Implications of lepton flavor universality violations in B decays.

Present measurements of b→cτν and b→uτν transitions differ from the standard model predictions of lepton flavor universality by almost 4σ. We examine new physics interpretations of this anomaly. An effective field theory analysis shows that minimal flavor violating models are not preferred as an explanation, but are also not yet excluded.

Flavor changing neutral coupling mediated radiative top quark decays at next-to-leading order in QCD.

We compute the branching ratios for the rare top quark decays t→cγ and t→cZ mediated by effective flavor changing neutral couplings at next-to-leading order in QCD, including the effects due to operator mixing. After resumming contributions of the order of [α{s}log(Λ/m{t})]{n}, where Λ is the scale at which the effective operators are generated, using renormalization group methods, we compute finite matrix element corrections and study the effects of experimental kinematic cuts on the extracted branching ratios. We find that the t→cγ decay can also be used to probe the effective operators mediating t→cg processes, since the latter can naturally contribute 10% or more to the radiative decay.