Dublin Area Theoretical Physics Colloquium 2023/24

Colloquium: 27/03/24 - Michal Heller (Ghent)

Venue: 4pm, Salmon Lecture Theatre, Hamilton Building (ground floor), Trinity College Dublin

Title: Gravity and Quantum Fields through Quantum Physics Lenses

Abstract:  In the XXI century a new web of connections between different branches of physics was discovered. It entails deep relations between gravity and quantum field theory on one side and quantum information processing and quantum many-body physics on the other. In my colloquium I will discuss how progress along these lines is affecting our understanding of gravity in black hole and cosmological spacetimes. I will also elucidate novel quantum field theory problems it is raising, such as questions about properties of entanglement or hardness of state preparation using limited resources (complexity).

Colloquium: 20/03/24 - Mark Mezei (Oxford)

Venue: 4pm, Salmon Lecture Theatre, Hamilton Building (ground floor), Trinity College Dublin

Title: Quantum chaos and gravity

Abstract:  Chaos underlies the thermal behaviour in quantum systems. Black holes are thermal objects. In recent years a connection between chaos in ordinary quantum systems and the dynamics of black holes has been established. In this talk, I discuss what this connection teaches us about the dynamics of entanglement in many-body quantum systems and about the interior of old black holes.

Colloquium: 13/03/24 - Dmitry Noshchenko (DIAS)

Venue: 4pm, Salmon Lecture Theatre, Hamilton Building (ground floor), Trinity College Dublin

Title: Topology, physics, and hidden mathematics of knots and 3-manifolds

Abstract:  This talk is a review of the (old and new) interfaces between low-dimensional topology, quantum field theory, and homological algebra.

 Colloquium: 28/02/24 - Nikolai Husung (IFT, Universidad Autónoma de Madrid)

Venue: 4pm, Salmon Lecture Theatre, Hamilton Building (ground floor), Trinity College Dublin

Title: Lattice QCD and the aim for precision physics

Abstract:  To pin down new physics in BSM searches we need a precise knowledge of the physics within the Standard Model. Lattice QCD is able to provide non-perturbative first-principle predictions for the strong interaction such as the mass spectrum for hadrons, decay constants etc. Uncertainties in any of these predictions directly impact bounds on new physics and must be kept under control. I will give a brief introduction to the ideas behind lattice QCD and try to highlight particular sources of systematic errors before focusing on the continuum extrapolation as one of the central steps to extract continuum physics.

Colloquium: 21/02/24 - Elli Pomoni (DESY)

Venue: 4pm, Salmon Lecture Theatre, Hamilton Building (ground floor), Trinity College Dublin

Title: Exploring Thermal CFTs

Colloquium: 14/02/24 - Eric Bergshoeff (Groningen)

Venue: 4pm, Salmon Lecture Theatre, Hamilton Building (ground floor), Trinity College Dublin

Title: The Comeback of Carroll

Abstract:  Carroll symmetries were introduced many years ago by Levy-Leblond and Gupta as a possible contraction of the Lorentz symmetries in which effectively the speed of light is sent to zero. The name was inspired by the bizarre property that Carroll particles cannot move. After many years of silence Carroll symmetries have returned to the stage since they have been recognized as symmetries that do occur in several special situations such as the horizon of a black hole. In this presentation I will discuss some of the basic properties and mysteries of Carroll symmetries.

Colloquium: 07/02/24 - Jelle Hartong (Edinburgh)

Venue: 4pm, Salmon Lecture Theatre, Hamilton Building (ground floor), Trinity College Dublin

Title: Non-Lorentzian String Theories

Abstract: I will give an introduction to various non-Lorentzian string theories that have been studied in recent years. This includes generalisations of the Gomis—Ooguri string (both open and closed) and non-relativistic strings that arise for example via near-BPS limits of the AdS/CFT correspondence (known as spin matrix theory). The latter are an interesting novel class of closed strings whose worldsheet theory is described by a non-relativistic sigma model.

Colloquium: 31/01/24 - Simon Kuberski (CERN)

Venue: 4pm, Salmon Lecture Theatre, Hamilton Building (ground floor), Trinity College Dublin

Title: Hadronic contributions to the anomalous magnetic moment of the muon and lattice QCD

Abstract: The anomalous magnetic moment of the muon is considered to be an excellent probe for new physics beyond the Standard Model of particle physics. It can be determined with high precision, both experimentally and theoretically, revealing a long-standing tension between the Standard Model prediction and Nature. Recent and upcoming reductions of the experimental uncertainties by the Muon g-2 experiment at Fermilab call for a similar progress for the theory calculation.

