We present the key features relevant to the automated computation of all the leading-and next-to-leading order contributions to short-distance cross sections in a mixed-coupling expansion, with special emphasis on the first subleading NLO term in the QCD+EW scenario, commonly referred to as NLO EW corrections. We discuss, in particular, the FKS subtraction in the context of a mixed-coupling expansion; the extension of the FKS subtraction to processes that include final-state tagged particles, defined by means of fragmentation functions; and some properties of the complex mass scheme. We combine the present paper with the release of a new version of MadGraph5 aMC@NLO, capable of dealing with mixed-coupling expansions. We use the code to obtain illustrative inclusive and differential results for the 13-TeV LHC.

No abstract

Abstract:We compute the contribution of order α 2 S α 2 to the cross section of a topantitop pair in association with at least one heavy Standard Model boson -Z, W ± , and Higgs -by including all effects of QCD, QED, and weak origin and by working in the automated MadGraph5 aMC@NLO framework. This next-to-leading order contribution is then combined with that of order α 3 S α, and with the two dominant lowest-order ones, α 2 S α and α S α 2 , to obtain phenomenological results relevant to a 8, 13, and 100 TeV pp collider.

The electroweak contributions to the forward-backward asymmetry in the production of top-quark pairs at the Tevatron are evaluated at Oð 2 Þ and Oð 2 s Þ. We perform a detailed analysis of all partonic channels that produce an asymmetry and combine them with the QCD contributions. They provide a nonnegligible addition to the QCD-induced asymmetry with the same overall sign, thus enlarging the standard model prediction and diminishing the observed deviation. For the observed mass-dependent forwardbackward asymmetry a 3 deviation still remains at an invariant-mass cut of M t" t > 450 GeV.

We propose a method to determine the trilinear Higgs self coupling that is alternative to the direct measurement of Higgs pair production total cross sections and differential distributions. The method relies on the effects that electroweak loops featuring an anomalous trilinear coupling would imprint on single Higgs production at the LHC. We first calculate these contributions to all the phenomenologically relevant Higgs production (ggF, VBF, W H, ZH, ttH) and decay (γγ, W W * /ZZ * → 4f , bb, τ τ ) modes at the LHC and then estimate the sensitivity to the trilinear coupling via a one-parameter fit to the single Higgs measurements at the LHC 8 TeV. We find that the bounds on the self coupling are already competitive with those from Higgs pair production and will be further improved in the current and next LHC runs.