Directions

Imperial College has its own detailed information on general directions and on getting to the theoretical physics group. The College is located on Prince Consort Road, south of Hyde Park (map). The most convenient access is via tube (South Kensington, Gloucester Road) or buses. The Theoretical Physics group resides on the 5th floor of the Huxley Building. The group also possesses its own description.

Seminars at Imperial College

Found at least 20 result(s)

08.09.2020 (Tuesday)

Entanglement entropies of equilibrated pure states in quantum many-body systems and replica wormholes

Informal Seminar Hong Liu (MIT)

at:
14:00 IC
room online - instructions in abstract
abstract:

We develop a universal approximation for the Renyi entropies of a pure state at late times in non-integrable systems, which macroscopically resembles an equilibrium density matrix. The resulting expressions are fully determined by properties of the associated equilibrium density matrix, and are hence independent of the details of the initial state, while also being manifestly consistent with unitary time-evolution. For equilibrated pure states in gravity systems, such as those involving black holes, this approximation gives a prescription for calculating entanglement entropies using Euclidean path integrals which is consistent with unitarity and hence can be used to address the information loss paradox of Hawking. Applied to recent models of evaporating black holes and eternal black holes coupled to baths, it provides a derivation of replica wormholes, and elucidates their mathematical and physical origins. In particular, it shows that replica wormholes can arise in a system with a fixed Hamiltonian, without the need for ensemble averages. ----- Follow the usual link or contact the organisers (Antoine Bourget and Edoardo Vescovi).

04.08.2020 (Tuesday)

Gravity/Ensemble Duality

Informal Seminar Elizabeth Wildenhain (University of California, Berkeley)

at:
16:00 IC
room online - instructions in abstract
abstract:

For the first time, a gravitational calculation was recently shown to yield the Page curve for the entropy of Hawking radiation, consistent with unitary evolution. However, the calculation takes as essential input Hawking's result that the radiation entropy becomes large at late times. We call this apparent contradiction the state paradox. We exhibit its manifestations in standard and doubly-holographic settings, with and without an external bath. We clarify which version(s) of the Ryu-Takayanagi prescription apply in each setting. We show that the two possible homology rules in the presence of a braneworld generate a bulk dual of the state paradox. The paradox is resolved if the gravitational path integral computes averaged quantities in a suitable ensemble of unitary theories, a possibility supported independently by several recent developments. ----- Follow the usual link or contact the organisers (Antoine Bourget and Edoardo Vescovi).

28.07.2020 (Tuesday)

Wormholes and branes in JT gravity

Informal Seminar Andreas Blommaert (Ghent University)

at:
14:00 IC
room online - instructions in abstract
abstract:

I will highlight the role of wormholes and branes in reconciling semiclassical gravitational (black hole) physics with unitary quantum mechanical evolution. Most of the talk will be based on recent developments in JT gravity. This is a model of quantum gravity in two dimensions which is analytically tractable. I will first explain why we need wormholes in order to capture late time properties of chaotic quantum systems from a geometrical point of view. I then point out that naively the inclusion of wormholes in a gravitational theory comes with an ensemble interpretation of said gravitational theory. Finally I will explain how this conclusion (that gravity is an ensemble) can be avoided by including branes in the bulk geometrical description. These branes can encode the micro structure of a given unitary quantum system in bulk geometry. ----- Follow the usual link or contact the organisers (Antoine Bourget and Edoardo Vescovi).

21.07.2020 (Tuesday)

Superconformal RG Interfaces in Holography

Informal Seminar Matthew Cheung (Imperial College London)

at:
14:00 IC
room online - instructions in abstract
abstract:

Defects/interfaces/boundaries are interesting objects to study in QFT, and one powerful way to study them is via the use of holography. In this talk, I will discuss our construction of gravitational solutions that holographically describe two different 4d SCFTs joined together at a co-dimension one, planar RG interface and preserving 3d superconformal symmetry. The RG interface we have constructed joins the 4d N=4 SYM theory on one side with the N=1 Leigh-Strassler SCFT on the other. These solutions in general are associated with spatially dependent mass deformations on the N=4 SYM side, but there is a particularly interesting solution for which these deformations vanish. If time allows, I will also discuss another example of our work involving ABJM theory and two 3d N=1 SCFTs with G_2 symmetry. This talk is based on the work hep-th/2007.07891 with Igal Arav, Jerome Gauntlett, Matt Roberts and Chris Rosen. ----- Follow the usual link or contact the organisers (Antoine Bourget and Edoardo Vescovi).

