Flavor anomalies, and the Bc lifetime

Discrepancies between theoretical expectations and experimental measurements of some heavy meson decays  have built up over the last decade. In particular, deviations are seen in decays of the pseudoscalar  B-meson to a K or a K* mesons accompanied by a mu+mu- pair, and as  increased rates of semileptonic decays of B-mesons into tau-leptons. We will first review the status of these so-called "flavor anomalies", including statistical analysis of new data published last month (Oct 2021). An important theoretical activity consists of constraining putative new-physics explanations of these anomalies through independent measurements. The lifetime  of the Bc meson is very well measured, and can be sensitive to the presence of new interactions that increase the rate of B decays to tau-leptons. We will present our recent effort to improve the theoretical estimate of the Bc lifetime and  describe some challenges encountered -- most notably,  the surprisingly limited success in the analogous calculation of lifetimes of B and D mesons. We take a stab at the possible underlying theoretical issues (aka, unjustifiable assumptions).