Organisers: Nejc Ceplak, Luke Corcoran & Patrick Fritzsch (TCD)
Last Colloquium: 09/04/25 - Uwe-Jens Wiese (University of Bern)
Venue: 4 pm, HMI Seminar Room, Hamilton Building (top floor), Trinity College Dublin
Title: The Importance of Self-Adjointness in Quantum Mechanics.
Abstract: The differences between hermiticity and self-adjointness are rarely emphasized in the teaching of quantum mechanics. However, even simple quantum systems, like a particle in a box, are strongly affected by this issue. I will discuss the most general hard-wall boundary condition that is consistent with unitarity and will investigate its effects on the energy spectrum of a particle in a box. I will then derive a generalized Heisenberg-Robertson-Schroedinger uncertainty relation and construct a self-adjoint momentum operator of a particle confined to a finite volume, whose existence had been questioned for a long time. As a result, the Ehrenfest theorem continues to hold in a finite volume and wave packets bouncing between the walls can be understood in terms of reflecting momenta.
2024/25 Colloquium schedule
2024
Sep 18th: Benoit Vicedo (York)
Sep 25th: Adolfo Holguin (TCD)
Oct 2nd: Alberto Ramos (Valencia)
Oct 9th: Tim Harris (ETH Zürich)
Oct 16th: Dalimil Mazac (Saclay)
Oct 23rd: READING WEEK
Oct 30th: Gui Pimentel (Pisa)
Nov 6th: Sibylle Dreizen (ETH Zürich)
Nov 13th: Carsten Urbach (Bonn)
Nov 20th: Christopher Thomas (Cambridge)
Nov 27th: Anne Spiering (Humboldt Berlin)
2025
Jan 29th: Livia Ferro (Hertfordshire)
Feb 5th: Fernando Romero Lopez (Bern)
Feb 12th: Tudor Dimofte (Edinburgh)
Feb 20th: Samson Shatashvili (TCD), Thursday, 5pm
Feb 26th: Owe Philipsen (Frankfurt)
Mar 5th: READING WEEK
Mar 12th: Sibylle Driezen (ETH Zürich)
Mar 19th: Richard Davison (Heriot-Watt University, Edinburgh)
Mar 26th: Dionysios Anninos (King's College London)
Apr 2nd: Roberto Frezzotti (Rome) [postponed]
Apr 9th: Uwe-Jens Wiese (Bern)
PAST EVENTS:
Colloquium: 26/03/25 - Dionysios Anninos (King's College London)
Venue: 4 pm, HMI Seminar Room, Hamilton Building (top floor), Trinity College Dublin
Title: Partition function of Lambda > 0 Gravity.
Abstract: We discuss Z, the partition function for Lambda > 0 gravity in a variety of contexts. It has been argued that Z captures the quantum entropy of the cosmological horizon. In light of this hypothesis, we consider perturbative and non-perturbative features of Z. Non-perturbative features can stem from contributions of non-spherical Einstein manifolds.
Colloquium: 19/03/25 - Richard Davison (Heriot-Watt University, Edinburgh)
Venue: 4 pm, HMI Seminar Room, Hamilton Building (top floor), Trinity College Dublin
Title: Universal thermalization dynamics in (1+1)d QFTs.
Abstract: Interacting quantum field theories typically thermalize, leading to the emergence of hydrodynamics at late times. I will talk about (1+1)d QFTs at high temperatures, where the proximity to a CFT results in parametrically slow thermalization, with much of the associated dynamics tractable. I will first explain how the UV effective theory – conformal perturbation theory – breaks down at late times giving room for hydrodynamics to emerge. Specialising to the case of large central charge, I will then argue that the IR effective theory – hydrodynamics -- has universal transport coefficients and use this to show that it breaks down at early times due to the existence of thermal CFT excitations. The timescales at which the two effective theories break down agree.
Colloquium:12/03/25 - Sibylle Driezen (ETH Zurich)
Venue: 4 pm, HMI Seminar Room, Hamilton Building (top floor), Trinity College Dublin
Title: On the Integrable Structures in Twist-deformed AdS/CFT.
