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Seminars at

Found at least 20 result(s)

28.05.2024 (Tuesday)

Generalized symmetries and duality in lattice models using tensor networks

Exceptional Seminar Laurens Lootens (Cambridge)

at:
15:00 QMUL
room G.O. Jones 208
abstract:

In recent years, there has been a lot of interest in a generalized notion of symmetry, obtained by relaxing the invertibility constraint and/or allowing symmetry operators to act on submanifolds rather than the full space. The mathematical structure underlying these generalized symmetries is provided by (higher) category theory, but it turns out that in the lattice setting, the abstract categorical formulation can be broken down to concrete tensor network operators that realize these generalized symmetries. In a certain sense, these tensor network operators provide the lattice representation theory of these generalized symmetries. As an application, I will explain how this representation theory provides a systematic, constructive theory for duality transformations on the lattice. Additionally, I will explain how dualities and generalized symmetries can be turned into unitary operators by including an ancillary degree of freedom, turning them into completely positive maps.

23.05.2024 (Thursday)

Tracy-Widom distribution in supersymmetric gauge theories

Regular Seminar Gregory Korchemsky (IPhT Saclay)

at:
14:00 QMUL
room G.O. Jones 208 and Zoom
abstract:

It has recently been recognized that various observables in different four-dimensional supersymmetric gauge theories can be computed for an arbitrary 't Hooft coupling as determinants of certain semi-infinite matrices. It turns out that these quantities can be expressed as Fredholm determinants of the so-called Bessel kernel and they are closely related to celebrated Tracy-Widom distribution (more precisely, its finite temperature generalization) describing level-spacing distributions in matrix models. We exploit this relation to determine their dependence on the ’t Hooft coupling constant. Unlike the weak coupling expansion, which has a finite radius of convergence, the strong coupling expansion is factorially divergent, necessitating the inclusion of nonperturbative, exponentially small corrections. We develop a method to systematically compute these corrections and discuss the resurgent properties of the resulting transseries.

03.05.2024 (Friday)

Classical Black Hole Scattering from a World-Line Quantum Field Theory

Exceptional Seminar Jan Plefka (Humboldt U.)

at:
15:00 QMUL
room G.O Jones 610 and Zoom
abstract:

Predicting the outcome of scattering processes of elementary particles in colliders is the central achievement of relativistic quantum field theory applied to the fundamental (non-gravitational) interactions of nature. While the gravitational interactions are too minuscule to be observed in the microcosm, they dominate the interactions at large scales. As such the inspiral and merger of black holes and neutron stars in our universe are now routinely observed by gravitational wave detectors. The need for high precision theory predictions of the emitted gravitational waveforms has opened a new window for the application of perturbative quantum field theory techniques to the domain of gravity. In this talk I will show how observables in the classical scattering of black holes and neutron stars can be efficiently computed in a perturbative expansion using a world-line quantum field theory; thereby combining state-of-the-art Feynman integration technology with perturbative quantum gravity. Here, the black holes or neutron stars are modelled as point particles in an effective field theory sense. Fascinatingly, the intrinsic spin of the black holes may be captured by a supersymmetric extension of the world-line theory, enabling the computation of the far field wave-form including spin and tidal effects to highest precision. I will review our most recent results at the fifth order in the post-Minkowskian expansion amounting to the computations of tens of thousands of four loop Feynman integrals.

30.04.2024 (Tuesday)

Conformal geometry from entanglement

Exceptional Seminar Bowen Shi (UCSD)

at:
15:00 QMUL
room GO Jones 610
abstract:

