The impact of flavour data on global fits of the MFV SMEFT

Abstract

We investigate the information that can be gained by including flavour data in fits of the Standard Model Effective Field Theory (SMEFT) with the assumption of Minimal Flavour Violation (MFV), allowing — as initial conditions at the high scale — leading terms in spurionic Yukawas only. Starting therefore from a theory with no tree level flavour changing neutral currents at the scale of new physics, we calculate effects in flavour changing processes at one loop, and the resulting constraints on linear combinations of SMEFT coefficients, consistently parameterising the electroweak parameters and the CKM within the SMEFT. By doing a global fit including electroweak, Higgs and low energy precision measurements among others, we show that flavour observables put strong constraints on previously unconstrained operator directions. The addition of flavour data produces four independent constraints at order TeV or above on otherwise flat directions; reducing to three when complete U(3)5 flavour symmetry is assumed. Our findings demonstrate that flavour remains a stringent test for models of new physics, even in the most flavourless scenario.