Effective field theory approach to top-quark decay at next-to-leading order in QCD

We present analytical results for top-quark decay processes, in an effective field theory beyond the Standard Model, at next-to-leading order in QCD. We parametrize new physics effects using dimension-six operators, and consider all operators that give rise to non-standard interactions of the top quark. We investigate both the flavor-conserving and flavor-changing decay modes, including their two-body and three-body semi-leptonic final states. The QCD mixing among relevant operators are also taken into account. These results provide all information needed for a complete model-independent study of top-quark decay at next-to-leading order accuracy, paving the way to global analyses for new physics effects in an effective field theory approach.Comment: 34 pages, 7 figure

Top-quark decay into Higgs boson and a light quark at next-to-leading order in QCD

Neutral flavor-changing transitions are hugely suppressed in the Standard Model and therefore they are very sensitive to new physics. We consider the decay rate of t->u_i h where u_i=u,c using an effective field theory approach. We perform the calculation at NLO in QCD including the relevant dimension-six operators. We find that at NLO the contribution from the flavor-changing chromomagnetic operator is as important as the standard QCD correction to the flavor-changing Yukawa coupling. In addition to improving the accuracy of the theoretical predictions, the NLO calculation provides information on the operator mixing under the renormalization group.Comment: 8 pages, 5 figure