23.06.2020 (Tuesday)

Challenging the Inflationary Paradigm

Regular Seminar Eugene Lim (King's College London)

at:
13:30 IC
room online - instructions in abstract
abstract:

Inflation is now the paradigmatic theory of the Big Bang. But is it deserved? I will describe the conceptual and theoretical challenges that Inflation is still facing, argue that we should keep an open mind. In particular, I will argue that while it is a theory that claims to be a theory of initial conditions of the Universe, successful inflation actually depends on an intimate interplay between its own initial conditions and the inflationary model. I will show how one might go about probing this interplay by testing whether inflation can begin if its own initial conditions are not homogenous. ----- Follow the usual link or contact the organisers (Antoine Bourget and Edoardo Vescovi). Student introduction at 13:00.

17.06.2020 (Wednesday)

On higher-spin theory in two dimensions

Regular Seminar Xavier Bekaert (Tours (France))

at:
14:00 IC
room Zoom
abstract:

We aim at formulating a higher-spin gravity theory around AdS2 relevant for holography. As a first step, we investigate its kinematics by identifying the low-dimensional cousins of the standard higher-dimensional structures in higher-spin gravity such as the singleton, the higher-spin symmetry algebra, the higher-rank gauge and matter fields, etc.

11.06.2020 (Thursday)

Supersymmetric S-folds

Regular Seminar Adolfo Guarino (Oviedo)

at:
15:45 IC
room Zoom
abstract:

I will discuss recent progress towards understanding geometric and holographic aspects of electromagnetic duality in four-dimensional supergravity. More concretely, I will focus on the connection between electromagnetic duality and the existence of new classes of supersymmetric S-fold backgrounds of type IIB supergravity. These provide natural candidates to holographically describe new strongly coupled three-dimensional CFT’s which are localised on interfaces of N=4 super-Yang-Mills theory.

09.06.2020 (Tuesday)

A Quantum Lab for Quantum Field Theory

Regular Seminar Steven Abel (Durham University)

at:
13:30 IC
room online - instructions in abstract
abstract:

In this pedagogical talk I will discuss recent and ongoing work showing how quantum field theory problems can be embedded on to quantum annealers. The general method we use is a discretisation of the field theory problem into a general Ising model, with the continuous field values being encoded into Ising spin chains. To illustrate the method, and as a simple proof of principle, we have used a quantum annealer to recover the correct profile of various tunnelling solutions. Then I will discuss current work where we construct actual quantum tunnelling processes involving instantons. These methods are applicable to many nonperturbative problems. ----- Follow the usual link or contact the organisers (Antoine Bourget and Edoardo Vescovi).

03.06.2020 (Wednesday)

Spherical Branes, Supersymmetric Localization, and Holography

Regular Seminar Nikolay Bobev (KUL Leuven)

at:
14:00 IC
room Zoom
abstract:

I will describe a class of supergravity solutions holographically dual to d-dimensional maximally supersymmetric SYM on S^d. Supersymmetric localization can be employed to calculate the partition function and the VEV of a 1/2-BPS Wilson lines in the planar limit of the SYM theory. I will present the results of this calculation and will show how they lead to a non-trivial precision test of holography in the context of non-conformal QFTs and space-times that are non asymptotically locally AdS.

