We investigate 2 → 3 QCD scattering amplitudes in multi-Regge kinematics, i.e. where the final partons are strongly ordered in rapidity. In this regime amplitudes exhibit intriguing factorisation properties which can be understood in terms of effective degrees of freedom called . Working within the Balitsky/JIMWLK framework, we predict these amplitudes for the first time to next-to-next-to-leading logarithmic order, and compare against the limit of QCD scattering amplitudes in full colour and kinematics. We find that the latter can be described in terms of universal objects, and that the apparent non-universality arising at NNLL comes from well-defined and under-control contributions that we can predict. Thanks to this observation, we extract for the first time the universal vertex that controls the emission of the central-rapidity gluon, both in QCD and $$ \mathcal{N} $$ = 4 super Yang-Mills.

Germany

Federico Buccioni

United Kingdom

Fabrizio Caola

United States

Federica Devoto

Giulio Gambuti

Investigating the universality of five-point QCD scattering amplitudes at high energy

We present a calculation of the bosonic contribution to the two-loop mixed QCD-electroweak scattering amplitudes for Z-boson production in association with one hard jet at hadron colliders. We employ a method to calculate amplitudes in the ’t Hooft-Veltman scheme that reduces the amount of spurious non-physical information needed at intermediate stages of the computation, to keep the complexity of the calculation under control. We compute all the relevant Feynman integrals numerically using the Auxiliary Mass Flow method. We evaluate the two-loop scattering amplitudes on a two-dimensional grid in the rapidity and transverse momentum of the Z boson, which has been designed to yield a reliable numerical sampling of the boosted-Z region. This result provides an important building block for improving the theoretical modelling of a key background for monojet searches at the LHC.

Switzerland

Piotr Bargieła

Herschel Chawdhry

Xiao Liu

Two-loop mixed QCD-electroweak amplitudes for Z+jet production at the LHC: bosonic corrections

We propose extensions of the anti-<math><msub><mi>k</mi><mi>t</mi></msub></math> and Cambridge/Aachen hierarchical jet clustering algorithms that are designed to retain the exact jet kinematics of these algorithms, while providing an infrared-and-collinear-safe definition of jet flavor at any fixed order in perturbation theory. Central to our approach is a new technique called interleaved flavor neutralization (IFN), whereby the treatment of flavor is integrated with, but distinct from, the kinematic clustering. IFN allows flavor information to be meaningfully accessed at each stage of the clustering sequence, which enables a consistent assignment of flavor both to individual jets and to their substructure. We validate the IFN approach using a dedicated framework for fixed-order tests of infrared and collinear safety, which also reveals unanticipated issues in earlier approaches to flavored jet clustering. We briefly explore the phenomenological impact of IFN with anti-<math><msub><mi>k</mi><mi>t</mi></msub></math> jets for benchmark tasks at the Large Hadron Collider.

Radosław Grabarczyk

Maxwell L. Hutt

Gavin P. Salam

Ludovic Scyboz

Jesse Thaler

Flavored jets with exact anti-<math><msub><mi>k</mi><mi>t</mi></msub></math> kinematics and tests of infrared and collinear safety

The production of Higgs bosons in weak boson fusion has the second largest cross section among Higgs-production processes at the Large Hadron Collider. As such, this process plays an important role in detailed studies of Higgs interactions with vector bosons. In this paper we extend the available description of Higgs boson production in weak boson fusion by considering anomalous weak interactions of the Higgs boson and next-to-next-to-leading order (NNLO) QCD radiative corrections at the same time. We find that, while leading order QCD predictions are too uncertain to allow for detailed studies of the anomalous couplings, next-to-leading order (NLO) QCD results are sufficiently precise, most of the time. The NNLO QCD corrections alter the NLO QCD predictions only marginally, but their availability enhances the credibility of conclusions based on NLO QCD computations.

Konstantin Asteriadis

Kirill Melnikov

Italy

Raoul Röntsch

Anomalous Higgs boson couplings in weak boson fusion production at NNLO in QCD

In this paper we consider signal-background interference effects in Higgs-mediated diphoton production at the LHC. After reviewing earlier works that show how to use these effects to constrain the Higgs boson total decay width, we provide predictions beyond NLO accuracy for the interference and related observables, and study the impact of QCD radiative corrections on the Higgs width determination. In particular, we use the so-called soft-virtual approximation to estimate interference effects at NNLO in QCD. The inclusion of these effects reduces the NNLO prediction for the total Higgs cross-section in the diphoton channel by about 1.7%. We study in detail the impact of QCD corrections on the Higgs-boson line-shape and its implications for the Higgs boson width extraction. In particular, we find that the shift of the Higgs resonance peak arising from interference effects gets reduced by about 30% with respect to the NLO prediction. Assuming an experimental resolution of about 150  $$\textrm{MeV}$$  <math> <mtext>MeV</mtext> </math>   on interference-induced modifications of the Higgs-boson line-shape, our NNLO analysis shows that one could constrain the Higgs-boson total width to about 10–20 times its Standard Model value.

