High Precision for Hard Processes (HP2 2026)

Oct 5, 2026, 1:45 PM → Oct 9, 2026, 3:30 PM Europe/Berlin

NTI Hörsaal, building 30.10 (KIT)

Bakar Chargeishvili (KIT), Gudrun Heinrich (KIT), Kirill Melnikov (TTP KIT), Matthias Kerner (KIT), Matthias Steinhauser (KIT), Stefano Di Noi (KIT (ITP))

The 10th International Workshop on High Precision for Hard Processes at the LHC (HP² 2026) will be held at Karlsruhe Institute of Technology (KIT) on October 5-9, 2026.

This series of workshops is devoted to high-precision studies of hard scattering processes at hadron colliders and beyond. The main themes are recent developments and new results for theoretical computations in quantum field theory and their applications to collider phenomenology. These topics are particularly relevant as the LHC experiments at CERN will be entering a new phase of precision measurements.   

Topics:

• Precise predictions for Standard Model phenomenology and beyond
• New mathematical techniques for amplitude calculations and their automation
• Status reports, implications of current LHC results and prospects for future colliders

 

Please beware of phishing Emails about accommodation! We do not provide any service to book accommodation, if you receive such Emails, please ignore them.

Note that the workshop VBF 2026: Precision in VBF Higgs production in the context of the High-Luminosity LHC, will take place in the week before HP2 in Aachen. Karlsruhe can be easily reached by train from Aachen.

Confirmed plenary speakers:

• Thomas Becher
• Anke Biekötter
• Simone Devoto
• Monica Dunford
• Thomas Gehrmann
• Stephen Jones
• Alexander Karlberg
• Markus Klute
• Yan-Qing Ma
• Daniel Maitre
• Sven-Olaf Moch 
• Mathieu Pellen
• Stefano Pozzorini
• Daniel Reichelt
• Juan Rojo
• Heidi Rzehak
• Chiara Signorile-Signorile
• Vasily Sotnikov
• Michael Spannowsky
• Simone Zoia

 

Abstract submission deadline: July 15, 2026

Early Bird Fee until July 31, 2026

Registration deadline: August 31, 2026

 

International Advisory Committee:

Charalampos Anastasiou (Zurich, ETH), Stefan Dittmaier (Freiburg University), Daniel de Florian (Buenos Aires, ICAS-UNSAM), Thomas Gehrmann (Zurich University), Massimiliano Grazzini (Zurich University), Gudrun Heinrich (Karlsruhe, KIT), Stephen P. Jones (Durham, IPPP), Zoltan Kunszt (ETH Zurich), Lorenzo Magnea (University of Torino)

 

Local Organising Committee:

Bakar Chargeishvili,  Stefano Di Noi, Gudrun Heinrich, Matthias Kerner, Kirill Melnikov, Matthias Steinhauser

Previous HP2 workshops:

 

2006: Zürich

2008: Buenos Aires

2010: Florence

2012: Munich

2014: Florence

2016: Buenos Aires

2018: Freiburg

2022: Durham/Newcastle

2024: Torino

Poster HP2 2026 - A3.pdf

Poster HP2 2026.pdf

Poster HP2 2026.png

Mon, October 5

1:45 PM → 3:45 PM Plenary

Convener: Gudrun Heinrich (KIT)

1:45 PM Welcome and information

Speaker: Gudrun Heinrich (KIT)

Welcome_HP2_2026.pdf

2:00 PM Recent LHC measurements and prospects for HL-LHC

Speaker: Monica Dunford

2026_10_HP2.pdf

2:45 PM Precision Higgs Physics

Speaker: Alexander Karlberg (Max Planck Institute for Physics)

Higgs_precision_karlberg.pdf

3:15 PM Top quark physics

Speaker: Sven-Olaf Moch (Universität Hamburg)

hp2-2026-top.pdf

3:45 PM → 4:15 PM Coffee break

4:15 PM → 5:55 PM Track 1 - IBP: Parallel Session I

Convener: Vitaly Magerya

4:15 PM Untangling the IBP equations

In this talk, we will present a general strategy for solving integration-by-parts (IBP) identities. Our approach is based on the diagonalisation of the IBP system, which effectively reduces it to single-variable recurrence relations. To the best of our knowledge, this is achieved here for the first time of its use. This framework yields an iterative reduction procedure that enables highly efficient solutions for high-rank integrals and provides a direct route to closed-form solutions. The diagonalisation algorithm further gives rise to a novel class of reduction rules, which we term the triangular approach. This method is tailored to QCD multi-loop reductions, where it leads to significant improvements in computational efficiency.

Speaker: Junhan William Liu (University of Cambridge)

IBP_talk_HP2.pdf

4:40 PM Progress towards numerical reduction at two-loops within the HELAC framework

I will present the current status in constructing a generic two-loop amplitude reduction algorithm within the HELAC computational framework. Following HELAC tree- and one-loop paradigm, we have completed the generation and validation of the two-loop amplitude-integrand as well as the algebraic reduction for Leading Color gg -> gg. I will present numerical construction and reduction results of the amplitude in d = 4 − 2ε dimensions. Following the OPP reduction approach, we express the amplitude in terms of Feynman integrals which are further reduced to master integrals through the IBP identities.

Speaker: Dr Aris Spourdalakis (NCSR Demokritos)

HP2_2026_Talk_final_spourdalakis.pdf

5:05 PM Efficient Reconstruction of Scattering Amplitudes

We present a new method for reconstructing scattering amplitudes directly in partial-fractioned form. By evaluating the amplitude on its singular surfaces, we derive constraints on the coefficients in the partial-fractioned ansatz. These constraints significantly reduce the number of integration-by-parts samples required for the reconstruction. The resulting amplitude representation is substantially smaller than the corresponding representation in the common-denominator form. We demonstrate the effectiveness of our method by applying it to state-of-the-art amplitude calculations.

Speaker: Anton Olsson (Karlsruhe Institute of Technology)

hp2_2026.pdf

5:30 PM Infrared divergences and Feynman integral reduction

One of the bottlenecks in multiloop amplitude calculations is integration-by-parts (IBP) reduction of the underlying Feynman integrals. In this talk, I will present a recent approach that organizes IBP reduction according to the infrared singularity structure encoded in the Landau equations. More precisely, I will show how syzygy solutions describing unitarity-compatible IBP relations are linked to Landau singularities, and how this connection allows us to construct universal, compact syzygies. I will illustrate the method with explicit examples at one and two loops.

Speaker: Pavel Novichkov (Ghent University)

Pavel_HP2.pdf

4:15 PM → 5:55 PM Track 2 - EW HH: Parallel Session I

Convener: Matthias Steinhauser (KIT)

4:15 PM NLO EW corrections to 𝑔𝑔 → 𝐻𝐻 in the forward limit

We present an analytical approach for the calculation of the top quark contribution to the two-loop electroweak 𝑔𝑔 → 𝐻𝐻 amplitude. The amplitude is considered in the forward limit, where the Mandelstam variable 𝑡 is small. We expand the amplitude at the level of the integrands and obtain good approximations for large parts of the phase space.

Speaker: Dominik Grau (Karlsruher Institute of Technology)

Grau_HP2_HH.pdf

4:40 PM Electroweak effects in Higgs boson pair production: The quark case

We present a study of quark-initiated contributions to Higgs boson pair production. Our result include the NLO QCD corrections to the electroweak quark-antiquark channel and the interference between the electroweak and QCD quark-initiated amplitudes. We compute the two-loop amplitudes analytically using the method of differential equations, with boundary conditions obtained from the large-mass expansion of the canonical master integrals. The one-loop amplitudes are computed using GoSam. All results are implemented in the POWHEG-BOX framework for phenomenological studies, resulting in sizable distortions of differential distributions.

