Numerical Perturbation Theory

Contribution List

3. Applications and challenges in numerical methods for pQFT

Valentin Jonathan Hirschi (University of Bern)

20/11/2025, 09:00

Morning 1

I will briefly present a [recent application][1] of [Local Unitarity][2] to the calculation of the NNLO QCD correction to $\gamma \gamma \rightarrow Q \bar{Q}$.

Local Unitarity is a computational technique achieving the local cancellation of infrared singularities at the integrand level, unlocking the computation of perturbative cross-section fully numerically in momentum space.

This...

5. The art of constucting and sampling cut integrals

Mathijs Fraaije (University of Bern)

20/11/2025, 09:25

Morning 1

This talk will introduce new Monte Carlo sampling techniques used for the numerical integration of momentum-space loop integrals in the Loop-Tree Duality (LTD) framework.

I will then discuss the factorization property of the Cross-Free-Family (CFF) representation of LTD and how it can be used to conveniently construct three-dimensional integrands of cut diagrams.

4. Localized renormalization and graph-based tooling

Lucien Huber (University of Bern)

20/11/2025, 09:50

Morning 1

The BPHZ formalism provides a systematic framework for subtracting ultraviolet divergences from Feynman graphs. Originally conceived as a purely theoretical construct, it now underpins the ultraviolet regularization strategy for Local Unitarity, as implemented in gammaloop, an upcoming program designed to compute perturbative cross-sections fully numerically in momentum space.

In this talk,...

9. Off-shell triphoton production via quark loops: Threshold subtraction and multi-channel Monte Carlo

Dario Kermanschah (ETH Zürich)

20/11/2025, 10:40

Morning 2

I will give an overview of our approach for the direct numerical integration of two-loop corrections to electroweak production. After subtracting infrared and ultraviolet singularities, we enable numerical integration in momentum space through analytic integration over the energy components of the loop momenta, subtraction of threshold singularities, and the use of importance sampling with the...

10. Colorless final-state production via $q\bar{q}$ annihilation at two-loops: the fermion loop contributions and beyond

Matilde Vicini (ETH Zürich)

20/11/2025, 11:05

Morning 2

We present recent advances in the numerical integration of two-loop scattering amplitudes for the production of 2 and 3 vector bosons via quark-antiquark annihilation. The numerical integration is performed in loop momentum space in four spacetime dimensions. This is made possible by the simultaneous local subtraction of infrared, ultraviolet, and threshold singularities (more details are...

1. Factorisable Local Unitarity for Hadronic Cross-Sections

Zeno Capatti (University of Bern)

20/11/2025, 13:30

Afternoon 1

The KLN theorem establishes that infrared divergences in parton‑model diagrams cancel when summed alongside diagrams that account for the simultaneous hard interaction of multiple partons within the same hadron. Meanwhile, it is well established that initial-state infrared poles and logarithms are governed by collinear factorisation. In this talk, I introduce a formalism where an initial-state...

6. Loop–Tree Duality at Finite Temperature and Density

Kaapo Elmo Ilmari Seppänen (University of Bern)

20/11/2025, 13:55

Afternoon 1

In finite-temperature or finite-density QFT, computing perturbative coefficients is notoriously challenging because the thermal bath breaks Lorentz symmetry by singling out the time direction, making standard integration-by-parts and differential-equation techniques inefficient. I will present the generalization of Loop–Tree Duality (LTD) to thermal settings, in which loop-energy (Matsubara)...

15. Soft Factorisation and Exponentiation from Schwinger-Space Geometry

Giulio Gambuti (University of Oxford)

20/11/2025, 14:20

Afternoon 1

In this talk I will report on a recent analysis of soft divergences of entire scattering amplitudes within the Schwinger-parameter representation of Feynman integrals. Using tools from tropical geometry and graph theory, I will show how soft and hard contributions factorise directly in parameter space and how “worldline” Schwinger variables make exponentiation of soft divergences manifest at...

12. bbH production: a theoretical laboratory for flavour-scheme studies

Christian Biello (Max-Planck Institute for Physics)

20/11/2025, 15:10

Afternoon 2

We present NNLO QCD predictions for Higgs boson production in association with a bottom-quark pair, matched to parton showers. This process provides a unique testing ground for precision QCD and flavour-scheme studies, as the presence of bottom quarks makes it suitable for investigating mass effects and factorisation schemes. In the collinear heavy-quark factorisation approach (5FS),...

8. Locally finite two-loop amplitudes for photoproduction in quark annihilation

Roshni Sahoo

20/11/2025, 15:35

Afternoon 2

Precise predictions for increasingly complex processes at higher perturbative orders call for a process-independent algorithm that can numerically integrate multi-loop amplitudes directly in momentum space. However, Feynman amplitudes are plagued by infrared and ultraviolet singularities which must be removed at the integrand level before numerical integration can be performed. In recent...

14. Locally finite QCD amplitudes and cross sections

Julia Karlen (ETH Zurich)

20/11/2025, 16:00

Afternoon 2

In this talk I will present a framework for local subtractions of infrared singularities in hadron collider cross sections and amplitudes. The construction is guided by infrared factorization and leads to integrands in loop momentum and phase space that are suitable for integration via numerical methods.

I will focus on electroweak production via quark–antiquark annihilation at NNLO. To...

13. Numerical Evaluation of the Two-Loop Dark Matter Power Spectrum in the EFTofLSS

Andrea Favorito (ETH Zürich)

20/11/2025, 16:25

Afternoon 2

This talk focuses on the application of modern numerical perturbative methods, familiar from collider physics, to the precision frontier of cosmology. To match the accuracy of modern cosmological surveys, theoretical predictions from the Effective Field Theory of Large-Scale Structure (EFTofLSS) must be pushed to the two-loop level, a task for which purely numerical techniques are essential...