Precise Predictions for the Associated Production of a W Boson with a Top-Antitop Quark Pair at the LHC

The production of a top-antitop quark pair in association with a W boson (tt[over ¯]W) is one of the heaviest signatures currently probed at the Large Hadron Collider. Since the first observation reported in 2015, the corresponding rates have been found to be consistently higher than the standard model predictions, which are based on next-to-leading order calculations in the QCD and electroweak interactions. We present the first next-to-next-to-leading order QCD computation of tt[over ¯]W production at hadron colliders. The calculation is exact, except for the finite part of the two-loop virtual corrections, which is estimated using two different approaches that lead to consistent results within their uncertainties. We combine the newly computed next-to-next-to-leading order QCD corrections with the complete next-to-leading order QCD plus electroweak results, thus obtaining the most advanced perturbative prediction available to date for the tt[over ¯]W inclusive cross section. The tension with the latest ATLAS and CMS results remains at the 1σ-2σ level.

Higgs Boson Production in Association with a Top-Antitop Quark Pair in Next-to-Next-to-Leading Order QCD

The associated production of a Higgs boson with a top-antitop quark pair is a crucial process at the LHC since it allows for a direct measurement of the top-quark Yukawa coupling. We present the computation of the radiative corrections to this process at the next-to-next-to-leading order (NNLO) in QCD perturbation theory. This is the very first computation for a 2→3 process with massive colored particles at this perturbative order. We develop a soft Higgs boson approximation for loop amplitudes, which enables us to reliably quantify the impact of the yet unknown two-loop contribution. At the center-of-mass energy sqrt[s]=13  TeV, the NNLO corrections increase the next-to-leading order result for the total cross section by about 4% and lead to a significant reduction of perturbative uncertainties.

From Five-Loop Scattering Amplitudes to Open Trees with the Loop-Tree Duality

Characterizing multiloop topologies is an important step towards developing novel methods at high perturbative orders in quantum field theory. In this article, we exploit the Loop-Tree Duality (LTD) formalism to analyse multiloop topologies that appear for the first time at five loops. Explicitly, we open the loops into connected trees and group them according to their topological properties. Then, we identify a kernel generator, the so-called N7MLT universal topology, that allows us to describe any scattering amplitude of up to five loops. Furthermore, we provide factorization and recursion relations that enable us to write these multiloop topologies in terms of simpler subtopologies, including several subsets of Feynman diagrams with an arbitrary number of loops. Our approach takes advantage of many symmetries present in the graphical description of the original fundamental five-loop topologies. The results obtained in this article might shed light into a more efficient determination of higher-order corrections to the running couplings, which are crucial in the current and future precision physics program.

Transverse-momentum resummation for boson plus jet production at hadron colliders

We consider the associated production of a vector or Higgs boson with a jet in hadronic collisions. When the transverse momentum q T of the boson-jet system is much smaller than its invariant mass Q, the QCD perturbative expansion is affected by large logarithmic terms that must be resummed to all orders. We discuss the all-order resummation structure of the logarithmically enhanced contributions up to next-to-leading logarithmic accuracy. Resummation is performed at the differential level with respect to the kinematical variables of the boson-jet system. Soft-parton radiation produces azimuthal correlations that are fully accounted for in our framework. We present explicit analytical results for the resummation coefficients up to next-to-leading order and next-to-leading logarithmic accuracy, that include the exact dependence on the jet radius.

Mixed Strong-Electroweak Corrections to the Drell-Yan Process

We report on the first complete computation of the mixed QCD-electroweak (EW) corrections to the neutral-current Drell-Yan process. Superseding previously applied approximations, our calculation provides the first result at this order that is valid in the entire range of dilepton invariant masses. The two-loop virtual contribution is computed by using semianalytical techniques, overcoming the technical problems in the evaluation of the relevant master integrals. The cancellation of soft and collinear singularities is achieved by a formulation of the q_{T} subtraction formalism valid in the presence of charged massive particles in the final state. We present numerical results for the fiducial cross section and selected kinematical distributions. At large values of the lepton p_{T} the mixed QCD-EW corrections are negative and increase in size, to about -15% with respect to the next-to-leading-order QCD result at p_{T}=500  GeV. Up to dilepton invariant masses of 1 TeV the computed corrections amount to about -1.5% with respect to the next-to-leading-order QCD result.