Speaker: Philipp Rendler (Institute for Theoretical Physics, Karlsruhe Institute of Technology)

HP2_2026_Philipp_Rendler.pdf

5:05 PM Higgs-Pair Production via Gluon Fusion: Top-Yukawa- and light-quark-induced electroweak Corrections

After the discovery of the Higgs boson in 2012, the measurements of the Higgs self coupling is still a challenge for current and future experiments in particle physics.
Higgs-boson pair production via gluon fusion is a loop-induced process. In order to increase the accuracy of the theoretical predictions for this process, higher-order corrections are necessary to reduce theoretical uncertainties and to describe differential distributions reliably. The next-to-leading order (NLO) corrections involve the evaluation of two-loop Feynman diagrams. In particular, for electroweak (EW) corrections, many different mass scales appear in the calculation, such as the gauge boson, bottom, top quark, and Higgs boson masses. Further complications include numerical instabilities due to virtual thresholds which require careful treatment. In my talk, I will present results for the EW corrections induced by the top-Yukawa coupling with contributions from light-quark loops without using any reduction techniques to master integrals. The calculations are done by keeping the masses as fully symbolic parameters, allowing, in the future, for a study of parametric and mass scheme/scale uncertainties. I will furthermore discuss the next steps towards the calculation of the full EW corrections in our framework.

Speaker: Sauro Carlotti (Karlsruher Institut für Technologie - ITP)

Sauro_HP2.pdf

5:30 PM On the road to full electroweak corrections to Higgs boson pair production in gluon fusion

One of the main goals for the HL-LHC is the measurement of the
trilinear Higgs self-coupling, which can be accessed directly in
processes producing two Higgs bosons simultaneously. Higher order
perturbative corrections to gluon fusion, the dominant production
channel, have a sizable impact on the extracted constraints. In
particular, NLO electroweak corrections distort the differential
crosssections.
The amplitude contains chiral couplings and two-loop integrals with up
to five scales. This talk presents an overview over the calculation of
the full EW corrections at NLO, as well as some preliminary
phenomenological results.

Speaker: Augustin Vestner (KIT-ITP)

HP2_2026_AVestner.pdf

4:15 PM → 5:55 PM Track 3 - Resummation / IR: Parallel Session I

Convener: Gabor Somogyi

4:15 PM Automated calculation of gluon jet functions

We present an automated framework for the computation of gluon jet functions to next-to-next-to-leading order (NNLO) in perturbation theory. Our formalism builds on the SoftSERVE strategy that is used to isolate the implicit phase-space divergences of the collinear matrix elements, keeping the observable-specific measurement function generic. This separation enables the numerical evaluation of the remaining integrals and provides a flexible tool for high-order calculations of jet observables. We demonstrate the method by obtaining new NNLO results for both unpolarised and polarised gluon jet functions for several event-shape variables.

Speaker: Kevin Marc Brune (JGU Mainz)

HP2_Brune.pdf

4:40 PM Gluon Jet Function for transverse-momentum-like variables in NNLO QCD

We present the computation of the gluon jet function for transverse-momentum-like resolution variables at next-to-next-to-leading order in perturbative QCD. We discuss the relevance of the computation in the context of slicing methods for multi-jet production processes, obtaining results for two jet recombination schemes, namely the E-scheme and the WTA-scheme. The emergence of rapidity divergences is addressed using a time-like auxiliary vector as a rapidity regulator.

Speaker: Giovanbattista Favorito (University of Zurich)

HP2_presentation_favorito.pdf

5:05 PM Collinear functions up to NNLO in QCD

The singular behaviour of QCD squared amplitudes in the collinear limit is factorized and controlled by splitting kernels with a process-independent structure. We use these kernels to define collinear functions that can be used in resummation formulae of hard-scattering observables. Different collinear functions are obtained by integrating the splitting kernels over different phase-space regions that depend on the hard-scattering observables of interest. To circumvent the rapidity divergences encountered in the case of transverse-momentum-like observables, we employ a time-like auxiliary vector in our calculation. We present the results of explicit computations of various collinear functions up to NNLO in QCD.

Speaker: Prasanna Dhani (University of Zurich)

Dhani@HP2-2026.pdf

5:30 PM Precise predictions for Higgsstrahlung at future colliders

We shall present the computation of differential observables including higher order QCD corrections up to NNLO level.

Speaker: Aude Gehrmann-De Ridder (ETH Zurich)

HP2_26_AudeGehrmann.pdf

6:30 PM → 8:00 PM Reception

Tue, October 6

9:00 AM → 10:30 AM Plenary

Convener: Massimiliano Grazzini (University of Zürich)

9:00 AM Recent developments in slicing and subtraction methods for higher-order QCD calculations at colliders

Speaker: Chiara Signorile-Signorile

9:30 AM Analyticity Bootstrap of Feynman Integrals

Speaker: Yan-Qing Ma (Peking U.)

10:00 AM Recent developments in parton showers

Speaker: Daniel Reichelt (CERN)

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:40 PM Track 1 - Analytic integrals: Parallel Session II

Convener: Sven Moch

11:00 AM Feynman Integrals from First Principles: Positivity, Analyticity, and Padé Approximants

Precise predictions for cross-sections at present and future particle colliders require reliable methods for evaluating multi-loop Feynman integrals, which are often beyond the reach of direct analytic techniques. In this talk, I will present new numerical approaches that exploit general structural properties of quantum field theory—such as positivity and analyticity—to compute Feynman integrals efficiently from limited input data. A key new insight is that, in the Euclidean region, scalar Feynman integrals obey complete monotonicity, a powerful and largely unexplored constraint that, when combined with their differential equations, allows their numerical values to be tightly constrained within a systematic bootstrap framework. Moreover, in a broad range of space-time dimensions and propagator powers, Feynman integrals fall into the class of Stieltjes functions, which guarantees the convergence of Padé approximations in the complex plane. This provides a natural framework for constructing accurate rational approximations that remain valid under analytic continuation to physical scattering regions. These ideas point toward a broadly applicable paradigm for numerical multi-loop calculations relevant to collider phenomenology, while highlighting deep connections between Feynman integrals and fundamental principles of quantum field theory.

Speaker: Johannes Henn (Max Planck Institute for Physics)

11:25 AM Bootstrapping Six-Gluon QCD Amplitudes

We present a bootstrap construction of planar two-loop six-gluon scattering amplitudes, focusing on the ``most complicated terms'' in the sense of Lipatov. From an analysis of on-shell diagrams, we identify a complete and conformally invariant set of leading singularities. Combining these results with recent advances in understanding the relevant function space and with insights from generalized unitarity, we find that the considered helicity amplitudes are uniquely determined by imposing correct physical limits. This yields the first detailed picture of two-loop six-gluon amplitudes at the symbol. It also reveals a remarkably small and tightly constrained function alphabet, hinting at a deeper organizing principle similar to that observed in maximally supersymmetric Yang–Mills theory. Our results provide a new perspective on multi-particle scattering in pure Yang–Mills theory and pave the way for systematic extensions to higher multiplicities.

Speaker: Qinglin Yang (Max Planck Institute for Physics, Garching, Germany)

Karlsruhe.pdf

11:50 AM From Leading Singularities to Canonical Bases

The relationship between unit leading singularities and canonical differential equations has played a central role in modern multi-loop calculations. While this connection is well understood for polylogarithmic integrals, its extension to more general classes of functions has remained unclear.

In this talk, I will present a generalized notion of leading singularities that naturally extends to elliptic and more complicated geometries. The construction explains why new transcendental functions necessarily appear in canonical bases beyond polylogarithms and shows how they can be identified through a generalized integrand analysis going beyond the $\epsilon=0$ limit. Once the leading singularities are properly normalized, the corresponding master integrals satisfy $\epsilon$-factorized differential equations in complete analogy with the polylogarithmic case.

This analysis provides a systematic framework for identifying canonical master integrals beyond polylogarithms, which are relevant to future high-precision calculations. I will illustrate the general concepts with explicit examples, starting with the simplest beyond-polylogarithmic example, namely, elliptic curves, and progressing to more general Calabi-Yau geometries.

