2,3] for more details. As can be seen from Eqs.…”

“…We use heavy-quark effective theory with Boyd, Grinstein and Lebed (BGL) parametrization for the B → D ( * ) form factors, including corrections of order α s , Λ QCD /m b,c and partly Λ 2 QCD /m 2 c . The inputs for form factor are obtained from lattice QCD, light-cone sum rules and QCD sum rules, without making use of experimental data [8,3]. We focus mainly on the effective operators which arise in presence of light RHN.…”

“…In this article we briefly highlight the key differences in the angular analysis of the B → D * (→ Dπ) ν and B → D * 2 (→ Dπ) ν decays and discuss how observables can be used to understand the effect of different New Physics (NP) scenarios contributing to these channels. We refer the reader to [2,3] for detailed derivations and discussions.…”

Relations between b → cτν decay modes in scalar models

“…Moreover, when some observables like R(D ( * ) ) deviate from the SM, then the simultaneous validity of the above relations is a hint for scalar models. In scalar models with right-handed neutrinos, see refs [145,159,205,206],. eqs.…”