Constrained second-order power corrections in HQET: R(D⁽*⁾), |V_(cb)|, and new physics

Abstract

We postulate a supplemental power counting within the heavy quark effective theory (HQET) that results in a small, highly constrained set of second-order power corrections, compared to the standard approach. We determine all B̅ → D⁽*⁾ form factors, both within and beyond the standard model to O(αₛ/m_(c,b), 1/m²_(c,b)), under truncation by this power counting. We show that the second-order power corrections to the zero-recoil normalization of the B̅ → D⁽*⁾lν matrix elements (l = e, μ, τ) are fully determined by hadron mass parameters and are in good agreement with lattice QCD (LQCD) predictions. We develop a parametrization of these form factors under the postulated truncation, that achieves excellent fits to the available LQCD predictions and experimental data, and we provide precise updated predictions for the B̅ → D⁽*⁾τν̅ decay rates, lepton flavor universality violation ratios R(D⁽*⁾), and the Cabibbo-Kobayashi-Maskawa matrix element |V_(cb)|. We point out some apparent errors in prior literature concerning the O(1/m_(c)m_(b)) corrections and note a tension between commonly used simplified dispersive bounds and current data.