Speaker: Christoph Nega (Max Planck Institut für Gravitationsphysik)

12:15 PM Feynman Integrals Meet Second-Order Partial Differential Equations

We propose a second-order partial differential equation method to solve multi-loop Feynman integrals as an equilibrium problem. As a proof-of-concept demonstration, we perform a Galerkin discretization of the corresponding variational form and employ the finite element method to compute two-loop four-point Feynman integrals. This method can solve the integral over a broad region of multi-dimensional phase space once and for all. This work establishes a new connection between perturbative quantum field theory and modern partial differential equation methods.

Speaker: Hantian Zhang (CERN)

PDE_Zhang_HP2_2026.pdf

11:00 AM → 12:40 PM Track 2 - Soft Functions / Resummation: Parallel Session II

Convener: Aude Gehrmann-DeRidder

11:00 AM $N$-jettiness Soft function with massive partons at NNLO

The soft function is a key ingredient in the implementation of $N$-jettiness slicing. At next-to-next-to-leading order (NNLO), $N$-jettiness soft functions are known for arbitrary $N$ in the case of massless particles. We present an extension of this calculation to processes involving massive partons, thereby enabling applications to processes with top quarks, such as $t \bar t$ + jet production. Our framework enables the fully analytic cancellation of infrared and collinear singularities between the bare soft function and its renormalization matrix. As a result, we obtain a ready-to-implement expression for the renormalized soft function.

Speaker: Prem Agarwal

11:25 AM Universal feature of NLP corrections

The inclusion of next-to-leading-power (NLP) corrections is essential for achieving the percent-level theoretical precision required at the LHC. We present a new approach, based on soft theorems, for calculating leading logarithms at NLP for a variety of jet-associated processes and demonstrate their universal features for both soft-gluon and soft-quark radiation.

Speaker: Sourav Pal (JGU Mainz)

11:50 AM Soft-photon resummation for low-energy e⁺e⁻ scattering

Precision studies of low-energy e⁺e⁻ annihilation, most notably the extraction of the hadronic vacuum polarisation contribution to the muon anomalous magnetic moment, require theoretical control over the multi-photon radiation phase-space. This demands inclusion of soft photon emission to all orders, consistently matched to fixed-order cross-sections.
I present a Fortran implementation of Coherent Exclusive Exponentiation (CEEX), based on the Yennie–Frautschi–Suura (YFS) formalism, for lepton and hadron pair production at low centre-of-mass energies. CEEX organises the emission of an arbitrary number of photons into a coherent sum over photon multiplicities, exponentiating the infrared-singular part of the amplitude while retaining exact spin correlations and hard photon contributions order by order in perturbation theory. The residual hard-photon amplitudes entering the exponentiated cross section are obtained via a tensor decomposition of the underlying Feynman amplitudes, providing a systematic route to incorporate higher-order (NNLO) corrections consistently into the resummed prediction.
I will describe the structure and numerical implementation of the CEEX algorithm, discuss validation against fixed-order and alternative exponentiation schemes, and present first results for muon and pion pair production. This work is developed within the RadioMonteCarlow2 initiative, aiming to deliver next-generation precision Monte Carlo tools for radiative-return and energy-scan experiments at low-energy e⁺e⁻ colliders.

Speaker: Jeremy Paltrinieri (University of Liverpool)

Slides_HP2_JP.pdf

12:15 PM Threshold resummation of rapidity distributions at fixed partonic rapidity

I present an all-order direct-QCD resummation of rapidity distributions in the threshold limit at fixed partonic rapidity. The formalism is applied to Drell–Yan production, where matching to NNLO determines the resummation coefficients up to NNLL accuracy. I then show the equivalence between our approach and the corresponding SCET formulation.

Speaker: Davide Maria Tagliabue (KIT (TTP))

HP2_Tagliabue.pdf

12:40 PM → 12:50 PM Conference Photo

12:50 PM → 2:00 PM Lunch

2:00 PM → 3:30 PM Plenary

Convener: Matthias Steinhauser (KIT)

2:00 PM Precision electroweak physics at the LHC and at future colliders

Speakers: Mathieu Pellen, Mathieu Pellen (University of Freiburg)

PELLEN_HP2_2026.pdf

2:30 PM Loop-Tree and Loop-Loop Duality with OpenLoops

Speaker: Stefano Pozzorini

3:00 PM Numerical methods for electroweak corrections and applications

Speakers: Simone Devoto, Simone Devoto (University of Ghent)

HP226.pdf

3:30 PM → 4:00 PM Coffee break

4:00 PM → 6:00 PM Track 1 - Numeric integration: Parallel Session III

Convener: Valentin Hirschi

4:00 PM Recursive reduction of two-loop tensor integrals for automated NNLO calculations

Next-to-next-to-leading order corrections are essential for meeting the precision goals of the LHC and future colliders, making efficient automated NNLO tools increasingly important. Within the OpenLoops framework, the calculation involves loop-momentum tensor integrals, process-dependent tensor coefficients, and process-independent UV and rational counterterms. We present a new recursive algorithm that reduces arbitrary two-loop tensor integrals to scalar integrals, which are then further reduced to master integrals and evaluated using standard tools. The algorithm has been implemented in an efficient numerical code that can be interfaced with OpenLoops, allowing all ingredients of the calculation to be combined in an automated way. We discuss the current status of the implementation, with emphasis on validation, performance, and numerical stability.

Speaker: Fabian Lange (Universität Zürich and PSI Center for Neutron and Muon Sciences)

HP2_Lange.pdf

4:25 PM Numerical Evaluation of Multivariate Hypergeometric Functions Using HyperPrecision

Multivariate hypergeometric functions appear in many areas of theoretical physics and mathematics. We present HyperPrecision, a Mathematica package for the high-precision numerical evaluation of multivariate hypergeometric functions and their $\varepsilon$-expansions. In this talk, we will discuss the algorithm and demonstrate the use of the package, with applications including Feynman integrals and cosmological correlators.

Speaker: Souvik Bera (Asia Pacific Center for Theoretical Physics)

4:50 PM Exponentially Converging Numerical Evaluation of Iterated Integrals

We present a method for the high-precision numerical evaluation of transcendental functions appearing in Feynman integrals, based on a natural extension of known techniques for approximating transcendental numbers by rationals. The method easily achieves 100+ digits of precision, is systematically improvable and applies broadly to periods of elliptic curves and Calabi-Yau manifolds, as well as to more general iterated integrals. We also discuss prospects for extending this approach to the direct numerical evaluation of complete Feynman integrals.

Speaker: Thomas Stone (Technical University of Munich (TUM))

5:15 PM Feynman integrals numerical evaluation with LINE

We present the latest developments in LINE, a publicly available computer program for the numerical evaluation of Feynman integrals. By solving differential equations through series expansions, LINE computes boundary values and propagates them efficiently across different kinematic regions while maintaining a strict control over numerical precision. Designed for large-scale computations to tackle the challenges set by present and future collider physics experiments, our code is written in C/C++ and is based entirely on open-source libraries.

Speaker: Renato Maria Prisco (Max Planck Institute for Physics)

4:00 PM → 6:00 PM Track 2 - IR: Parallel Session III

Convener: Chiara Signorile-Signorile

4:00 PM Local Analytic Sector Subtraction with initial-state hadrons: Infrared kernels and their integration

In this talk, I will present our recent work on the analytic integration of infrared kernels within the framework of Local Analytic Sector Subtraction. We derive integrated counterterms for initial-state soft and collinear radiation using exact phase-space factorisations. Together with previous work on final-state radiation, these results provide the analytic building blocks needed for generic NNLO QCD calculations at hadron-hadron and lepton-hadron colliders.

Speaker: Yashasvee Goel (University of Torino and INFN Torino)

HP2_Goel_2026.pdf

4:25 PM Recent developments in NNLOCAL

Recently, we presented an extension of the CoLoRFulNNLO local subtraction framework for computing higher-order radiative corrections to hadron-initiated processes. Specifically, initial-state radiation has been regularized by introducing analytically integrable counterterms that lead to a relatively small number of counter-events. We have also released a proof-of-concept code, NNLOCAL, which contains an implementation of our method. In this talk, we discuss our ongoing efforts to transform this code into a production-grade tool. We highlight in particular recent improvements designed to streamline usability, facilitate extensibility, and optimise numerical performance.

