Danish Quantum Field Theory Meeting 2025

13 Aug 2025, 09:30 → 14 Aug 2025, 16:00 Europe/Copenhagen

U220 (University of Southern Denmark)

From August 13-14, 2025, the Danish Quantum Field Theory Meeting 2025 will take place at the University of Southern Denmark, Odense. The aim of the meeting is to bring together researchers from Denmark and beyond working on various aspects of Quantum Field Theory. Topics will include scattering amplitudes, gravitational waves, gauge-gravity correspondence, string theory, mathematical physics, topological Quantum Field Theory, phenomenology and lattice Quantum Field Theory.

Registration for the event is open. As part of the registration, please indicate if you would like to contribute a presentation. If you register for the meeting, please be aware that there is only a limited number of seats in the room and we may not be able to accept all registrants. Please note that your participation is not confirmed, until you receive a confirmation email. 

The registration deadline for contributing presentations was June 30th, 2025.

The registration deadline for participation was July 31st, 2025.

Invited speakers 

• Emil Bjerrum-Bohr
• Hjalte Frellesvig
• Benjamin Jäger
• Niels Obers
• Marta Orselli
• Alessia Platania
• Konstantin Wernli

 

Organizers

• Roger Morales
• Florian Seefeld
• Matthias Wilhelm

 

Logistics

Anne Katrine Birch - birch@imada.sdu.dk

 

Sponsors

Poster.pdf

Wednesday 13 August

09:30 → 10:00 Registration and coffee

10:00 → 10:45 Dynamics in Classical Gravity from Scattering Amplitudes

Speaker: Emil Bjerrum-Bohr

emilbb.pdf

10:45 → 11:30 3-body systems in strong-gravity

I will present a novel approach to study the dynamics of 3-body systems in a regime of strong gravity, going beyond the point-particle description typically used in the literature. Among other things, I will show how the inclusion of strong-gravity effects from a third body can significantly reduce the merger time of a binary system, affecting also the emitted gravitational wave signal. I will apply this approach to study the so-called precession resonances, revealing that, including strong gravitational effects, one obtains a richer physics for the system under investigation.

Speaker: Marta Orselli

Marta Orselli Talk - Odense.pdf

11:30 → 12:00 Kerr Black Hole Dynamics from an Extended Polyakov Action

We examine a hypersurface model for the classical dynamics of spinning black holes. Under specific rigid geometric constraints, it reveals an intriguing solution resembling expectations for the Kerr Black three-point amplitude. We explore various generalizations of this formalism and outline potential avenues for employing it to analyze spinning black hole attraction.

Speaker: Gang Chen

KerrActionDSU.pdf

12:00 → 13:00 Lunch break

13:00 → 13:30 Perturbative Computations from Curved Spacetimes

Given the impressive results for classical observables obtained by field theoretic approaches to gravitational systems, we can ask if these tools can help us in new regimes and problems of interest. Amplitude tools are particularly well suited to derive observables for the binary system in a post-Minkowskian expansion, where they have achieved complete results to fourth order in Newton's constant. However, obtaining strong field results is a complicated problem. From the perspective of perturbative quantum field theory, classical solutions in general relativity are remarkable objects; they make manifest a resummation of an infinite series of Feynman diagrams encoding information to all orders in Newton’s constant. I will describe an effective field theory formalism tailored for computations about nontrivial classical backgrounds, and present the potential, and hurdles, in combining advantages from classical gravitational and field theoretic techniques to address questions related to the binary inspiral problem.

Speaker: Nabha Shah

13:30 → 14:15 Perturbative TQFTs

Topological Quantum Field Theories (TQFTs) were axiomatized by Atiyah as symmetric monoidal functors whose domain is a cobordism category. On the other hand, recently developed methods allow for perturbative quantization of field theories on manifolds with boundary. I will review these concepts and then sketch a research program to build a bridge between them, discussing the example of Chern-Simons theory in some detail. One of the goals of this activity is to open new avenues towards the Asymptotic Expansion Conjecture.

