Constraining anomalous Wtb and related SMEFT couplings using low-energy and electroweak precision observables

A bstract We investigate constraints on couplings of Standard Model effective field theory (SMEFT) operators contributing to Wtb effective vertex at tree level. We study the one-loop level impact of these couplings on the low-energy flavour changing charged and neutral current processes and on the electroweak precision observables. We use the available data on these relevant processes to constrain the associated SMEFT/ Wtb couplings. Solving the renormalisation group equations, we connect the SMEFT couplings at different scales and use the bounds at low energy to obtain the relevant bounds at the large scale Λ. Our findings indicate significantly improved constraints on the couplings compared to existing constraints on Wtb couplings by ATLAS and CMS. Additionally, we predict branching ratios for various top-quark flavour-changing neutral current processes, which exceed SM expectations by several orders of magnitude but remain within the reach of future colliders. These SMEFT couplings, or anomalous couplings of the effective Wtb vertex, can further constrain different UV-complete and simplified models that generate such interactions at the tree or loop level.