Speaker: Gabor Somogyi (HUN-REN Wigner Research Centre for Physics)

4:50 PM A perturbative framework to probe infrared sensitivity in non-Abelian gauge theories

Understanding the infrared sensitivity of perturbative predictions in QCD is important for assessing the magnitude of possible non-perturbative power corrections to processes with large momentum transfer. In renormalon models, this sensitivity can be related to computable dependences of perturbative quantities on a small gluon mass. However, this procedure cannot be applied to collider processes with gluons at the Born level.
To address this problem, we promote the gluon mass to a parameter of a consistent non-Abelian quantum field theory where the gauge symmetry is spontaneously broken through the Higgs mechanism. Working in the limit in which the gluon mass $m_g$ is the smallest dimensionful parameter, we compute through two loops the $\mathcal{O}(m_g)$ contributions to the relation between the pole and $\overline{\rm MS}$ masses of a heavy quark and to the relation between corresponding field counterterms. We also report on first steps towards applying this framework to computing $\mathcal{O}(m_g)$ contributions to top-pair production through two loops. We expect that the proposed framework will provide a useful laboratory for probing linear infrared sensitivity of this and other collider observables in QCD.

Speaker: Dennis Horstmann (KIT)

5:15 PM A general subtraction formula at NNLO in QCD with massless partons

Beyond leading order in QCD, infrared singularities arise in real and virtual corrections and must cancel in physical observables. At NNLO, organising this cancellation becomes considerably more involved due to the presence of a myriad of unresolved limits. I will discuss how these can be systematically treated within the nested soft-collinear subtraction scheme for arbitrary processes with massless partons. This leads to a fully local, analytic and process-independent subtraction framework, in which the NNLO cross section is written in terms of explicitly finite contributions, completing the generalization of the scheme to arbitrary massless QCD processes at NNLO.

Speaker: Matteo Tresoldi (KIT TTP)

Wed, October 7

9:00 AM → 10:00 AM Plenary

Convener: Stephen Jones (IPPP Durham)

9:00 AM Factorisation: violated or not?

Speaker: Thomas Becher (Universität Bern)

9:30 AM Analytic methods for multi-loop amplitudes

Speaker: Vasily Sotnikov (University of Zurich)

10:00 AM → 10:30 AM Coffee break

10:30 AM → 12:10 PM Track 1 - Many Loops / Legs: Parallel Session IV

Convener: Kay Schönwald

10:30 AM QCD decoupling @ five loops

We present new results for the decoupling of the strong coupling constant at five loop order

Speaker: Peter Marquard (DESY)

10:55 AM Higher Intersection Pairings for Hard Processes

Precision predictions for collider and gravitational-wave observables rely on the efficient evaluation and reduction of multi-loop Feynman integrals. I will present a method for constructing differential equations for Feynman integrals directly from multivariate intersection numbers, bypassing the solution of large systems of integration-by-parts identities. The method exploits the large-$\varepsilon$ expansion of intersection numbers, whose coefficients are known as higher residue pairings. These pairings are naturally defined for analytically regulated integrals; in the vanishing-regulator limit, they recover the relative cohomology framework, leading to a drastic simplification of the resulting formulae. The pairings localise at the critical points of the associated potential, organising the computation sector by sector, while the corresponding sums over critical points can be evaluated purely algebraically using companion-matrix techniques. As an application, I will construct canonical differential equations for massless planar ladder integrals up to four loops.

Speaker: Giacomo Brunello (Scuola Normale Superiore)

11:20 AM Three-loop amplitudes for quark-initiated diboson production in the leading-color approximation

I will present the computation of the three-loop QCD scattering amplitudes for the production of two massive vector bosons in the quark annihilation channel, in the generalized leading-color approximation. These amplitudes constitute a key ingredient for the virtual contribution to the N3LO QCD corrections for electroweak gauge-boson pair production at hadron colliders and represent an important step towards precise predictions in view of the high-luminosity phase of the LHC. The amplitudes are expressed in terms of a basis of special functions multiplied by kinematic rational coefficients, which are reconstructed analytically using finite-field techniques, making use of projectors method and compact IBP systems. The special functions are then evaluated by solving systems of differential equations.

Speaker: Dhimiter Canko (University of Turin)

11:45 AM Three-loop mixed QCD-EW form factors to the on-shell $Z$ production at hadron colliders

The Drell Yan process serves as standard candle in order to identify beyond Standard Model signatures. In this talk, we plan to focus on the virtual correction to the Z-production at the order $\mathcal{O}(\alpha_s^2\alpha)$, which constitute a subset of the factorizable electroweak-QCD corrections to Drell-Yan at resonance. Our results are complete analytic, which offers advantages in multiple ways. The introduction of one electroweak gauge boson complicates the situation in many ways, from the rapid growth of the number of MIs, their evaluation to the very large analytic expression and their simplification and renormalization. Furthermore, the singlet contribution introduces different types of trace orderings, which needs very careful treatment. The talk aims to discuss the evaluation of the form-factors along with the required renormalization. Lastly we discuss the phenomenological implication of the results and outline future directions.

Speaker: Tanmoy Pati (NISER-HBNI)

10:30 AM → 12:10 PM Track 2 - Parton Showers & Matching: Parallel Session IV

Convener: Daniel Reichelt

10:30 AM Resonance aware QCD+EW MC@NLO matched parton showers

Parton showers are an essential feature of event generation that provide a numerical resummation of the large logarithms that enhance soft and collinear radiation. Matching them to higher order calculations requires careful treatment in order to avoid double-counting real radiation and preserve fixed order accuracy through matching algorithms such as MC@NLO. As we approach HL-LHC, there is a need for increasing precision of theoretical predictions so the inclusion of NLO EW alongside QCD corrections and matching to a QED shower becomes necessary. QED parton showers present addition complications, including the potential for negative splitting kernels and many more spectators to each splitting. In a dipole implementation, these spectators absorb the recoil required to satisfy momentum conservation and on-shell conditions in each splitting, however this 'reshuffling' of momenta can lead to distortion of the lineshape if it spans a resonance. Thus, the need for a resonance aware implementation is much greater for a QED shower than QCD due to the expanded set of spectators.

I will present the first implementation of automated QCD+EW MC@NLO matching in the event generator Sherpa, along with an approach to treat resonances by factorising the parton shower into production and decay for hard emissions, using Drell-Yan to illustrate the cases of both a neutral and charged resonance.

Speaker: Joanne Roper (Durham University)

10:55 AM Automated matching of a QED parton shower with NLO EW at a future lepton collider

NLO parton shower matching has been one of the triumphs of QCD research and Monte Carlo development in the past 20 years. With high-precision future electron-positron colliders planned, however, there is an urgent need for theory advances in QED and the electroweak sector. In this talk I will present an automated matching of a QED parton shower with NLO EW calculations for processes at a future lepton collider. I will introduce the MC@NLO method, then outline the challenges inherent in initial-state lepton showering and our solutions. After showing that our implementation is independent of its technical parameters, I will present results for the highly relevant process $e^+ e^- \to ZH$ at FCC-ee energies.

Speaker: Lois Flower (University of Liverpool)

11:20 AM Event isotropy in perturbative QCD

It has recently been proposed that collider events can be equipped with a metric, the Energy Mover’s Distance (EMD), which allows one to rephrase multiple aspects of jet physics in a geometric language. Further, the EMD can be exploited to define new observables that measure the distance between a given event and an idealised one. For instance, event isotropy quantifies the resemblance of an event to a uniform energy distribution. We present the first field-theoretical description of the event isotropy distribution. Our calculation includes the all-order resummation of soft and collinear logarithmic contributions at next-to-leading log accuracy, matched to next-to-leading order corrections at fixed order.