Andreas Manteuffel

Lorenzo Tancredi

Signal-background interference effects in Higgs-mediated diphoton production beyond NLO

We compute the three-loop helicity amplitudes for   <math> <mi>q</mi> <mover> <mi>q</mi> <mo>¯</mo> </mover> </math>  $$ q\overline{q} $$  → gg and its crossed partonic channels, in massless QCD. Our analytical results provide a non-trivial check of the color quadrupole contribution to the infrared poles for external states in different color representations. At high energies, the qg → qg amplitude shows the predicted factorized form from Regge theory and confirms previous results for the gluon Regge trajectory extracted from qq′ → qq′ and gg → gg scattering.

Amlan Chakraborty

Three-loop helicity amplitudes for quark-gluon scattering in QCD

We use an abelian model to study linear power corrections which arise from infrared renormalons and affect event shapes in e + e  −  annihilation into hadrons. While previous studies explored power corrections in the two-jet region, in this paper we focus on the three-jet region, which is the most relevant one for the determination of the strong coupling constant. We show that for a broad class of shape variables, linear power corrections can be written in a factorised form, that involves an analytically-calculable function, that characterises changes in the shape variable when a soft parton is emitted, and a constant universal factor. This universal factor is proportional to the so-called Milan factor, introduced in earlier literature to describe linear power corrections in the two-jet region. We find that the power corrections in the two-jet and in the three-jet regions are different, a result which is bound to have important consequences for the determination of the strong coupling constant from event shapes. As a further illustration of the power of the approach developed in this paper, we provide explicit analytic expressions for the leading power corrections to the C-parameter and the thrust distributions in the N -jet region for arbitrary N, albeit in the abelian model.

Silvia Ravasio

Giovanni Limatola

Paolo Nason

Melih Ozcelik

Linear power corrections to e + e – shape variables in the three-jet region

We compute mixed QCD-electroweak corrections to the neutral-current Drell-Yan production of a pair of massless leptons in the high invariant mass region. Our computation is fully differential with respect to the final state particles. At relatively low values of the dilepton invariant mass, m  ℓℓ  ∼ 200 GeV, we find unexpectedly large mixed QCD-electroweak corrections at the level of −1%. At higher invariant masses, m  ℓℓ  ∼ 1 TeV, we observe that these corrections can be well approximated by the product of QCD and electroweak corrections. Hence, thanks to the well-known Sudakov enhancement of the latter, they increase at large invariant mass and reach e.g. −3% at m  ℓℓ  = 3 TeV. Finally, we note that the inclusion of mixed corrections reduces the theoretical uncertainty related to the choice of electroweak input parameters to below the percent level.

Matthias Heller

Chiara Signorile-Signorile

Mixed QCD-electroweak corrections to dilepton production at the LHC in the high invariant mass region

We compute the three-loop helicity amplitudes for the scattering of four gluons in QCD. We employ projectors in the ’t Hooft-Veltman scheme and construct the amplitudes from a minimal set of physical building blocks, which allows us to keep the computational complexity under control. We obtain relatively compact results that can be expressed in terms of harmonic polylogarithms. In addition, we consider the Regge limit of our amplitude and extract the gluon Regge trajectory in full three-loop QCD. This is the last missing ingredient required for studying single-Reggeon exchanges at next-to-next-to-leading logarithmic accuracy.

Andreas von Manteuffel

Three-Loop Gluon Scattering in QCD and the Gluon Regge Trajectory

We present a calculation of the helicity amplitudes for the process gg → γγ in three-loop massless QCD. We employ a recently proposed method to calculate scattering amplitudes in the ’t Hooft-Veltman scheme that reduces the amount of spurious non-physical information needed at intermediate stages of the computation. Our analytic results for the three-loop helicity amplitudes are remarkably compact, and can be efficiently evaluated numerically. This calculation provides the last missing building block for the computation of NNLO QCD corrections to diphoton production in gluon fusion.

Three-loop helicity amplitudes for diphoton production in gluon fusion