Speaker: Konstantin Wernli

konstantin.pdf

14:15 → 14:45 Resurgence in Topological Quantum Field Theory

Resurgence is a method for summation of divergent power series. In recent years this have been succesfully applied to divergent series arising from pertubation theory in quantum field theory. I will illustrate this with the Witten-Reshetikhin-Turaev topological quantum field theory for a certain general class of three-manifold space-times. This is based on joint work with Andersen, Han, Li, Sauzin and Sun.

Speaker: William Mistegård

WEM.SDU.13.08.2025.pdf

14:45 → 15:15 Coffee break

15:15 → 16:00 A BPS Road to Holography: Decoupling Limits and Non-Lorentzian Geometries

I will discuss decoupling limits that lead to matrix theories on D-branes, focusing on their BPS nature and the emergence of non-Lorentzian target space geometries. In these limits, D-branes experience instantaneous gravitational forces, and when applied to curved geometries, it is shown that a single decoupling limit leads to the AdS/CFT correspondence. By applying two such limits, we generate new holographic examples, including those with non-Lorentzian bulk geometries. I will demonstrate that reversing these decoupling limits corresponds to deformations of matrix theories, connecting them to the TTbar deformation in two dimensions. These deformations provide a new perspective on the near-horizon brane geometry and lead to TTbar-like flow equations for the Dp-brane DBI action. Finally, I will comment on a wider duality web, that exhibits relationships between matrix theories, non-relativistic string theory, M-theory uplifts along with corners that connect dS holography to Carrollian symmetry.

Speaker: Niels Obers

BPSholo_Odense_2025.pdf

16:00 → 16:30 Boundary energy-momentum tensor for asymptotically flat spacetimes

I will discuss the construction of a boundary energy-momentum tensor for asymptotically flat spacetimes. This involves rewriting Einstein's equations in a way that is covariant with respect to the Carrollian boundary geometry and turns part of the Einstein equations into Ward identities for the Carrollian energy-momentum tensor. I will also discuss holographic renormalisation for asymptotically flat spacetimes. This provides new insights into a putative holographic description of flat spacetime in terms of a boundary Carrollian conformal field theory.

Speaker: Emil Have

Presentation_Odense.pdf

16:30 → 17:00 Integrable corners in the space of Gukov-Witten defects

Integrability of planar N=4 super-Yang-Mills (SYM) theory enables exact computations of unprotected observables, even with the insertion of certain extended operators. While integrability techniques have been successfully applied to some supersymmetric domain walls and line defects, it is an open question whether there are any integrable surface defects in N=4 SYM theory. In this talk, I will examine a class of 1/2-BPS surface defects known as Gukov-Witten defects. I will argue that these defects are generically not integrable but they are likely to become integrable at a corner in parameter space. I will present closed-form factorised expressions for leading-order one-point functions of unprotected scalar operators, hinting at the possibility of finding an all-loop formula at this special point.

Speaker: Adam Chalabi

Gukov-Witten talk.pdf

18:30 → 20:30 Conference dinner - Storms Pakhus

Thursday 14 August

09:00 → 09:45 Amplitudes, intersection theory, and Higgs physics

In this presentation I will first introduce my own perspective on the field of amplitudes and how it is related to the rest of particle physics.
Secondly I will describe my own work in that area, primarily focusing on two topics: the connection between Feynman integrals and the mathematical field of intersection theory, as well as the particle phenomenology of the Higgs sector.

Speaker: Hjalte Frellesvig

danishqft.pdf

09:45 → 10:15 Welcome and coffee

10:15 → 10:45 Four-Fermion Deformations on Line Defects in QED_4 with Yukawas

In this talk we discuss recent developments in Defect Conformal Field Theory (DCFT). Focusing on specific examples in gauge theories, we study how the insertion of a Wilson line (representing an infinitely massive charged source) introduces relevant operators that can trigger a renormalisation group flow on the defect. In particular, we examine how quartic (four-fermion) deformations on the line change the fixed point structure of the theory.