Abstract: In this talk, I will discuss recent advances in the study of integrable deformations of the AdS₅×S⁵ superstring, focusing on a Homogeneous Yang-Baxter (or Drinfel'd-twist) deformation of the string sigma-model. These deformations extend the familiar framework of (diagonal) TsT transformations and Drinfel’d–Reshetikhin twists into the more intricate non-diagonal and non-abelian settings. I will compare two complementary integrability approaches—one based on the S-matrix and another on the existence of a flat Lax connection—and discuss the (apparent) tension that emerges between them, raising important questions on the nature of integrability in such settings.
Colloquium: 26/02/25 - Owe Philipsen (Goethe University Frankfurt)
Venue: 4 pm, HMI Seminar Room, Hamilton Building (top floor), Trinity College Dublin
Title: Surprises on the way toward the QCD phase diagram.
Abstract: Quantumchromodynamics (QCD) is the fundamental theory of the strong interactions within the Standard Model of Particle Physics. Its phase diagram describes the different forms of hadronic and nuclear matter as a function of temperature and density, and plays an important role in heavy-ion collisions and the physics of the early universe or neutron stars and their mergers. A strong fermion sign problem prohibits numerical simulations of QCD at finite baryon density, so that little knowledge of the phase diagram is available from first principle calculations. I summarise historical expectations and current constraints obtained from simulations using varying parameter values of the underlying theory, and discuss their potential implications for the expected forms of matter.
Colloquium: 20/02/25 - Samson Shatashvili (TCD)
Venue: 5 pm, HMI Seminar Room, Hamilton Building (top floor), Trinity College Dublin (unusual date & time)
Title: Anomalies, Exceptional Holonomy, Supersymmetry and Integrability.
Abstract: I review the results mentioned in the citation of the 2025 Dannie Heineman Prize.
The 2025 Dannie Heineman Prize in Mathematical Physics was awarded to Prof. Shatashvili by the American Physical Society (https://www.aps.org/funding-recognition/prize/dannie-heineman)
"For clever use of various techniques in studying symmetry in quantum field theory, in particular, for work with L. Faddeev on anomalies, with C. Vafa on exceptional holonomy compactifications of superstrings, and for the co-discovery of Bethe/gauge correspondence between supersymmetric vacua and quantum integrability."
Colloquium: 12/02/25 - Tudor Dimofte (Edinburgh)
Venue: 12pm, HMI Seminar Room, Hamilton Building (top floor), Trinity College Dublin
Title: Representing topological line operators
Abstract: Given a quantum field theory, there exist well developed techniques for describing spaces of states, spaces of local operators, and their interactions. But how does one capture the complete set of extended operators in a QFT — and their junctions, collisions, interactions with local operators? In a gauge theory, extended operators (famously) include Wilson lines, but also 't Hooft lines, vortex defects, and potentially much more. I'll describe a conceptual framework for answering this question, inspired by mathematical techniques for representing categories — especially the notions of Tannaka & Koszul duality. Physically, it amounts to probing extended operators with sufficiently nice boundary conditions. I'll then apply the framework in QFT's with some degree of topological invariance, to obtain 1) generalized quantum groups representing all line operators in BPS sectors of 3d N=4 SUSY gauge theories; and 2) new Yangian-like algebras representing line operators in BPS sectors of 3d N=2 gauge theories. In 4d, the same ideas are related to (and inspired by) Costello/Costello-Witten-Yamazaki's realization of Yangians from partially holomorphic Chern-Simons theory.
Colloquium: 05/02/25 - Fernando Romero Lopez (Bern)
Venue: 4pm, HMI Seminar Room, Hamilton Building (top floor), Trinity College Dublin
Title: Hadronic resonances from Lattice QCD
Abstract: The majority of known hadrons in the low-energy QCD spectrum are resonances observed in multi-particle scattering processes. First-principles determinations of the properties of these unstable hadrons are a crucial goal in lattice QCD calculations. Significant progress has been made in developing, implementing and applying theoretical tools that connect finite-volume lattice QCD quantities to scattering amplitudes, enabling determination of masses and widths of various hadronic resonances. In this talk, I will discuss recent advances in lattice QCD studies of meson-baryon resonances, including the Lambda(1405) resonances, as well as three-hadron resonances such as the doubly-charmed tetraquark.