In a physical system with conformal symmetry, observables depend on cross-ratios, measures of distance invariant under global conformal transformations (conformal geometry for short). We identify a quantum information-theoretic mechanism by which the conformal geometry emerges at the gapless edge of a 2+1D quantum many-body system with a bulk energy gap. We introduce a novel pair of information-theoretic quantities (c,n) that can be defined locally on the edge from the wavefunction of the many-body system, without prior knowledge of any distance measure. We posit that, for a topological groundstate, the quantity c is stationary under arbitrary variations of the quantum state, and study the logical consequences. We show that stationarity, modulo an entanglement-based assumption about the bulk, implies (i) c is a non-negative constant that can be interpreted as the total central charge of the edge theory. (ii) n is a cross-ratio, obeying the full set of mathematical consistency rules, which further indicates the existence of a distance measure of the edge with global conformal invariance. Thus, the conformal geometry emerges from a simple assumption on groundstate entanglement. The stationarity of c is equivalent to a vector fixed-point equation involving n, making our assumption locally checkable. If time permits, we discuss a class of modular flow on a disk, which creates only edge excitations. We intuitively explain why Virasoro algebra can be revealed from a single wavefunction by analyzing such modular flows.

26.04.2024 (Friday)

Non-invertible symmetries for qubits

Exceptional Seminar Shu-Heng Shao (Stony Brook)

at:
11:30 QMUL
room G. O. Jones 610
abstract:

I'll discuss the exact non-invertible Kramers-Wannier symmetry of 1+1d lattice models on a tensor product Hilbert space of qubits. This symmetry mixes with lattice translations, and obeys a different algebra compared to the continuum one. The non-invertible symmetry leads to a constraint similar to that of Lieb-Schultz-Mattis, implying that the system cannot have a unique gapped ground state. It is either in a gapless phase or in a gapped phase with three (or a multiple of three) ground states, associated with the spontaneous breaking of the non-invertible symmetry.

25.04.2024 (Thursday)

From Correlators to massive amplitudes in N = 4 SYM

Regular Seminar Frank Coronado (ETH Zurich)

at:
14:00 QMUL
room G. O. Jones 610 and Zoom
abstract:

In planar N=4 SYM, massless scattering amplitudes are dual to null polygonal Wilson loops (T-duality) or the same as the four-dimensional null limit of stress-tensor correlators. I will present a (conjectured) generalization of this duality which equates correlators of determinant operators, in a special ten-dimensional null limit, with massive scattering amplitudes in the Coulomb branch of N=4. This determinant operator is a generating function of all half-BPS single-traces operators. By taming it on twistor space I will show its correlators have ten dimensional poles which combine 4d space-time and 6d R-charge kinematics.

24.04.2024 (Wednesday)

Holography in the Gravitational Wave Era

Exceptional Seminar David Mateos (ICC Universitat de Barcelona and ICREA)

at:
12:00 QMUL
room GO Jones 610
abstract:

The discovery of gravitational waves has opened a new experimental window into the Universe. The fact that the relevant dynamics is often out of equilibrium offers a golden opportunity for holography to make a unique impact on cosmology and astrophysics. I will illustrate this with applications to cosmological phase transitions, to neutron star mergers and to the BKL dynamics near a cosmological singularity.

19.04.2024 (Friday)

Bootstrapping N = 4 sYM correlators using integrability

Regular Seminar Zahra Zahraee (CERN)

at:
14:00 QMUL
room Zoom
abstract:

In this talk we use integrability data to bootstrap correlation functions of planar maximally supersymmetric Yang- Mills theory. Focusing on four-point correlation function of stress-tensor, we first introduce a set of sum rules that are only sensitive to single-traces in the OPE expansion (this is advantageous because this data is available from integrability). We then discuss how these sum rules can be employed in numerical bootstrap to nonperturbatively bound planar OPE coefficients. We show rigorous bounds for the OPE coefficient of the Konishi operator at various t’Hooft couplings outside the perturbative regime. The talk is based on an ongoing work and 2207.01615.

18.04.2024 (Thursday)

Gravitational Wave Initiative

Conference Inaugural meeting (Queen Mary University)

at:
10:00 QMUL
room Social Hub SMS
abstract:

https://sites.google.com/view/gwiinauguralmeeting/home

11.04.2024 (Thursday)

Perturbed Black Holes: A CFT Approach and the Kerr-Binary-Problem

Regular Seminar Fabian Bautista (IPhT)

at:
14:00 QMUL
room G. O. Jones 610 and Zoom
abstract:

In this talk we will discuss a new window into the solution of Heun differential equations arising in black hole perturbation theory using the tools of two-dimensional conformal field theory and gauge theories. Kerr Compton amplitudes for massless perturbation of generic spin-weight s, are written in compact form in terms of the so-called Nekrasov-Shatashvili functions; their symmetry properties are also discussed. These are then used as building blocks to study the scattering of two Kerr black holes with generic spin orientation. Comparison to conservative observables for bounded systems computed via first-order gravitational self-force methods are shown.

