Dynamics in Classical Gravity from Scattering Amplitudes

• Emil Bjerrum-Bohr

Room: U220

3-body systems in strong-gravity

• Marta Orselli

Room: U220 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.

Kerr Black Hole Dynamics from an Extended Polyakov Action

• Gang Chen

Room: U220 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.

Perturbative Computations from Curved Spacetimes

• Nabha Shah

Room: U220 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.

Perturbative TQFTs

• Konstantin Wernli

Room: U220 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.

Resurgence in Topological Quantum Field Theory

• William Mistegård

Room: U220 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.

A BPS Road to Holography: Decoupling Limits and Non-Lorentzian Geometries

• Niels Obers

Room: U220 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.

Boundary energy-momentum tensor for asymptotically flat spacetimes

• Emil Have

Room: U220 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.

Integrable corners in the space of Gukov-Witten defects

• Adam Chalabi

Room: U220 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.

Amplitudes, intersection theory, and Higgs physics

• Hjalte Frellesvig

Room: U220 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.

Four-Fermion Deformations on Line Defects in QED_4 with Yukawas

• Giulia Muco

Room: U220 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.

Classifying all Feynman integral geometries for two-loop particle scattering

• Florian Seefeld

Room: U220 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.

Quantum Gravity as a QFT

• Alessia Platania

Room: U220 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.

QCD under Extreme Conditions – A Lattice View

• Benjamin Jaeger

Room: U220 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.

Gradient flow as a renormalization tool

• Antonio Rago

Room: U220 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.

The Brief Femtouniverse

• Peter Orland

Room: U220 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.