Speaker: Daniele Atzori (LPTHE Paris & INFN Genova)

11:45 AM Polarized Scattering at NLO+PS Accuracy in the POWHEG BOX

We present new Monte-Carlo tools for precision phenomenology in longitudinally polarized scattering processes, providing next-to-leading order QCD predictions matched to parton showers (NLO+PS) within the POWHEG BOX framework for di-jet production in polarized proton–proton collisions and polarized deep inelastic scattering. The generators are designed to deliver fully differential predictions for relevant observables to current and future spin-physics programs. We discuss the extensions required to consistently incorporate polarized initial states in the POWHEG formalism and study a range of observables for RHIC and for the upcoming Electron-Ion Collider. We assess the impact of parton-shower effects and selection criteria on key distributions, identifying kinematic regions where these effects are non-negligible and improve agreement with data or with higher-order predictions.

Speaker: Ignacio Borsa (Tübingen University)

12:10 PM → 2:00 PM Lunch

2:00 PM → 7:00 PM Excursion

Thu, October 8

9:00 AM → 10:45 AM Plenary

Convener: Michael Spannowsky (ITP, KIT)

9:00 AM Experimental opportunities and precision prospects at Future Colliders

Speaker: Markus Klute

9:45 AM Precision meets BSM physics

Speaker: Heidi Rzehak

10:15 AM Precision meets Effective Field Theories for BSM Physics

Speaker: Anke Biekötter (KIT ITP)

10:45 AM → 11:15 AM Coffee break

11:15 AM → 12:55 PM Track 1 - Amplitudes (process-specific): Parallel Session V

Convener: Bakar Chargeishvili

11:15 AM On non-factorizable corrections to vector boson fusion Higgs production

In this talk, I discuss non-factorizable loop contributions entering the NNLO QCD prediction for Higgs boson production via vector boson fusion at the LHC. Firstly, I present a calculation of the one-loop amplitude to higher orders in the dimensional regulator $\varepsilon$, which is required for infrared subtraction terms. Secondly, for two of the relevant two-loop five-point Feynman integral families, I discuss the construction of canonical differential equations and a first numerical implementation.

Speaker: Linus Götzfried (Universität Regensburg)

11:40 AM Analytic two-loop amplitudes for $t\bar{t}j$ production at lepton colliders

In this talk, I will present an analytic calculation of the two-loop amplitudes for $e^+e^- \to t\bar{t}j$ at leading-colour approximation. The amplitudes are decomposed into linear combinations of independent tensor structures and scalar form factors. The relevant Feynman integrals are computed analytically via the method of differential equation. After transforming the differential equations to the $\epsilon$-factorised form, the solution is expressed in terms of iterated integrals with algebraic kernels and ones that contain elliptic integrals. A library is developed to support numerical evaluations of those iterated integrals at arbitrary precisions.

Speaker: Ming-Ming Long (INFN-LNF)

12:05 PM Non-factorisable electroweak corrections at two-loop order

In view of the high-precision physics programmes of current and future collider experiments, accurate theoretical predictions for processes involving heavy unstable particles, such as the W and Z bosons or the top quark, are essential. Achieving the required level of precision demands the evaluation of two-loop corrections to the corresponding high-multiplicity and multi-scale amplitudes, whose exact computation remains extremely challenging and is often beyond the reach of current techniques. A powerful framework to address this problem is the Pole Approximation (PA), which exploits the resonant structure of the amplitude and separates higher-order corrections into two gauge-invariant classes: factorisable and non-factorisable contributions. The latter arise from soft gauge-boson exchanges and exhibit a universal structure. In this talk, we present the two-loop electroweak non-factorisable corrections to neutral- and charged-current single-resonance processes and discuss the first steps towards extending the calculation to double-resonance processes.

Speaker: Fazila Ahmadova (University of Zurich)

12:30 PM Towards NNLO QED corrections to radiative return processes

We present the analytic calculation of the two-loop QED corrections to the process $e^+e^-\to\gamma\gamma^*\to \pi^+\pi^- (\mu^+\mu^-)$, focusing on the initial-state radiation contribution, where the energetic photon is emitted from the leptonic line. The calculation is performed retaining the full dependence on all kinematic invariants, without resorting to small-mass approximations. This work is motivated by the current lack of NNLO theoretical predictions for low-energy radiative-return experiments and aims to improve the theoretical precision needed to better understand the persistent tension between experimental measurements and theoretical predictions.

Speakers: Mr Thomas Dave (University of Liverpool), Mr Pau Petit Rosas (University of Liverpool), William Torres Bobadilla (Universidad de Salamanca)

11:15 AM → 12:55 PM Track 2 - Pheno Top: Parallel Session V

Convener: Vasily Sotnikov

11:15 AM Two-loop QCD amplitudes for leading-colour ttW production at hadron colliders

In this talk I will present NNLO QCD predictions for the production of a top-antitop quark pair in association with a W boson. While results for this process have previously been obtained employing dynamical approximations for the two-loop virtual correction, this computation is based on the first direct calculation of the two-loop QCD amplitude in the leading-colour approximation. I will discuss strategies to address the complexity of the computation of the amplitude, which involves complicated analytic structures, such as nested square roots, elliptic functions, and expressions with a high degree of algebraic complexity. We express the final result in terms of a set of special functions, which we evaluate numerically through differential equations, and rational coefficients, that we evaluate via finite field techniques. Finally, I will present results for the NNLO QCD total cross section, based on an interpolation grid for the two-loop finite remainder.

Speaker: Mattia Pozzoli (University of Bologna and INFN)

11:40 AM NNLO QCD Predictions for Top-Quark Pair Production in Association with a Jet at the LHC

I will present next-to-next-to-leading-order (NNLO) QCD predictions for top-quark pair production in association with a jet at the LHC. I will first describe the computation of the two-loop scattering amplitudes in the leading-colour approximation and discuss the impact of the higher-order corrections on the total cross section and selected differential distributions.

Speaker: Heribertus Bayu Hartanto (Asia Pacific Center for Theoretical Physics)

12:05 PM Two-loop QCD amplitudes for qq->ttH production in the generalised leading-colour limit

The production of a top–antitop quark pair in association with a Higgs boson (ttH) is a crucial process at the Large Hadron Collider (LHC), as it provides a direct probe of the top-quark Yukawa coupling. Previous phenomenological results for this process have relied on dynamical approximations to the two-loop virtual corrections, while the amplitudes themselves have not yet been calculated directly. In this talk, I will present the first direct computation of the two-loop amplitudes for the quark-initiated channel of ttH production in the generalised leading-colour limit. I will discuss the computational strategies employed and present the preliminary results obtained.

Speaker: Dr Xiang Chen (University of Zurich)

12:30 PM Two-loop Feynman integrals for $t \bar{t} \gamma$ hadron production in the leading colour approximation

In this talk, I will present the calculation of the Feynman integrals entering the two-loop scattering amplitudes for top–antitop pair production in association with a photon, in the leading-colour approximation, required for NNLO QCD predictions at hadron colliders.
The kinematics of the process, involving six independent invariants and up to three massive propagators, leads to a high degree of algebraic and analytic complexity, with several sectors featuring nested square roots and elliptic integrals.
Using finite-field techniques, we reconstruct the differential equations satisfied by a suitable basis of master integrals that we identify. We define a set of special functions in terms of which all master integrals can be expressed, and solve their differential equations numerically.

Speaker: Colomba Brancaccio (University of Turin)

11:15 AM → 12:55 PM Track 3 - Precision Physics / BSM: Parallel Session V

Convener: Matthias Kerner (KIT)

11:15 AM Higgs boson decay to massive bottom quarks at $\mathcal{O}(\alpha_s^4)$

The decay into bottom quarks is the dominant decay channel of a Standard Model Higgs boson. Its precise theory description is crucial for extracting the bottom quark Yukawa coupling and mass from experimental measurements. The decay width has been computed through $\mathcal{O}(\alpha_s^4)$ assuming massless final states.
We report on the status of the corresponding four-loop calculation retaining the mass of the bottom quark. In particular, we focus on the contribution originating from the top quark Yukawa coupling induced process. The impact on the decay width due to different renormalization schemes for the Yukawa coupling and mass of the bottom quark is examined.

