2nd Annual Workshop on Self-Force and Amplitudes

9 Sept 2025, 09:15 → 12 Sept 2025, 23:00 Europe/London

Room 1077 (Building 6)

Adam Pound (University of Southampton), Chris Kavanagh (University College Dublin), Jan Plefka, Riccardo Gonzo (University of Edinburgh), Zachary Nasipak (University of Southampton)

The 2nd Annual Workshop on Self-Force and Amplitudes will be hosted by the STAG Research Centre at the University of Southampton from 9th - 12th September 2025. 

Recent developments in perturbative quantum field theory have offered new insights into the classical two-body dynamics in the post-Minkowskian expansion (i.e., expansion in Newton's constant), leveraging efficient computational techniques traditionally used for collider physics. At the same time, the gravitational self-force expansion has allowed the gravitational-wave community to develop a description of the two-body dynamics which is fully non-perturbative in the coupling, while being accurate only in the limit of small mass ratios.

There are exciting prospects in uniting these two complementary approaches, possibly yielding powerful new modeling methods for gravitational-wave astronomy and new insights into the connections between gravity and quantum field theory. There have recently been notable steps toward this goal, but much more remains to be done to fully benefit from synergies between the two methods. This workshop is a sequel to the event held at the Higgs Centre in Edinburgh in 2024, which brought together experts from both communities to establish new collaborations. Topics will include

• using data from scattering scenarios to inform models of gravitationally bound systems
• using the self-force expansion to determine unknown high-order terms in the post-Minkowskian series, and vice versa
• using self-force results to inform resummations of post-Minkowskian calculations, and vice versa
• validating and informing resummation techniques using numerical relativity simulations of scattering orbits
• describing Kerr black holes with amplitudes and point particles
• investigating double copy structures in classical gravity and black hole perturbation theory

 

Due to limited space, registration will be moderated. Preference will be given to participants who also wish to attend the workshop on Nonlinear Black Hole Perturbation Theory, which will be held 15-17 September at the University of Nottingham. The deadline to register was 1 August 2025.

Invited speakers

• Leor Barack
• Poul Daamgard
• Thibault Damour
• Gustav Jakobsen
• Dimitrios Kosmopoulos
• Oliver Long
• Gustav Mogull
• Julio Parra-Martinez
• Radu Roiban
• Nabha Shah
• Canxin Shi
• Davide Usseglio
• Maarten van de Meent
• Pierre Vanhove
• Chris Whittall
• Mao Zeng

 

Funding Sources

This workshop is funded by the UKRI/ERC grant GWModels, the ERC grant GraWFTy, and the STAG Research Centre.

Tuesday 9 September

09:15 → 09:30 Welcome

09:30 → 10:30 A view of binary dynamics from infinity

Quantum field theory and scattering are attractive and powerful probes of gravitational interactions. In this talk we survey the current status of scattering-based calculations for the gravitational two-body problem, their application to the bound regime and their synergy with the (gravitational) self-force.

Speaker: Radu Roiban

Roiban_Southhampton.pdf

10:30 → 11:10 coffee break

11:10 → 12:10 High Precision Gravitational Scattering: PM, MPM, SF, EFT, EOB, TF, NR and All That

The synergies between various approaches to the 2-body problem will be reviewed, as well as the role of the EOB formalism in concretizing these synergies. High-post-Newtonian-order connections between Tutti Frutti and Worldline EFT will be discussed.

Speaker: Thibault Damour

12:10 → 13:30 lunch

13:30 → 14:30 From Black Hole Scattering to Gravitational Waveforms

In this talk I will outline a full workflow from classical black hole scattering to producing gravitational waveforms in bound binary systems. This will include our recent computation of 5PM-1SF scattering observables using the Worldline Quantum Field Theory (WQFT) formalism, Effective-One-Body (EOB) resummation and comparisons with NR data both for scattering and bound orbits.

Speaker: Gustav Mogull

southampton25.pdf

14:30 → 15:10 coffee

15:10 → 16:10 Discussion

Speaker: Maarten van de Meent

mvdm_SFandA.pdf

16:10 → 16:40 Quantum spectral method

Speaker: Ofri Telem (The Hebrew University of Jerusalem)

Southampton- Bound-Unbound Universality and the All-Order Semi-Classical Wave Function in Schwarzschild.pdf

17:00 → 18:30 Reception with drinks & canapes

Wednesday 10 September

09:30 → 10:00 Numerical approaches to self-force calculations along scatter orbits

In this talk we will review the methods used to perform numerical calculations of the self-force along scatter geodesics in black hole spacetimes. Starting with a general introduction to the calculation of the self-force by mode-sum regularisation, we will move on to discuss two extant numerical platforms for calculating the scalar-field self-force along scatter geodesics, one of which solves the field equation in the time-domain [Phys. Rev. D 106, 104031] and the other in the frequency-domain [Phys. Rev. D 108, 064017]. We will only highlight the basic merits and limitations of each approach here; for details of the numerical results obtained using these codes, see the following talk by O. Long. We then summarise some new approaches currently under development, including a detailed look at a novel method that uses the Gegenbauer reconstruction technique to resolve some shortcomings of the existing frequency-domain approach. We conclude by discussing the outlook for extending numerical scalar field calculations to the full gravitational self-force problem.

