Scalar contributions to b→c(u)τν transitions

Abstract

We perform a comprehensive analysis of scalar contributions in b → cτ ν transitions including the latest measurements of R(D ( * ) ), the q 2 differential distributions in B → D ( * ) τ ν, the τ polarization asymmetry for B → D * τ ν, and the bound derived from the total width of the Bc meson. We find that scalar contributions with the simultaneous presence of both left-and right-handed couplings to quarks can explain the available data, specifically R(D ( * ) ) together with the measured differential distributions. However, the constraints from the total Bc width present a slight tension with the current data on B → D * τ ν in this scenario, preferring smaller values for R(D * ). We discuss possibilities to disentangle scalar new physics from other new-physics scenarios like the presence of only a left-handed vector current, via additional observables in B → D ( * ) τ ν decays or additional decay modes like the baryonic Λ b → Λcτ ν and the inclusive B → Xcτ ν decays. We also analyze scalar contributions in b → uτ ν transitions, including the latest measurements of B → τ ν, providing predictions for Λ b → pτ ν and B → πτ ν decays. The potential complementarity between the b → u and b → c sectors is finally investigated once assumptions about the flavour structure of the underlying theory are made.

Perturbative corrections to B → D form factors in QCD

“…which coincides with the previous determinations [4,5,67,[74][75][76][77] in the Standard Model (SM) at the 1 σ level and needs to be compared with the HFAG average value R(D) HFAG = 0.403 ± 0.040 ± 0.024 [2]. We mention in passing that the relatively high theory uncertainty of R(D) in (5.21), approximately 8%, can be traced back to the uncancelled hadronic uncertainties for determining the partial branching fraction of B → Dµν µ in the phasespace region 0 ≤ q 2 ≤ m 2 τ .…”

“…Inspecting the obtained results in table 3 indeed implies an incredibly precise one-percent accuracy of ∆R(t 1 , t 2 ), albeit with the implementation of much less accurate predictions for the hadronic form factors shown in table 1. Our predictions for the binned distributions of ∆R(t 1 , t 2 ) are also compatible with the recent determinations reported in [74], employing the B → D ν form factors extracted from a joint fit of the experimental data and two 2 The previous measurements from ALEPH, CLEO, Belle and BaBar summarized by the Heavy Flavor…”

“…Theory predictions for the partial decay rates of B → Dτ ν τ and for the binned distributions of ∆R(t 1 , t 2 ) defined in (5.20). The semileptonic B → D form factors obtained by fitting the experimental data with the Boyd-Grinstein-Lebed parametrization [66] are employed for the recent calculations presented in [74].…”

Simultaneous explanation of R(D (∗)) and b→sμ + μ −: the last scalar leptoquarks standing

“…W gauge bosons [11,14,53,54] 3. Leptoquarks [9,10,12,13,15,16,19,20,42,[55][56][57][58][59][60] Models with charged Higgses lead to (too) large effects in the total B c lifetime [61] and, depending on the coupling structure, can also be disfavored by the q 2 distribution [62][63][64]. Interestingly, if the couplings of the charged Higgs are chosen in such a way that they are compatible with the measured q 2 distribution, these models are ruled out by direct searches [65].…”

On the importance of electroweak corrections for B anomalies

“…[16][17][18][19][20][21][22]. In the recent literature, many studies focused on the experimental signatures implied by the solution of these anomalies in specific scenarios, including kaon observables [23,24], kinematic distributions in B decays [25][26][27][28][29][30][31][32][33][34][35], the lifetime of the B − c meson [36], Υ and ψ leptonic decays [37], tau lepton searches [38,39] and dark matter [40,41].…”