Search

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 → uih where ui = u,c using an effective field theory approach. We perform the calculation at next-to-leading order (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. [ABSTRACT FROM AUTHOR]

We discuss new physics in top-quark interactions, using an effective-field-theory approach. We consider top-quark decay, single top production, and top-quark pair production. We identify 15 dimension-six operators that contribute to these processes, and we compute the deviation from the standard model induced by these operators. The results provide a systematic way of searching for (or obtaining bounds on) physics beyond the standard model. [ABSTRACT FROM AUTHOR]

We derive bounds from oblique parameters on the dimension-6 operators of an effective field theory of electroweak gauge bosons and the Higgs doublet. The loop-induced contributions to the ∆S, ∆T, and ∆U oblique parameters are sensitive to these contributions, and we pay particular attention to the role of renormalization when computing loop corrections in the effective theory. Limits on the coefficients of the effective theory from loop contributions to oblique parameters yield complementary information to direct Higgs production measurements. [ABSTRACT FROM AUTHOR]

The phenomenology of an unstable particle, including searches and exclusion limits at the LHC, depends significantly on its lineshape. When the width of the resonance is large with respect to its mass, off-shell effects become relevant and the very same definition of width becomes nontrivial. Taking a heavy Higgs boson as an example, we propose a new formulation to describe the lineshape via an effective field theory approach. Our method leads to amplitudes that are gauge invariant, respect unitarity, and can appropriately describe the lineshape of broad resonances. The application of the method to the following relevant processes for the LHC phenomenology have been considered: gluon fusion, vector boson scattering, and tt production via weak boson fusion. [ABSTRACT FROM AUTHOR]

Computations at next-to-leading order in the Standard Model offer new technical challenges in the presence of higher dimensional operators. We introduce a framework that, starting from the top-quark effective field theory at dimension six, allows one to make predictions for cross sections as well as distributions in a fully automatic way. As an application, we present the first complete results at next-toleading order in QCD for flavor-changing neutral interactions including parton shower effects, for tZ, th, tγ associated production at the LHC. [ABSTRACT FROM AUTHOR]