The uncertainty in the Standard Model prediction is currently dominated by hadronic contributions, which are computed in the theory of strong interactions, Quantum Chromodynamics (QCD). Traditionally, these contributions have been determined using data-driven methods, with their precision limited by tensions in the experimental input data. Lattice QCD has emerged as a framework to calculate these hadronic contributions with precision from first principles. I will review the current status of lattice QCD calculations and the major sources of uncertainty that must be addressed to achieve the precision targets set by experimental successes.

Colloquium: 29/11/23 - Ana-Maria Raclariu (UvA)

Venue: 4pm, Salmon Lecture Theatre, Hamilton Building (ground floor), Trinity College Dublin

Title: Entanglement, soft modes and celestial CFT

Abstract: Over the past decade a rich symmetry structure was uncovered in the infrared sector of gauge and gravity theories in asymptotically flat spacetimes. I will revisit the calculation of entanglement entropy in free Maxwell theory in 4-dimensional Minkowski space in the light of these developments. Weyl invariance allows for this theory to be embedded inside the Einstein static universe. Future null infinity can be regarded as the union of Cauchy slices inside the future Milne patches of two Minkowski geometries related by a conformal inversion. I will describe the soft sectors of the two patches and the associated constraints. I will show that conformally soft mode configurations at the entangling surface, or equivalently, correlated fluctuations in the large gauge charges of the two Milne patches, give a non-trivial contribution to the entanglement entropy across a cut of future null infinity. I will conclude with some comments on the implications for holography in flat space.

Colloquium: 22/11/23 - Rainer Sommer (DESY Zeuthen)

Venue: 4pm, Salmon Lecture Theatre, Hamilton Building (ground floor), Trinity College Dublin

Title: Effective Field Theories and Challenges in Lattice QCD

Abstract: Decays of B-mesons are rare and therefore new interactions may become visible beneath the Standard Model processes once experiment and theory are precise enough. Because the b-quark mass is significantly above the typical QCD scale, accurate lattice computations require enormous resources. We show how a simple and transparent non-perturbative use of effective field theory can meet this challenge.
Also for the determination of the strong coupling a large scale ratio is required. Here only a high energy scale enables the application of perturbation theory with confidence and precision. Surprisingly also here effective field theories help to overcome the challenge.

Colloquium: 15/11/23 - Carlo Heissenberg (Queen Mary)

Venue: 4pm, Salmon Lecture Theatre, Hamilton Building (ground floor), Trinity College Dublin

Title: Dynamics of black-hole encounters and gravitational waves from the eikonal operator

Abstract: The eikonal exponentiation provides a flexible tool to extract the classical limit of scattering amplitudes and to obtain predictions for classical gravitational observables that characterize collisions of compact objects. Being organized as a series expansion in powers of the gravitational coupling, Newton's constant, amplitude methods naturally apply to the post-Minkowskian regime, in which gravitational interactions are weak, while velocities are not necessarily small compared to the speed of light. In this talk, I will discuss how the elastic eikonal phase dictates the deflection experienced by each object during a two-body encounter, and how this phase can be promoted to an operator in order to account for gravitational-wave emissions, calculating also dissipative observables associated to the gravitational field itself produced during the encounter. As an application, I will focus on the total angular momentum that a binary system loses to the gravitational field, showing how it can be calculated from the eikonal operator, including the cases of tidally deformable and of spinning compact objects.

Colloquium: 08/11/23 - Gurtej Kanwar (University of Bern)

Venue: 4pm, Salmon Lecture Theatre, Hamilton Building (ground floor), Trinity College Dublin

Title: Machine learning for lattice field theory

Abstract: Lattice field theory provides a non-perturbative approach to understanding strongly interacting field theories, such as the quantum chromodynamics (QCD) sector of the Standard Model. Among other applications, lattice QCD calculations will be crucial in the effort to pin down whether observed experimental tensions, e.g. in the muon g-2, are evidence of new physics beyond the Standard Model. State-of-the-art lattice calculations are however limited by the large computational cost required to perform Monte Carlo integration with controlled statistical noise. I will discuss recent progress in applying machine learning in order to improve efficiency in these calculations without compromising exactness.