Speaker: Marco Niggetiedt (University of Zurich)

11:40 AM Taking the First Steps Toward Higgs Production at N4LO in QCD

We present recent progress toward the inclusive gluon-fusion Higgs-boson and Drell–Yan cross sections at next-to-next-to-next-to-next-to-leading order (N4LO) in perturbative QCD. Our main results concern the single-real contributions, involving three QCD partons together with a Higgs boson or virtual photon. These comprise the interference of one- and two-loop amplitudes and, in the generalized leading-color limit, the interference of tree-level and three-loop amplitudes. The results are expressed as Laurent expansions in the dimensional regulator ($\epsilon$), with coefficients given by analytic functions of the ratio of the color-singlet invariant mass to the partonic center-of-mass energy.
We also discuss recent progress on the double-real-emission contributions in the strict threshold limit, providing further ingredients toward a complete N4LO prediction. Beyond their phenomenological relevance, these calculations offer a laboratory for studying analytic complexity that arises at high perturbative order.

Speaker: Adi Prasanna Suresh (SLAC and Stanford U.)

12:05 PM Two-loop mixed QCD-EW corrections to quark-induced Higgs production at hadron colliders

We present the exact next-to-leading-order QCD corrections to the light-quark part of the mixed QCD-EW contributions to quark-induced Higgs production at the Large Hadron Collider, for a center-of-mass energy of 13 TeV, with exact EW-boson mass dependence. The relevant two-loop real-emission matrix elements, $gq(\overline{q})\to q(\overline{q})H$ and $q\overline{q}\to gH$, are computed using one-dimensional series expansion strategy together with spline interpolation. A phenomenological study of the total cross-section and the Higgs $p_T$ distribution is presented.

Speaker: Federico Ripani

12:30 PM Renormalization of the general Two-Higgs-Doublet Model

Fully exploiting the precision of current and future collider measurements requires theory predictions of matching accuracy, and hence observables computed at next-to-leading order (NLO) and beyond. For any Beyond-the-Standard-Model scenario, such higher-order calculations require a complete and consistent renormalization of the model. We address this task for the general Two-Higgs-Doublet Model (THDM), a well-motivated extension that enlarges the scalar sector to five physical states with a rich collider phenomenology. Whereas existing NLO calculations have focused almost exclusively on symmetry-constrained versions, we consider the most general THDM, which encodes all constrained types as special cases and can act as an effective field theory of many UV-complete models. We introduce our choice of physical input parameters and renormalization conditions, and, using Higgs-to-Higgs and Higgs-to-fermion decays at NLO as example processes, discuss criteria for selecting renormalization schemes with fast perturbative convergence.

Speaker: Martin Gabelmann (U. Freiburg)

12:55 PM → 2:15 PM Lunch

2:15 PM → 3:45 PM Plenary

Convener: Mathieu Pellen

2:15 PM Recent developments in PDFs

Speaker: Juan Rojo

2:45 PM Precision meets Machine Learning

Speaker: Daniel Maitre

3:15 PM Quantum Machine Learning for Particle Physics

Speaker: Michael Spannowsky (ITP, KIT)

3:45 PM → 4:15 PM Coffee break

4:15 PM → 6:20 PM Track 1 - Amplitudes (process-specific): Parallel Session VI

Convener: Simone Zoia

4:15 PM Two-loop QCD corrections for Higgs plus two-jet production through gluon fusion

We present two-loop scattering amplitudes in QCD for the hadronic production of a Higgs boson in association with two jets mediated by the top-quark Yukawa coupling.
Our results cover the dominant contributions for all partonic channels, which are computed in the heavy top-mass limit in the leading-color approximation.
We obtained analytic expressions of the amplitudes decomposed in an integral basis by reconstructing the integral coefficients from numerical evaluations in finite fields.
To handle the amplitudes' complexity, we exploited their analytic properties, reducing the required number of samples for the reconstruction and leading to compact representations.
Finally, we studied the singularity structure of the amplitudes and find surprising non-analytic behaviour in the bulk of the physical phase space.

Speaker: Viktor Kuschke (PSI, UZH)

4:40 PM Analytic form of the elliptic master integrals for gg->hg at two loops

We present our analytic calculation of the master integrals for gg->gh at 2-loops with internal top quarks, considering the planar elliptic family. We bring the system of differential equations into the epsilon-factorised form using transformations involving elliptic integrals. We present our approach to find a suitable variable change from the kinematic space to the punctured torus. Using this, we write the differential equations in terms of Kronecker-Eisenstein forms and the resulting iterated integrals in terms of elliptic Multiple Polylogarithms (eMPLs).

Speaker: Bakul Agarwal (University of Edinburgh)

5:05 PM NLO corrections to inclusive $\bar{B} \to X_s \gamma$ decays at subleading power

Theoretical predictions in hadron physics are often limited by non-perturbative uncertainties in QCD. Nevertheless, several phenomenologically important processes require improved theoretical control. Effective field theories, such as Soft-Collinear Effective Theory (SCET) and Heavy Quark Effective Theory (HQET), provide powerful tools to overcome these limitations by exploiting factorisation.
A particularly interesting class of observables arises in flavour physics, and in particular in inclusive $B\to X_s\gamma$ decays. Among the resolved contributions to this process, the dominant theoretical uncertainty currently originates from the interference between the WET operators $Q_1^q$ and $Q_{7\gamma}$, which corresponds to a non-local subleading power corrections.
In this work, we derive a factorisation formula for this interference that is suitable for the inclusion of perturbative corrections. The factorised expression involves four distinct functions. We present explicit results for all of them, with particular emphasis on the renormalisation-group evolution of the shape function $g_{17}$, a generalised light-cone distribution amplitude depending on both light-cone directions, and the two-loop penguin jet function, which was computed fully analytically.
These ingredients complete the NLO corrections to the $Q_1^q-Q_{7\gamma}$ interference. Moreover, they provide important insight into the technical structure of these higher-order corrections. These results are expected to be highly relevant for future precision studies at subleading power.

Speaker: Riccardo Bartocci (KIT (Karlsruhe Institute of Technology))

5:30 PM FeynGraph - A Modern High-Performance Feynman Diagram Toolkit

We present FeynGraph, a modern high-performance Feynman diagram generation toolkit designed to integrate seamlessly with modern computational workflows for calculating scattering amplitudes. FeynGraph is designed as a high-performance Rust library with easy-to-use Python bindings, allowing it to be readily used in other tools. With additional features like custom diagram selection filters, automatic diagram drawing and soon automatic amplitude construction, FeynGraph strives to be a fully-featured Feynman diagram toolkit at any loop order.

Speaker: Jens Braun (Institute for Theoretical Physics (ITP))

5:55 PM Two-Loop Electroweak Renormalization in the Standard Model and NNLO Corrections to $H\to b\bar{b}$

Next-generation high-energy colliders, including the HL-LHC, and proposed Higgs factories such as FCC-ee, ILC, and CEPC, aim to probe selected Higgs and electroweak observables at the per-mille level. Achieving the required theoretical precision demands NNLO electroweak predictions alongside high-order QCD corrections. However, complete NNLO EW calculations in the SM remain scarce, with a key bottleneck being the absence of a complete and reusable two-loop EW renormalization framework.

In the first part of this talk, I will present our progress toward constructing and validating a complete two-loop on-shell EW renormalization framework for the SM. The discussion will cover mass, field, mixing, and charge renormalization constants, together with sub-loop renormalization, electroweak input schemes, and the treatment of unstable particles.
The second part will focus on the framework’s first phenomenological application: the pure NNLO EW and mixed QCD-EW corrections to the fully inclusive decay width of the Higgs decay proccess $H\to b\bar b+X$. I will discuss the numerical impact and interplay of these corrections, examine their dependence on the EW input scheme, and compare independent implementations in the Feynman–'t Hooft and Landau gauges.