Next-to-Next-to-Leading Order Event Generation for Top-Quark Pair Production

The production of top-quark pairs in hadronic collisions is among the most important reactions in modern particle physics phenomenology and constitutes an instrumental avenue to study the properties of the heaviest quark observed in nature. The analysis of this process at the Large Hadron Collider relies heavily on Monte Carlo simulations of the final state events, whose accuracy is challenged by the outstanding precision of experimental measurements. In this Letter we present the first matched computation of top-quark pair production at next-to-next-to-leading order in QCD with all-order radiative corrections as implemented via parton-shower simulations. Besides its intrinsic relevance for LHC phenomenology, this work also establishes an important step towards the simulation of other hadronic processes with color charges in the final state.

t t ¯ H production at NNLO: the flavour off-diagonal channels

We consider QCD radiative corrections to the associated production of a heavy-quark pair ( Q Q ¯ ) with a generic colourless system F at hadron colliders. We discuss the resummation formalism for the production of the Q Q ¯ F system at small values of its total transverse momentum q T . We present the results of the corresponding resummation coefficients at next-to-leading and, partly, next-to-next-to-leading order. The perturbative expansion of the resummation formula leads to the explicit ingredients that can be used to apply the q T subtraction formalism to fixed-order calculations for this class of processes. We use the q T subtraction formalism to perform a fully differential perturbative computation for the production of a top-antitop quark pair and a Higgs boson. At next-to-leading order we compare our results with those obtained with established subtraction methods and we find complete agreement. We present, for the first time, the results for the flavour off-diagonal partonic channels at the next-to-next-to-leading order.

Charge Asymmetry in Top Quark Pair Production

The top quark is the heaviest elementary particle known. It has been proposed many times that new physics beyond the current theory of elementary particles may reveal itself in top quark interactions. The charge asymmetry in the pair production of a fermion and its antiparticle has been known for many decades. Early measurements of such asymmetry in top quark pair production showed a disagreement with the prediction by more than 3 standard deviations. Many years of an effort on both experimental and theoretical side have allowed to understand the top quark pair charge asymmetry better and to bring back the agreement between the measurements and the theory. In this article, these efforts are reviewed together with the discussion about a potential future of such measurements.

The q T subtraction method: electroweak corrections and power suppressed contributions

Building upon the formulation of transverse-momentum resummation for heavy-quark hadroproduction, we present the first application of the q T subtraction formalism to the computation of electroweak corrections to massive lepton pairs through the Drell-Yan mechanism. We then study the power suppressed contributions to the q T subtraction formula in the parameter r cut , defined as the minimum transverse momentum of the lepton pair normalised to its invariant mass. We analytically compute the leading power correction from initial and final-state radiation to the inclusive cross section. In the case of initial-state radiation the power correction is quadratic in r cut and our analytic result is consistent with results previously obtained in the literature. Final-state radiation produces linear contributions in r cut that may challenge the efficiency of the q T subtraction procedure. We explicitly compute the linear power correction in the case of the inclusive cross section and we discuss the extension of our calculation to differential distributions.

Quark Transverse Parton Distribution at the Next-to-Next-to-Next-to-Leading Order

We report a calculation of the perturbative matching coefficients for the transverse-momentum-dependent parton distribution functions for quark at the next-to-next-to-next-to-leading order in QCD, which involves calculation of nonstandard Feynman integrals with rapidity divergence. We introduce a set of generalized integration-by-parts equations, which allows an algorithmic evaluation of such integrals using the machinery of modern Feynman integral calculation.