26.05.2020 (Tuesday)

Constraining Modified Gravity Models with Casimir Force Experiments

Regular Seminar Anne-Christine Davis (University of Cambridge)

at:
13:30 IC
room online - instructions in abstract
abstract:

Modified gravity models have been developed to try to explain the observed acceleration of the expansion of the Universe. Such models introduce and extra, fifth force, and usually employ a screening mechanism whereby the fifth force is screened in the solar system but unscreened cosmologically. Recent developments in laboratory experiments mean that such theories can now be tested and constrained using existing experiments. In particular innovative Casimir force experiments can be used to constrain such theories. This enables Einstein gravity to be tested on scales not previously explored. ----- Follow the usual link or contact the organisers (Antoine Bourget and Edoardo Vescovi). Student introduction at 13:00.

20.05.2020 (Wednesday)

TBA

Regular Seminar Yang-Hui He (Oxford)

at:
14:00 IC
room Online Seminar Room
abstract:

TBA

19.05.2020 (Tuesday)

The classical double copy

Regular Seminar Chris White (Queen Mary, University of London)

at:
13:30 IC
room online - instructions in abstract
abstract:

Non-abelian gauge theories underly particle physics, including collision processes at particle accelerators. Recently, quantum scattering probabilities in gauge theories have been shown to be closely related to their counterparts in gravity theories, by the so-called "double copy". This suggests a deep relationship between two very different areas of physics, and may lead to new insights into quantum gravity, as well as novel new computational methods. This talk will review the double copy for amplitudes, before discussing how it may be extended to describe exact classical solutions such as black holes. I will then look at recent work which aims to generalise the double copy yet further, and conclude with an outlook of current open problems. ----- Follow the usual link or contact the organisers (Antoine Bourget and Edoardo Vescovi). Student introduction at 13:00.

13.05.2020 (Wednesday)

(Quantum) Higher Spin Gravity and Physics

Regular Seminar Evgeny Skvortsov (Albert Einstein Institute (Potsdam))

at:
14:00 IC
room Online Seminar Room
abstract:

I will give a general overview of Higher Spin Gravities and also discuss the recent developments that give a class of models where UV-divergences of Einstein gravity cancel out thanks to the higher spin symmetry. At the end I will discuss the relation between Higher Spin Gravities and a class of conformal field theories in three dimensions that describe the physics of many second order phase transitions in the real world and have been recently conjectured to exhibit a number of remarkable dualities, in particular the three-dimensional bosonization duality. I will show how Higher Spin Gravity can help to prove the dualities and how it makes new predictions. The relation to QCD and self-dual Yang-Mills will also be discussed.

12.05.2020 (Tuesday)

Phenomenological Applications of the EFTs for Condensed Matter

Regular Seminar Angelo Esposito (Ecole polytechnique federale de Lausanne)

at:
13:30 IC
room online - instructions in abstract
abstract:

In this talk I will review the general ideas behind the recently developed relativistic effective field theories (EFTs) for different phases of matter (spontaneous symmetry breaking, Goldstone theorem, etc.). I will put particular emphasis on concretely building an EFT for the description of collective excitations in zero-temperature superfluids, which is the simplest of these theories. I will then argue that these methods, borrowed from high energy theory ideology, are mature enough to be successfully applied to phenomenologically relevant problems. In this direction, I will present two applications: (1) the calculation of the gravitational mass transported by a sound wave in a nonrelativistic medium (superfluid, fluid and solid), and (2) the study of the response of a He-4 detector to the passage of sub-MeV dark matter particle. ----- Follow the link in use since May 5th or contact the organisers (Antoine Bourget and Edoardo Vescovi). Student introduction at 13:00.

05.05.2020 (Tuesday)

Inflation and Geometry

Regular Seminar Sebastien Renaux-Petel (Institut d'Astrophysique de Paris)

at:
13:30 IC
room online - instructions in abstract
abstract:

Inflation, an era of accelerated expansion of the universe prior to the radiation phase, constitutes the paradigm of primordial cosmology. Within this paradigm, the simplest single-field slow-roll models economically explain all current data. However, the sensitivity of inflation to Planck scale physics, and the fact that ultraviolet completions of inflation invariably involve extra fields coupled to the inflaton, indicate that these models constitute at best a phenomenological description that emerges from a more realistic physical framework. In this talk, I will describe recent works that aim at understanding the consequences of the presence of several degrees of freedom during inflation. In particular, I will highlight that realistic models are characterized not only by their potentials but also by the internal geometries in which the fields live in, and I will discuss related novel phenomena that have been studied in the past years. ----- Contact the organisers (Antoine Bourget and Edoardo Vescovi) for the link.