Colloquium: 29/01/25 - Livia Ferro (Hertfordshire)
Venue: 4pm, HMI Seminar Room, Hamilton Building (top floor), Trinity College Dublin
Title: The Geometry behind Scattering Amplitudes
Abstract: In recent years it has become clear that particular geometric structures, called positive geometries, underlie various observables in quantum field theories. In this talk I will review this connection for scattering amplitudes. After a broad introduction and review of the main ingredients involved, I will focus on maximally supersymmetric Yang-Mills theory and discuss a positive geometry encoding scattering processes in this theory -- the momentum amplituhedron. Finally, I will present some of the main goals and research directions for the future.
Colloquium: 27/11/24 - Anne Spiering (Humboldt University, Berlin)
Venue: 4pm, HMI Seminar Room, Hamilton Building (top floor), Trinity College Dublin
Title: Two-loop scattering in planar N=4 SYM theory
Abstract: The pentabox and double-pentagon Feynman integrals, together with the double box, take on a central role in planar N=4 SYM theory as they form a basis for two-loop scattering in this theory. Their direct integration is challenging due to the presence of several elliptic curves. After a brief review of the one-loop case, I will present recent progress on the two-loop integrals, discussing their relation to higher-dimensional one-loop integrals and their symbol structure.
Colloquium: 20/11/24 - Christopher Thomas (University of Cambridge, UK)
Venue: 4pm, HMI Seminar Room, Hamilton Building (top floor), Trinity College Dublin
Title: Hadron scattering, resonances and exotics from Lattice QCD
Abstract: The spectroscopy and interactions of hadrons probe thestrongly-interacting regime of QCD, and in recent years experiments haveobserved a number of puzzling hadrons that challenge our understandingof the strong interaction. Lattice QCD provides a method for performingfirst-principles computations of the properties of hadrons and hence aQCD-based understanding of the phenomena. However, the majority ofhadrons decay strongly, i.e. they are resonances, and latticecalculations of these are challenging. I will discuss recent progressand a selection of work that has advanced our understanding of hadrons,including results relevant for some exotic charm mesons.
Colloquium: 13/11/24 - Carsten Urbach (University of Bonn)
Venue: 4pm, HMI Seminar Room, Hamilton Building (top floor), Trinity College Dublin
Title: The omega-meson from Lattice QCD
Abstract: The omega-meson is one of the prominent resonances in QCD decaying into three particles in the final state. We will discuss how to investigate three particle resonances in Euclidean lattice field theories and present a first study of the omega-meson from lattice QCD.
Colloquium: 30/10/24 - Guilherme L. Pimentel (Pisa, Scuola Normale Superiore)
Venue: 4pm, HMI Seminar Room, Hamilton Building (top floor), Trinity College Dublin
Title: Kinematic flow and the emergence of time
Abstract: I will start with a broad overview of the theory of initial conditions of the universe, what we know and what we hope to know in the near future.
Then I will describe some recent work. Motivated by precision calculations in primordial cosmology, a bootstrap approach has been developed over the past few years. A central element in this approach is to determine static differential equations in terms of boundary momenta (at the reheating surface), instead of performing time-evolution integrals. While investigating a toy model of cosmology to better understand these differential equations, we found an autonomous structure, from which time evolution seems to be an output. I will describe the rules of this “kinematic flow,” and mention some work in progress to further develop it.
