D * polarization vs. R D(∗) anomalies in the leptoquark models

Polarization measurements in B → D(*)Ƭν̅ are useful to check consistency in new physics explanations for the RD and RD* anomalies. In this paper, we investigate the D* and Ƭ polarizations and focus on the new physics contributions to the fraction of a longitudinal D* polarization (F D*/L ), which is recently measured by the Belle collaboration F D*/L = 0:60 ± 0:09, in model-independent manner and in each single leptoquark model (R2, S1 and U1) that can naturally explain the RD(*) anomalies. It is found that B(B+/c → Ƭ⁺ν) severely restricts deviation from the Standard Model (SM) prediction of F D*/L,SM = 0:46 ± 0:04 in the leptoquark models: [0:43; 0:44], [0:42; 0:48], and [0:43; 0:47] are predicted as a range of F D*/L for the R2, S1, and U1 leptoquark models, respectively, where the current data of RD(*) is satised at 1 σ level. It is also shown that the Ƭ polarization observables can much deviate from the SM predictions. The Belle II experiment, therefore, can check such correlations between RD(*) and the polarization observables, and discriminate among the leptoquark models.