Speaker: Zhe Li (Shandong University)

4:15 PM → 6:20 PM Track 2 - Pheno Top: Parallel Session VI

Convener: Stefano Pozzorini

4:15 PM Hadron Fragmentation at Past, Present and Future Colliders

The production of identified hadrons in collider experiments provides a unique window into Quantum Chromodynamics (QCD) across a wide range of energy scales.
Precision measurements at past, present, and future colliders increasingly demand equally precise theoretical predictions, requiring the interplay of perturbative calculations and global analyses of non-perturbative inputs.
Most calculations to date have been performed in a semi-inclusive manner, while more exclusive observables require their implementation in fully differential frameworks.
We present the calculation of NNLO corrections to hadron-in-jets observables for 2- and 3-jet events at e+e- colliders.
We further discuss the calculation of identified-hadron processes at lepton--proton and proton--proton colliders within the NNLOJET framework.

Speaker: Francesco Merlotti (ETH Zürich)

4:40 PM A first extraction of gluon TMDs at N3LL from Higgs data

We present the first extraction of the unpolarised gluon transverse-momentum-dependent (TMD) parton distribution from Higgs-boson production data at the LHC.
The analysis is based on the currently available set of ATLAS and CMS measurements of the Higgs qT distribution at √s= 8 and 13 TeV in the diphoton and four-lepton decay channels.
Theoretical predictions are computed up to N3LL accuracy, with the contribution of the linearly polarised gluon accounted for.
Fiducial selections are consistently incorporated for both two-(diphoton) and four-body (four-lepton) final states.
The fit reproduces both the shape and the normalisation of the experimental data, and yields a moderate sensitivity to the nonperturbative content of gluon TMDs.
We further assess the convergence of the perturbative expansion and the stability of the extracted distribution under variations of the qT cut.
This analysis provides a baseline for future extractions combining LHC Higgs measurements with other gluon-sensitive processes spanning a broader range of hard scales.

Speaker: Giuseppe Bozzi (University of Cagliari and INFN, Cagliari)

5:05 PM Stable NNLO QCD predictions for quarkonium production and decay

Perturbative instabilities at next-to-next-to-leading order (NNLO) have become a recurring challenge in theoretical predictions for quarkonium production and decay within the NRQCD framework, often leading to large corrections, enhanced scale dependence, or even unphysical negative cross sections and decay widths. In this talk, I will present our recent work addressing the origin of these instabilities. By consistently incorporating the perturbative soft contributions to the quarkonium wave function at the origin, NNLO predictions exhibit improved perturbative convergence and become independent of the NRQCD factorization scale at this order. The proposed framework is applied to a wide range of S-wave color-singlet production and decay processes, yielding substantially improved agreement with experimental measurements and providing a robust foundation for future precision studies of heavy quarkonium.

Speaker: Luca Maxia (LPTHE - CNRS et Sorbonne Université)

5:30 PM Amplitude Factorization Prescription for Exclusive Processes and NNLO Application to Quarkonium $\to 3\gamma$ Decay

We address the long-standing problem of negative decay and production rates in perturbative QCD for exclusive processes by proposing amplitude-level NRQCD factorization as a systematic prescription. Building on this, we present the first complete next-to-next-to-leading-order (NNLO) QCD correction to the decay $J/\psi \to 3\gamma$. The resulting partial width, $\Gamma(J/\psi \to 3\gamma) = 0.96^{+4.32}_{-0.13}$ eV, combines this NNLO contribution with the known up to $\mathcal{O}(\alpha_s v^2)$ relativistic correction and shows markedly improved agreement with the high-precision BESIII measurement. In the same way, $\Gamma(\Upsilon \to 3\gamma) = 0.0086^{+0.0028}_{-0.0006}$ eV is obtained.

From a first-principles perspective, it is clear that for exclusive processes, taking the complete modulus squared of the full amplitude is precisely the proper definition of the probability distribution and guarantees its manifest positivity. This makes the amplitude-level prescription the natural and physically motivated scheme. For inclusive processes, however, one is forced to abandon the full modulus square due to the need to cancel infrared divergences at the level of the truncated squared amplitude.

Based on arXiv:2603.26199.

Speaker: Jianxiong Wang (Institute of High Energy Physics, Chinese Academy of Science)

5:55 PM DIS-secting the universe with high-energy neutrinos

We revisit the impact of electroweak (EW) radiative corrections on the kinematic distributions of charged leptons in neutrino-induced Charged-Current (CC) Deep Inelastic Scattering (DIS). We implement full Next-to-Leading Order (NLO) EW corrections to CC DIS in a flexible Monte Carlo framework, supplemented with higher-order logarithmically enhanced final-state QED radiation. We compare our results to exclusive NLO QCD plus Parton Shower (PS) predictions obtained with an existing POWHEG-BOX-RES event generator, examining different PS models and settings. Based on this comparison, we provide recommendations for the use of the POWHEG-BOX event generator in experimental analyses. We further assess the impact of radiative corrections on the correlation between the observed muon energy and the incoming neutrino energy for a realistic astrophysical neutrino flux.
These corrections can exceed 10%, yet they are reliably described across several orders of magnitude in energy.

Speaker: Lorenzo Guerra (Max Planck Institute for Physics)

4:15 PM → 6:20 PM Track 3 - Precision Physics / BSM: Parallel Session VI

Convener: Heidi Rzehak

4:15 PM Next-to-Leading-Order QCD and EW Corrections to the Dark Matter Relic Density in the Framework of the CxSM

This talk presents the computation of the next-to-leading-order (NLO) QCD and electroweak (EW) corrections to the annihilation of dark matter particles into the dominant final states, processes that play a key role in determining the dark matter relic density. The analysis is performed within the Complex Singlet Extension of the Standard Model (CxSM), which enlarges the Standard Model scalar sector by a complex singlet field and provides a viable dark matter candidate. The treatment of the ultraviolet (UV) and infrared (IR) divergences encountered in the calculation is briefly discussed. The relic density is evaluated at NLO accuracy, and the impact of the QCD and EW corrections on the final prediction is examined together with its phenomenological implications.

Speaker: Karim Elyaouti (KIT - Institut für Theoretische Physik)

4:40 PM ZH production in gluon fusion at NLO QCD within SMEFT

Gluon-induced production of a Higgs boson in association with a Z-boson is an important Higgs production channel at the LHC. Precise theoretical predictions for this channel are therefore required, both within the Standard Model and beyond. Effects beyond the SM can be parametrized using the Standard Model Effective Field Theory (SMEFT).
In this talk, we present the NLO QCD predictions for including fully analytic top-mass-dependence. We incorporate the leading dimension-six SMEFT operators relevant for this process. We study their phenomenological impact and the interplay of the Wilson coefficients, based on an implementation in Powheg-Box-V2.

Speaker: Benjamin Campillo (KIT)

5:05 PM Higgs Mass Predictions in the CP-Violating High-Scale NMSSM

In a supersymmetric theory, large mass hierarchies can lead to large uncertainties in fixed-order calculations of the SM-like Higgs mass. Reliable predictions in an effective field theory (EFT) framework involve the matching to the full supersymmetric theory at the high scale to include contributions from the heavy particles, and a subsequent renormalization-group running down to the low scale.

In my talk, I discuss the prediction of the SM-like Higgs mass within the CP-violating Next-to-Minimal Supersymmetric extension of the SM (NMSSM) in a scenario where all non-SM particles feature TeV-scale masses. The matching conditions are calculated at full one-loop and implemented in the public program package NMSSMCALC using two approaches, the matching of the quartic Higgs couplings as well as of the SM-like Higgs pole masses of the low- and high-scale theory. A comparison between the two methods allows for an estimate of the size of terms suppressed by the heavy mass scale that are neglected in a pure EFT calculation. I furthermore report on the progress of the two-loop calculation for the pole-mass matching.

