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A bstract Subtraction schemes provide a systematic way to compute fully-differential cross sections beyond the leading order in the strong coupling constant. These methods make singular real-emission corrections integrable in phase space by the addition of suitable counterterms. Such counterterms may be defined using momentum mappings, which are parametrisations of the phase space that factorise the variables that describe the particles becoming unresolved in some infrared or collinear limit from the variables that describe an on-shell phase space for the resolved particles. In this work, we review existing momentum mappings in a unified framework and introduce new ones for final-collinear and soft counterterms. The new mappings work in the presence of massive particles and with an arbitrary number of soft particles or of clusters of collinear particles, making them fit for subtraction methods at any order in perturbation theory. The new mapping for final-collinear counterterms is also used to elucidate relations among existing final-collinear mappings.

Abstract We calculate the small-momentum expansion of vector, axial-vector, scalar, and pseudo-scalar heavy-quark current correlators in the large-β 0 limit of QCD, extending the analysis of Grozin and Sturm beyond the vector current. Our results are used to study the higher-order behaviour of dimensionless ratios of vector and pseudo-scalar moments used for the precise extraction of the strong coupling, α s , from relativistic quarkonium sum rules and lattice data, respectively. We show that these ratios benefit from a partial cancellation of the leading renormalon singularities. Our results can guide the design of combinations of moments with improved perturbative behaviour.

Abstract Building on earlier work on electroweak corrections to W-pair production, the first calculation of the full electroweak one-loop corrections to on-shell ZZ, W^sup ±^Z and γγ production at hadron colliders is presented, explicitly taking into account the full vector-boson mass dependence. As a consequence, our results are valid in the whole energy range probed by LHC experiments. Until now, the electroweak corrections have only been known in dedicated high-energy approximations limited to a specific kinematic regime, in particular requiring high boson transverse momenta. Therefore, our results comprise an important and so far missing ingredient to improve on the theory predictions for these fundamental Standard-Model benchmark processes also at intermediate energies and small scattering angles, where actually the bulk of events is located. In case of Z-pair production we have also included the leptonic decays and the associated weak corrections in our analysis. For this particular channel, corrections of about -4% are observed even close to the production threshold. For hard scattering processes with momentum transfers of several hundred GeV one finds large negative corrections which may amount to several tens of percent and lead to significant distortions of transverse-momentum and rapidity distributions.

Abstract In this work we compute for the first time the so-called Complete-NLO predictions for top-quark pair hadroproduction in association with at least one isolated photon (t t ¯ t̅ γ). We also compute NLO QCD+EW predictions for the similar case with at least two isolated photons (t t ¯ t̅ γγ) and for single-top hadroproduction in association with at least one isolated photon. In addition, we complement our results with NLO QCD+EW predictions of the hadronic and leptonic decays of top-quark including an isolated photon. All these results have been obtained in a completely automated approach, by extending the capabilities of the MadGraph5ₐMC@NLO framework and enabling the Complete-NLO predictions for processes with isolated photons in the final state. We discuss the technical details of the implementation, which involves a mixed EW renormalisation scheme for such processes.

Abstract We consider two-loop QCD corrections to the element Γ 12 q Γ₁₂^(q) of the decay matrix in B q − B ¯ q B̅_(q) mixing, q = d, s, in the leading power of the Heavy Quark Expansion. The calculated contributions involve one current-current and one penguin operator and constitute the next step towards a theory prediction for the width difference ∆Γ s matching the precise experimental data. We present compact analytic results for all matching coefficients in an expansion in m c /m b up to second order. Our new corrections are comparable in size to the current experimental error and slightly increase ∆Γ s .

We introduce an improvement to the FxFx matrix element merging procedure for pp →tt¯ W production at NLO in QCD with one and/or two additional jets. The main modification is an improved treatment of jets that are not logarithmically enhanced in the low transverse-momentum regime. We provide predictions for the inclusive cross section and the tt¯ W differential distributions including parton-shower effects. Taking also the NLO EW corrections into account, this results in the most-accurate predictions for this process to date. We further proceed to include the on-shell LO decays of the tt¯ W including the tree-level spin correlations within the narrow-width approximation, focusing on the multi-lepton signatures studied at the LHC. We find a ∼30% increase over the NLO QCD prediction and large non-flat K-factors to differential distributions.

Abstract Using modern multiloop calculation methods, we derive the analytical expressions for the total cross sections of the processes e − γ → e − X X ¯ e⁻XX̅ with X = μ, γ or e at arbitrary energies. For the first two processes our results are expressed via classical polylogarithms. The cross section of e − γ → e − e − e + is represented as a one-fold integral of complete elliptic integral K and logarithms. Using our results, we calculate the threshold and high-energy asymptotics and compare them with available results.