Abstract: We calculate the and form factors and decay rates for all possible four-Fermi interactions in and beyond the Standard Model (SM), including nonzero charged lepton masses and terms up to order in the heavy quark effective theory (HQET). We point out a subtlety involving the overcompleteness of the representation of the spin-parity antisymmetric tensor form factors, relevant also to other higher excited-state transitions, and present a general method for the counting of the physical form factors for any hadronic transition matrix element and their matching onto HQET. We perform a preliminary fit of a simple HQET-based parametrization of the form factors at to an existing quark model, providing preliminary predictions for the lepton universality ratios beyond the SM. Finally, we examine the possible incompatibility of recent lattice QCD results with expectations from the heavy-quark expansion and available experimental data.
Submitted to arXiv on 19 May. 2021
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