Probing lepton-flavour universality with decays

We analyse the rare processes in view of the recent hints of violations of lepton-flavour universality (LFU) observed in B meson decays. If, as suggested by present data, the new interactions responsible for LFU violations couple mainly to the third generation of left-handed fermions, decays turn out to be particularly interesting: these are the only kaon decays with third-generation leptons (the neutrinos) in the final state. In order to relate B -physics anomalies and K decays we adopt an effective field theory approach, assuming that the new interactions satisfy an approximate flavour symmetry. In this framework we show that O (1) deviations from the Standard Model predictions in branching ratios, closely correlated to similar effects in , are naturally expected. The correlation of , , and the LFU violations in B decays would provide a very valuable tool to shed more light on this interesting phenomenon.