Colloquium: 01/11/23 - Cyril Closset (University of Birmingham)

Venue: 4pm, Salmon Lecture Theatre, Hamilton Building (ground floor), Trinity College Dublin

Title: Global structures of SQFTs from rank-one Seiberg-Witten geometries

Abstract: I will explore subtle aspects of rank-one 4d N=2 supersymmetric QFTs through their low-energy Coulomb-branch physics. This low-energy Lagrangian is famously encoded in the Seiberg-Witten (SW) curve, which is a one-parameter family of elliptic curves. Less widely appreciated is the fact that various properties of the QFTs, including properties that cannot be read off from the Lagrangian, are nonetheless encoded into the SW curve, in particular in its Mordell-Weil group. This includes the global form of the flavour group, the one-form symmetries under which defect lines are charged, and the "global form" of the theory. In particular, I will discuss in detail the difference between the pure SU(2) and the pure SO(3) N=2 SYM theories from this perspective. I will also comment on 5d SCFTs compactified on a circle in this context.

Colloquium: 18/10/23 - Daniel G. Figueroa (IFIC, CSIC - Valencia University, Valencia, Spain)

Venue: 4pm, Salmon Lecture Theatre, Hamilton Building (ground floor), Trinity College Dublin (connected via zoom)

Title: Probing the early Universe with gravitational wave backgrounds

Abstract: We will review both theoretical and observational aspects of gravitational wave backgrounds of cosmological origin. We will present a classification of backgrounds and a quantification of our ability to use them as a probe of early Universe phenomena, opening a new observational window to energy scales way above the reach of any terrestrial means. Our discussion will include the latest results from Pulsar Timing Array collaborations (e.g. nanoGrav), which have recently announced the first evidence on the existence of a background of gravitational waves. This talk will be given in a colloquium style, making it accessible to a wide audience of physicists. 

Colloquium: 11/10/23 - Ömer Gurdogan (University of Southampton)

Venue: 4pm, Salmon Lecture Theatre, Hamilton Building (ground floor), Trinity College Dublin

Title: Antipodal dualities: reading form factors backwards

Abstract: Our understanding of scattering amplitudes is in a process of perpetual refinement where new results lead to new insights, which in turn enable even more ambitious calculations. I will report on a recent observation that certain amplitudes and form factors are mapped to each other under the antipode of the Hopf algebra of multiple polylogarithms. This observation is based on an eight-loop calculation of form factors, which turn out to be very amenable to the symbol bootstrap approach.

Colloquium: 04/10/23 - Maxwell T. Hansen (University of Edinburgh)

Venue: 4pm, Salmon Lecture Theatre, Hamilton Building (ground floor), Trinity College Dublin

Title: Multi-particle observables from a finite Euclidean spacetime

Abstract: Numerical calculations of lattice regularized QFTs are a powerful tool to understand such theories when analytic methods are not applicable. However, the utility of numerical results can be affected by two issues: (i) calculations are necessarily performed in a finite-volume spacetime and (ii) imaginary-time correlation functions are evaluated. Both aspects play an especially important role for multi-particle observables including scattering and decay amplitudes and inclusive rates. In this colloquium, I will discuss progress for extracting such observables from numerical lattice field theory based on two strategies. One is to use the finite-volume as a tool, rather than an unwanted artefact, and to apply generic field theoretic relations between finite-volume quantities and infinite-volume amplitudes. The second is to carefully regulate the inverse Laplace transform, in order to estimate physical observables directly from numerical correlators.

Colloquium: 27/09/23 - Rob Klabbers (Humboldt University Berlin)

Venue: 4pm, Salmon Lecture Theatre, Hamilton Building (ground floor), Trinity College Dublin

Title: The deformed Inosemtsev spin chain

Abstract: The ubiquitous Heisenberg xxx spin chain admits many deformations, for example the xxz and xyz spin chains, which have deformed spin interactions compared to xxx. The Inozemtsev spin chain is another deformation of xxx: one can interpret it as a deformation of the potential controlling the strength of interactions, causing it to have interactions between all pairs of spins. Its deformation parameter controls the effective interaction distance, going from the nearest-neighbour xxx chain to the truly long-range and integrable Haldane-Shastry spin chain.

I will present the construction of a deformation of the Inozemtsev spin chain that interpolates between a Heisenberg xxz spin chain and the long-range q-deformed Haldane-Shastry model, presenting an answer to a long-standing question. This deformation is integrable by virtue of its connection via freezing to a novel elliptic dynamical spin-Ruijsenaars model. I will discuss its properties and show how it encompasses several interesting new models, including a dynamical xxz chain, reachable by various limits.