Speaker: Dr Christoph Borschensky (Karlsruhe Institute of Technology)

5:30 PM NNLO QCD predictions for identified hadron production in association with neutral electroweak gauge bosons.

Identified hadron production in association with an electroweak gauge boson provides a powerful probe of QCD dynamics and hadron fragmentation in proton-proton collisions. We present next-to-next-to-leading-order (NNLO) QCD predictions for the associated production of a neutral electroweak gauge boson and an identified hadron at high energy colliders. The calculation employs the antenna subtraction formalism, consistently accounting for fragmentation contributions at NNLO. Phenomenological predictions are presented for fragmentation-sensitive observables, and the impact of the NNLO corrections for the perturbative convergence and theoretical precision of the predictions is investigated by comparing those with experimental data.

Speaker: Gabriele Fiore (ETH Zurich)

5:55 PM Reconstructing distributions from Monte-Carlo simulations using orthogonal basis functions

Reconstruction of distributions from Monte-Carlo simulations is a standard problem in high-energy physics.
Traditionally, this is done by collecting the generated events in histograms. I will present an alternative approach, the main idea of which is to approximate the target distribution as a sum of orthogonal basis functions with coefficients that are given by certain moments of the target distribution, which are calculated using the Monte-Carlo integration. This method has the advantage of directly yielding smooth approximations to target distributions, and, in the context of perturbative calculations with local subtractions, it protects against so-called bin-to-bin fluctuations, which often severely affect the quality of conventional histograms. I will propose a prescription for truncation of the functional expansion and a method for estimating the Monte-Carlo and truncation errors. I will also discuss how an initial approximation to the target distribution, such as a leading-order result, can be used to construct an orthonormal basis that is optimized for the specific distribution.

Speaker: Ivan Novikov (KIT)

7:00 PM → 11:59 PM Conference Dinner

Höpfner Brewery, Schalander Room, Haid-und-Neu-Strasse 18

Fri, October 9

9:00 AM → 10:40 AM Track 1 - Amplitude (generic): Parallel Session VII

Convener: Kirill Melnikov (TTP KIT)

9:00 AM OpenLoops+LTD: new developments at NLO and beyond

OpenLoops+LTD is a new automated NLO parton-level generator that combines aspects of the Loop-Tree Duality technique with the OpenLoops approach. The first part of the talk deals with methodological aspects, with focus on double and triple-cut singularities and local IR cancellations. This is complemented by first NLO QCD results for multi-jet plus multi-boson production at electron-positron colliders. The second part of the talk deals with the latest developments of our new Loop-Loop Duality approach, which automates two-loop calculations by injecting analytic one-loop subdiagrams into the numerical one-loop diagrams that are integrated through the OpenLoops+LTD algorithm.

Speaker: Nicolo Giraudo (University of Zurich)

9:25 AM Local factorisation of arbitrary two-loop QED amplitudes

We present an integrand-level representation of generic two-loop amplitudes in massless Quantum Electrodynamics (QED) that is free of IR singularities. We define building blocks that render the integrand manifestly polarised and Ward-identity preserving, in such a way that spurious (transient) singularities are removed. The full integrands are then assembled by gluing these building blocks together according to specific prescriptions that cure the additional transient singularities arising in the process. We present the locally UV-renormalised, IR-subtracted amplitude for generic two-loop QED processes, together with insights on possible extensions beyond two loops. This work can be regarded as a step towards an extension to QCD amplitudes with jets in the final state.

Based on a work in collaboration with C. Anastasiou, A. Favorito, G. Gambuti, R. Sahoo, G. Sterman

Speaker: Christian Biello (ETHZ)

9:50 AM Acyclicity, causality and infrared singularities

One of the main strengths of the Loop-Tree Duality representation of scattering amplitudes is that it provides a particularly transparent description of the origin of infrared singularities. This talk will review recent progress in elucidating how infrared singularities emerge and cancel at the level of vacuum amplitudes, how finite integrals can easily be constructed, and will also present a complementary approach based on encoding the underlying causal and singular structure in terms of qubits and quantum circuits.

Speaker: Germán Rodrigo (IFIC UV-CSIC)

10:15 AM The software stack behind Local Unitarity and how it can help you too

Speaker: Valentin Hirschi

9:00 AM → 10:40 AM Track 2 - High energy: Parallel Session VII

Convener: Marco Niggetiedt

9:00 AM Top quark mass effects in WW production through gluon fusion

The di-boson WW production is an important process for the precision tests of the Standard Model at the electroweak scale. In addition, it is one of the most significant backgrounds in the H→WW decay. While the gluon fusion production channel contributes only around 5% of the cross section, it is expected to receive sizable QCD corrections that will become significant during the High Luminosity phase of the LHC program. Moreover, its relative size is enhanced in the fiducial region of the H→WW decay. In this talk, I will discuss the computation of the helicity amplitudes of the gg→WW scattering. In particular, three different expansions of the amplitudes will be described,
including their applicability to different regions of the phase-space
and the methods employed for their analytic calculation.

Speaker: Mateusz Pawel Czaja (KIT TTP)

9:25 AM The emerging importance of high energy logarithms for LHC studies

In this talk, I will discuss the growing importance of controlling high-energy logarithms in predictions for LHC processes. In a recent ATLAS measurement [arXiv:2403.02793], state-of-the-art matched parton-shower predictions for a hard photon or an electroweak
vector boson in association with at least two jets (pp→{γ,Z,W}+jj) deviate systematically from data as the partonic collision energy grows. This effect is due to the dominance of high-energy logarithms, which spoil the convergence of the fixed-order perturbative series and
are captured to all orders by the framework of High Energy Jets. I will present new results for Z+dijets, which show that all-order resummation resolves the discrepancies. I will also highlight the importance of high-energy logarithms in Higgs boson plus quark-pair
production as a background to di-Higgs searches, and in isolated photon plus jets production.

Speaker: Sebastian Jaskiewicz (Bern U.)

9:50 AM ggxy: Fast and flexible NLO QCD corrections to ZH and VV in gluon fusion

We present the C++ library ggxy, which can be used for the fast and flexible calculation of partonic and hadronic cross sections to gluon-initiated top-mediated processes such as $gg\to HH$. We have extended the functionality of ggxy with the implementation of the $gg\to ZH$ and $gg\to VV$ processes. While all other parts are exact, the two-loop amplitudes with internal top quarks have been computed using analytical approximations that are valid in two opposite phase-space regions and together cover the full phase space. The expressions are ideal for a fast and numerically stable evaluation, while retaining the full dependence on all input parameters. This allows for a fast and flexible calculation of the NLO QCD corrections to $gg\to ZH$ and $gg\to VV$ with full top-quark mass dependence.

Speaker: Daniel Stremmer (KIT)

10:15 AM Three-loop QCD corrections to gg->HH at leading power in the high-energy limit

We report progress toward understanding quark-mass effects in the (gg \rightarrow HH) amplitude at NNLO, at leading power in the high-energy limit (s, |t|, |u| \gg m_t^2 \gg m_H^2). The logarithmic behavior of this process in this regime has recently been shown to follow a predictable, factorized pattern at leading power. We present results for the three-loop virtual QCD corrections in this limit. Together with the systematic inclusion of top-quark mass dependence through the running of the coupling and the massification procedure, these results will allow us to capture the dominant logarithmic contributions in the top-quark mass expansion at very high energies. These developments improve the theoretical prediction for (gg \rightarrow HH) at NNLO and, when combined with the real-real and real-virtual contributions, have the potential to reduce the associated mass-scheme uncertainty.

Speaker: Ajjath A H (IISc, Bangalore, India)

10:40 AM → 11:10 AM Coffee break

11:10 AM → 1:35 PM Plenary

Convener: Thomas Becher (Universität Bern)

11:10 AM The two-loop pentagon frontier

Speaker: Simone Zoia (University of Zurich)

11:40 AM Numerical Methods and Phenomenological Applications

Speaker: Stephen Jones (IPPP Durham)

12:10 PM Closing Talk

Speaker: Thomas Gehrmann

12:55 PM Farewell