28.04.2020 (Tuesday)

Bootstrapping Cosmological Correlations

Regular Seminar Daniel Baumann (University of Amsterdam)

at:
13:30 IC
room online - instructions in abstract
abstract:

The past decade has seen an explosion of progress in our understanding of scattering amplitudes in gauge theory and gravity. New bootstrap methods have revealed hidden symmetries and new mathematical structures that are completely invisible in the standard approach of Lagrangians and Feynman diagrams. Inspired by these developments, the bootstrap philosophy has recently been applied to cosmology. In this talk, I will describe our work on the bootstrapping of cosmological correlations. The talk will have two parts: In the first part, I will describe the conceptual foundations of the "cosmological bootstrap" as developed together with Arkani-Hamed, Lee and Pimentel in [arXiv:1811.00024]. In the second part, I will describe the extension of these ideas to massless particles with spin, where locality provides important new constraints. This is work to appear with Duaso Pueyo, Joyce, Lee and Pimentel. ----- Contact the organisers (Antoine Bourget and Edoardo Vescovi) for the link.

27.02.2020 (Thursday)

Holographic Uhlmann Holonomy and the Entanglement Wedge Symplectic Form

Regular Seminar Josh Kirklin (University of Cambridge)

at:
14:00 IC
room GO Jones 610
abstract:

Subregion duality is an idea in holography which states that every subregion of the boundary theory has a corresponding subregion in the bulk theory, called the 'entanglement wedge', to which it is dual. In the classical limit of the gravity theory, we expect the fields in the entanglement wedge to permit a Hamiltonian description involving a phase space and Poisson brackets. In this talk, I will describe how this phase space arises from the point of view of the boundary theory. In particular, I will explain how it emerges from measurements of a certain quantum information-theoretic quantity, known as the 'Uhlmann phase', in the boundary subregion.

18.02.2020 (Tuesday)

Some impractical practicalities of the SMEFT

Regular Seminar Michael Trott (Niels Bohr Institute)

at:
13:30 IC
room H503
abstract:

In recent years the use of effective field theory techniques has come to the fore when studying the LHC data set. This approach constrains the possible effects of physics beyond the Standard Model, by constraining small modifications of Standard Model interactions in a theory known as the Standard Model Effective Field Theory. Although highly practical and agnostic, the presence of a Higgs field that takes on a background expectation value leads to some unique challenges in formulating this effective field theory and interfacing the SMEFT with the data. We will review some of the successes of this approach and some of the problems that have appeared. A growing understanding of the physics of the SMEFT as emerging from the geometry of Higgs field space offers great potential to tackle some of the remaining challenges. We will also introduce and discuss this approach.

12.02.2020 (Wednesday)

TBA

Regular Seminar Evgeny Sobko (Southampton)

at:
14:00 IC
room H503
abstract:

TBA

11.02.2020 (Tuesday)

Learning about the Planck scale: Marginal couplings and the predictive power of scale invariance

Regular Seminar Aaron Held (Imperial College London)

at:
13:30 IC
room H503
abstract:

I will review the current status of the asymptotic safety program, focusing on the predictive power of scale invariance, followed by a collection of results on how the Standard-Model couplings may be used to constrain physics at the Planck scale. At a time in which collider measurements collect increasing evidence that the Standard Model as an effective field theory is consistent up to the Planck scale, its marginal couplings offer a unique opportunity to learn about quantum gravity. I will also briefly introduce a research program aimed at constraining the marginal couplings of the gravitational sector, i.e., curvature-squared terms, via black-hole stability and binary mergers.