Beta decay beyond the Standard Model in SMEFT

Standard Model Effective Field Theory (SMEFT) provides a model-independent framework for exploring physics beyond the Standard Model. The new physics effects are represented by operators with canonical dimensions D > 4 added to the SM Lagrangian. In this framework, corresponding Wilson coefficients are free parameters that must be determined from experimental data. In this work, we employ a one-loop renormalization-group (RG) improved perturbation theory to constrain relevant dimension-six Wilson coefficients from beta decay. Running the parameters from 5 TeV down to the electroweak scale, we investigate the operator mixing effects of the RG Equations, which introduce new parameters relevant to the beta decay at one loop. Due to the high precision of both experiments and the theory, we received results improving the bounds obtained from other processes at the tree level. In particular, we find a bound for the Wilson coefficient of the four-fermion operator involving light and top quarks to be 5×10^-3 which is an order of magnitude better than the result from the top pair production process.