Speaker: Chris Whittall

Chris Whittall 2nd SF meets Amplitudes.pdf

10:00 → 10:30 Applications of numerical self-force scattering simulations

Following the discussion of how to calculate the self-force on scattering orbits, I will discuss the applications of the results of these simulations. This starts with results from scalar self-force scattering, including radiated and absorbed fluxes, a resummation of post-Minkowskian that improves the faithfulness to the numerical results across the whole parameter space, and the use of scalar self-force information to perform self-consistent evolution in Numerical Relativity. I will continue by discussing the steps required to perform the first calculations of the gravitational self-force on a scattering orbit and present new results of the gravitational self-force radiated and absorbed fluxes.

Speaker: Oliver Long

SF Amp 25 Olly.pdf

10:30 → 11:10 coffee break

11:10 → 12:10 Updates on Black Hole Scattering from Self Force

In this talk I will discuss the general strategy employed for solving analytically the Teukolsky equation where the perturbation is sourced by a particle in a hyperbolic orbit. This method relies on a combination of post-Newtonian (PN) and post-Minkowskian (PM) expansion in order to extract analytical information and it has been used for studying the scattering of a scalar charge around a Schwarzschild black hole. In the second part of my talk I’ll discuss the state of our works in the gravitational case, highlighting the difficulties faced in going to high order in PM and PN for the computation of the waveform and the fluxes.

Speaker: Davide Usseglio

12:10 → 13:30 lunch

13:30 → 14:30 Extracting spinning two-body observables from S-matrix

I will present a novel method for extracting observables for two-body scattering systems from a set of generating functions, with full spin dependence. The approach uses the classical limit of the logarithm of the quantum S-matrix as generating functions. The 4-point matrix element of Log(S) gives the radial action, corresponding to conservative effects, whereas the higher-point contributions encode radiative information. The observables, such as momentum impulse, orbital angular momentum, and waveform, are obtained by applying differential operators, which are constructed from Dirac brackets and the generating functions, to the initial value of the observable. We demonstrate its power by calculating new high-precision results, including the impulse and spin kick for a probe in Kerr up to $O(G^6 s^4)$, and the change in angular momentum for generic masses up to $O(G^2 s^11)$. Via analytic continuation, we can also provide information about bound orbits, such as their fundamental frequencies.

Speaker: Canxin Shi

extracting observables_Southampton.pdf

14:30 → 15:10 coffee break

15:10 → 16:10 Discussion

Speaker: Leor Barack

Thursday 11 September

09:30 → 10:30 Methods for computing observables in classical gravity

In this talk we will present various methods that have been developed recently for computing observables in classical gravity.

Speaker: Pierre Vanhove

seminar-selfforceamplitde-Southampton-septembre-2025.pdf

10:30 → 11:10 coffee break

11:10 → 12:10 Self-force and Loops in Black Hole Scattering

I present recent progress on the classical loop (post-Minkowskian)
expansion of black-hole scattering and its relation to the self-force
expansion. I will focus on how these expansions are organized within
worldline quantum field theory and its diagrammatic framework. This
includes our novel four-loop results, higher-spin observables, and open
puzzles that point to future work.

Speaker: Gustav Jakobsen

southampton.pdf

12:10 → 13:30 lunch

13:30 → 14:30 Solving the Einstein equations by quantum field theory methods

Inspired by the perturbiner method of quantum field theory I describe how to rephrase the perturbative solution of the Einstein equations in terms of an iterative scheme. As an application, I outline how to compute the metric outside a localized region of stationary matter to arbitrarily high order in the coupling G.

Speaker: Poul Damgaard

14:30 → 15:10 coffee break

15:10 → 16:10 Discussion

Speaker: Mao Zeng

19:00 → 22:30 Conference dinner at Bacaro Southampton

https://www.bacarosouthampton.com/

Friday 12 September

09:30 → 10:30 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

NabhaShah_2ndSFandAmp.pdf

10:30 → 11:10 coffee break

11:10 → 12:10 Love Numbers and Self Force from Effective Field Theory

I will introduce a new formalism that combines techniques from Effective Field Theory (EFT) with solutions to Black Hole Perturbation Theory. I will present new results obtained with this formalism for dynamical EFT Love numbers and discuss prospects for the computation of Self-Force observables.

Speaker: Dimitrios Kosmopoulos

12:10 → 13:10 Discussion

Speaker: Julio Parra-Martinez