Speaker: Giulia Muco

Danish_QFT_meeting_GiuliaMuco.pdf

10:45 → 11:15 Classifying all Feynman integral geometries for two-loop particle scattering

In this talk, we provide a complete classification of the Feynman integral geometries at two-loop level in four-dimensional Quantum Field Theory. Concretely, we consider a basis of 79 Feynman integrals in the ’t Hooft–Veltman scheme, i.e. with d-dimensional loop momenta and four-dimensional external momenta, and calculate leading singularities for generic values of the masses and momenta. We find that only elliptic curves, hyperelliptic curves of genus 2 and 3 as well as K3 surfaces occur. These geometries determine the space of functions relevant for Quantum Field Theories at two-loop order, including in the Standard Model.

Speaker: Florian Seefeld

Classifying all Feynman integral geometries for two-loop particle scattering.pdf

11:15 → 12:00 Quantum Gravity as a QFT

Quantum gravity remains a fundamental challenge in theoretical physics, with multiple approaches striving for a consistent quantum description of spacetime. Among these, Asymptotically Safe Gravity offers a promising framework based on quantum field theory and on an interacting ultraviolet completion that renders the theory non-perturbatively renormalizable. After reviewing its basics, I will discuss two key questions: how to test its consistency and low-energy implications, and how to compare it with other quantum gravity theories. Both can be tackled by looking at quantum gravity through the lens of effective field theory: mapping different ultraviolet completions onto "landscapes" of effective theories allows for systematic tests against theoretical constraints like positivity bounds, comparisons with other quantum gravity theories—such as the string landscape identified by swampland conjectures—and more direct connections to key questions in black hole physics and cosmology. I will present recent results illustrating these points and their broader implications.

Speaker: Alessia Platania

2025-08 - Danish QFT.pdf

12:00 → 13:00 Lunch break

13:00 → 13:45 QCD under Extreme Conditions – A Lattice View

Understanding the phase structure of Quantum Chromodynamics (QCD) is essential for describing the behaviour of strongly interacting matter at high temperatures and densities, such as those present in the early universe or created in heavy-ion collision experiments. Lattice QCD, which formulates QCD on a discrete spacetime lattice, has become the primary non-perturbative tool for studying the properties of strongly interacting matter from first principles. By enabling controlled numerical simulations, lattice QCD provides crucial theoretical input to complement and guide experimental efforts worldwide.
Despite significant progress, the phase diagram of QCD at nonzero baryon density remains poorly understood, mainly due to the notorious sign problem, which renders standard importance sampling techniques ineffective. The QCD phase diagram, plotted as a function of baryon chemical potential (μ) and temperature (T), is believed to exhibit a rich variety of phases, including a possible critical endpoint and colour-superconducting regions.

Speaker: Benjamin Jaeger

QFT_BJ.pdf

13:45 → 14:15 Gradient flow as a renormalization tool

The Gradient Flow is a smoothing technique that has been extensively studied for its renormalization properties. When combined with the short flow-time expansion, it provides a renormalization scheme in which hadronic matrix elements on the lattice evolve with the flow time, suppressing ultraviolet (UV) divergences. In this scheme, some of the typical lattice challenges—such as operator mixing with lower-dimensional operators—are either avoided or relegated to the perturbative matching stage. I will begin by introducing the Gradient Flow methodology and provide an overview of the short flow-time expansion. I will then present our approach for determining two distinct classes of observables: (1) matrix elements of four-quark operators relevant to neutral meson mixing and meson lifetimes, and (2) renormalized quark masses.

Speaker: Antonio Rago

14:15 → 14:45 The Brief Femtouniverse

No technique used to compute observables, such as the 1/N-expansion or the bootstrap method, is successful for QCD. A method which should work, at least in principle, is a semiclassical van-Vleck formula, applied to the femtouniverse: a small region of Euclidean space-time. This yields a renormalization-group transformation to a lattice model which should be a correct description of the continuum field theory at large distances. To test the method, we apply it to the (well-understood) O(3) nonlinear sigma model in two dimensions.

Speaker: Peter Orland

OrlandDanskQFT25.pdf

14:45 → 15:15 Coffee and departure