04.04.2024 (Thursday)

The NLO Scattering Waveform and Linear-in-Spin Corrections

Regular Seminar Lara Bohnenblust (University of Zurich)

at:
14:00 QMUL
room G. O. Jones 610 and Zoom
abstract:

Next-generation gravitational-wave detectors, operating in lower frequency ranges, will explore new types of systems including fly-bys, captures, eccentric configurations and high spin, that are well described within a weak-field approximation. I will discuss our recent NLO waveform computation for black-hole scattering in the Post-Minkowskian approximation, including linear-in-spin corrections, following Ref. [2312.14859]. The result is obtained from five point one-loop scattering amplitudes including massive scalars, vectors and a graviton, and computations are performed in the numerical unitarity framework. Special emphasis is put on the treatment of the "cut term" in the observable-based approach of Kosower, Maybee and O’Connell. The result includes IR and UV divergences and I will explain their origin and their treatment to obtain a finite observable.

26.03.2024 (Tuesday)

Entanglement, soft modes and celestial holography

Exceptional Seminar Ana-Maria Raclariu (Amsterdam University)

at:
14:00 QMUL
room SMS MB-503
abstract:

In this talk I will start by revisiting the calculation of entanglement entropy in free Maxwell theory in 3+1 dimensional Minkowski spacetime. I will characterize the soft sector associated with a subregion and demonstrate that conformally soft mode configurations at the entangling surface, or equivalently correlated fluctuations in the large gauge charges of the subregion and its complement, give a non-trivial contribution to the entanglement entropy across a cut of future null infinity. I will conclude with some comments on the holographic description of bulk subregions in asymptotically flat spacetimes.

21.03.2024 (Thursday)

Cosmological Correlators in Momentum Space

Regular Seminar Chandramouli Chowdhury (University of Southampton)

at:
14:00 QMUL
room G. O. Jones 610 and Zoom
abstract:

Cosmological Correlators are one of the physical quantities that are of interest to cosmologists and are also of theoretical interest as they are related to CFT correlators via the AdS/CFT correspondence. These differ from the S-matrix as they are correlation functions computed on a given time slice. In this talk, I will review some progress in computing these in momentum space and also describe its relation to the S-matrix.

13.03.2024 (Wednesday)

The view of a point: Wigner-Inonu contractions and the flat space limit of AdS scattering

Triangular Seminar David Berenstein (UCSB)

at:
15:00 QMUL
room David Sizer Lecture Theatre
abstract:

I will describe how to consider the flat space limit of scaterig in AdS relative to a point (where sacttering occurs). The kinematics is related to the Wigner-Inonu contraction. In particular, I will discuss how to take the proper limits of wave functions in AdS (times extra dimensions) to understand a notion of in states and out states and how a scattering amplitude should be conceived. This will make use of the embedding formalism, where the description of these wave functions is simple. I will show how these wave functions are related to other constructions in AdS/CFT and suggest how the Mellin parameters of these other setups arise from integral representations of the wave functions in terms of Schwinger parameters.

13.03.2024 (Wednesday)

Vertex algebras in SUSY QFT across dimensions

Triangular Seminar Mykola Dedushenko (Simons Center for Geometry and Physics)

at:
16:30 QMUL
room David Sizer Lecture Theatre
abstract:

I will describe a construction relating the Vertex Operator Algebra (VOA) of a 4d N=2 superconformal field theory (SCFT) to the boundary VOA in 3d N=4 QFT, and to the VOA in 2d QFT. Besides unifying several known constructions, this also draws connections to many other interesting problems, among which are the novel rank-zero 3d N=4 SCFTs emerging in the high-temperature limit of a 4d SCFT "on the second sheet".

