Flavour symmetries in the SMEFT

A bstract We analyse how U(3) 5 and U(2) 5 flavour symmetries act on the Standard Model Effective Field Theory, providing an organising principle to classify the large number of dimension-six operators involving fermion fields. A detailed counting of such operators, at different order in the breaking terms of both these symmetries, is presented. A brief discussion about possible deviations from these two reference cases, and a simple example of the usefulness of this classification scheme for high- p T analyses at the LHC, are also presented.