Origin of the remaining tension in semileptonic B-meson decays

Determine whether the remaining discrepancies between Standard Model predictions and experimental measurements of the lepton-flavor-universality observables in semileptonic B\(\to D^{(*)}\ell\nu_{\ell}\) decays arise from theoretical systematic uncertainties or from physics beyond the Standard Model.

Background

The paper performs a combined extraction of $|V_{cb}|$ using BGL form-factor fits constrained by lattice-QCD calculations, correlated large-recoil SCET sum rules, and Belle/Belle II decay data. It predicts $R(D)$ and $R(D^*)$, finding that the correlated Standard Model confidence region has little overlap with the experimental average.

The authors identify two broad possible explanations for this unresolved discrepancy: underestimated uncertainties in lattice-QCD and sum-rule form factors, or genuine contributions from physics beyond the Standard Model. Resolving the issue requires improved theoretical calculations and more precise Belle II measurements.