12.03.2024 (Tuesday)

MTC(M3,G): 3d Topological Order Labeled by Seifert Manifolds

Exceptional Seminar Jingxiang Wu (Oxford)

at:
15:00 QMUL
room GO Jones 610
abstract:

We propose a correspondence between topological order in 2+1d and Seifert three-manifolds together with a choice of ADE gauge group G. Topological order in 2+1d is known to be characterised in terms of modular tensor categories (MTCs), and we thus propose a relation between MTCs and Seifert three-manifolds. The correspondence defines for every Seifert manifold and choice of G a fusion category, which we conjecture to be modular whenever the Seifert manifold has trivial first homology group with coefficients in the centre of G. The construction determines the spins of anyons and their S-matrix, and provides a constructive way to determine the R- and F-symbols from simple building blocks. We explore the possibility that this correspondence provides an alternative classification of MTCs, which is put to the test by realising all MTCs (unitary or non-unitary) with rank r<=5 in terms of Seifert manifolds and a choice of Lie group G.

07.03.2024 (Thursday)

Geometric conservation in curved spacetime and entropy

Regular Seminar Sinya Aoki (Kyoto University)

at:
14:00 QMUL
room G. O. Jones 610 and Zoom
abstract:

In this talk, I provide an improved definition of new conserved quantities derived from the energy-momentum tensor in curved spacetime by introducing an additional scalar function. I find that the conserved current and the associated conserved charge become geometric under a certain initial condition of the scalar function, and show that such a conserved geometric current generally exists in curved spacetime. Furthermore, I demonstrate that the geometric conserved current agrees with the entropy current for the perfect fluid, thus the conserved charge is the total entropy of the system.

29.02.2024 (Thursday)

Bounding Effective Field Theories: From flat space to FRW

Regular Seminar Mariana Carrillo Gonzales (Imperial College)

at:
14:00 QMUL
room G. O. Jones 610 and Zoom
abstract:

Effective Field Theories (EFTs) allow us to describe low energy physics without knowing the specific UV completion. This comes at the cost of having free parameters (Wilson coefficients) whose values encode the UV physics, but are not constraint from a standard EFT point of view. It is well known that some values can lead to unphysical properties of these theories. In this talk, I will present a low energy technique to put bounds on these coefficients by requiring causal propagation. I will show how these bounds can be obtained in flat space and then move on to how apply these techniques in cosmological spacetimes. Throughout the talk I will present bounds on scalar and photon EFTs.

22.02.2024 (Thursday)

Twisting integrability

Regular Seminar Sibylle Driezen (ETH Zurich)

at:
14:00 QMUL
room G. O. Jones 610 and Zoom
abstract:

Recent years have seen an upsurge of interest in deformations of two-dimensional sigma-models which preserve classical integrability. Integrability is known to offer powerful techniques for solving such models exactly, even in complex scenarios such as at strong coupling. This talk introduces classical integrability, and the role played by worldsheet dualities in the development of a large family of integrable deformations. The second part of the talk focuses on the application of these deformations within the AdS/CFT correspondence, in order to obtain exact methods for addressing gauge and gravity theories with reduced Noether (super)symmetries. However, current "AdS/CFT integrability" methods are mostly restricted to the undeformed, maximally (super)symmetric instances. To enhance their applicability to a broader range of theoretical models, the concept of “twisted” AdS/CFT integrability is introduced, specifically targeting the “Jordanian” subclass of integrable deformations. Recent and ongoing work in this area will be discussed.

15.02.2024 (Thursday)

Kerr binary dynamics from minimal coupling and double copy

Regular Seminar Francesco Alessio (Nordita)

at:
14:00 QMUL
room G. O. Jones 610 and Zoom
abstract:

I will show how to construct a Lagrangian based on a notion of minimal coupling that includes classical spin effects that is relevant to describe Kerr binaries in the post-Minkowski (PM) regime. Using such Lagrangian, I will derive expressions for the classical amplitude for the elastic 2—>2 process at 1PM and 2PM. I will then consider radiation reaction effects and their connection to the imaginary part of the 3PM spinning eikonal phase.