Colloquium: 16/10/24 - Dalimil Mazac (IPhT Saclay)
Venue: 4pm, HMI Seminar Room, Hamilton Building (top floor), Trinity College Dublin
Title: Conformal field theories, hyperbolic manifolds, and L-functions
Abstract: Recently, the conformal bootstrap was adapted to produce rigorous and strikingly powerful bounds on the spectra of hyperbolic manifolds. Under the analogy between CFTs and hyperbolic manifolds, scaling dimensions become eigenvalues of the Laplacian, and OPE coefficients turn into integrals of triple products of eigenfunctions. The latter are in turn related to L-functions. I will review these developments and explain what they teach us about conformal field theory.
Colloquium: 09/10/24 - Tim Harris (ETH Zuerich)
Venue: 4pm, HMI Seminar Room, Hamilton Building (top floor), Trinity College Dublin
Title: QCD at high temperature: theory and phenomenology from the lattice
Abstract: In this talk I will discuss a few features of QCD at high temperatures where chiral symmetry is restored but interactions are not necessarily weak. The introduction of the scale of temperature allows an effective description whose applicability can be tested definitively using lattice field theory for certain classes of observables, such as the screening lengths defined by spatial correlators. These screening lengths also govern the behaviour of Euclidean correlators at large separations, which have phenomenological relevance to heavy-ion collisions. In particular, the correlator of the electromagnetic current can be related to the structure functions which parameterize the scattering of an energetic lepton off the medium. On the other hand, for lightlike kinematics it determines the production of real photons. Recent numerical studies have shown lattice computations can constrain the thermal emissivity, which could have an impact in explaining the so-called direct photon puzzle -- an excess in the yield of thermal photons observed at experiments at RHIC and the LHC over model predictions.
Colloquium: 02/10/24 - Alberto Ramos (IFIC, Valencia)
Venue: 4pm, HMI Seminar Room, Hamilton Building (top floor), Trinity College Dublin
Title: The strong coupling as a fundamental parameter of the standard model
Abstract: The strong coupling is one of the fundamental parameters of the standard model. However due to the strongly coupled nature of QCD it is difficult to disentangle its intrinsic value from the process used to extract its value. Although some determinations of the strong coupling based on lattice QCD suffer from a similar problem, in this talk I will argue that some new developments in lattice QCD allow to shed some light in this problem.
Colloquium: 25/09/24 - Adolfo Holguin (TCD)
Venue: 4pm, HMI Seminar Room, Hamilton Building (top floor), Trinity College Dublin
Title: Large BPS operators, determinant modifications, and emergent Yang-Mills
Exercises01-Solutions.pdf Abstract: Recently there has been renewed interest in the large N limit of operators whose charges scale with N in gauge theories. For theories with dual string descriptions, this is related to various non-perturbative stringy effects such as D-branes and bulk topology change. One of the main obstacles for studying this regime of holographic gauge theories is the breakdown of the planar expansion in the large N limit. I will explain an approach to this problem for certain BPS sectors in N=4 SYM and their near-BPS limits. As a concrete application I will demonstrate how the large N limit of certain near-BPS modifications of determinant operators precisely map to super Yang-Mills modes on the world volume of a brane in the dual gravity description. If time permits I will describe some progress in understanding three point correlation functions of supersymmetric heavy operators.
Colloquium: 18/09/24 - Benoit Vicedo (York)
Venue: 4pm, HMI Seminar Room, Hamilton Building (top floor), Trinity College Dublin
Title: (Higher) gauge theory and (higher dimensional) integrable field theories
Abstract: A novel approach for understanding integrable systems based on gauge theory was proposed five years ago by Costello, Witten and Yamazaki. The general idea is to include the so-called spectral parameter of the Lax formulation of a given integrable system as part of the spacetime of a higher dimensional gauge theory. I will begin by reviewing this story in the case of finite-dimensional integrable system (or 0+1-dimensional integrable field theories), for which the relevant gauge theory is 3-dimensional semi-holomorphic BF theory, and also in the case of 1+1-dimensional integrable field theories, for which the relevant gauge theory is 4-dimensional semi-holomorphic Chern-Simons theory. I will then describe a way of extending these ideas to describe 2+1-dimensional integrable field theories using a certain higher gauge theory called 5-dimensional semi-holomorphic 2-Chern-Simons theory.