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)

03.05.2017 (Wednesday)

Diffusion and chaos in holographic systems at non-zero density

Regular Seminar Richard Davison (Harvard)

at:
14:00 IC
room H503
abstract:

Recent work has uncovered relations between the rate at which chaotic behaviour spreads in strongly interacting quantum systems, and the diffusivities of certain processes in these systems. Focusing mainly on holographic examples, I will explore the extent to which these relations hold in states at non-zero density, where the diffusion of charge and energy are no longer independent processes.

05.04.2017 (Wednesday)

Supersymmetric microstate geometries

Regular Seminar Harvey Reall (Cambridge)

at:
14:00 IC
room H503
abstract:

A microstate geometry is a smooth, time-independent, asymptotically flat, horizon-free solution of type IIB supergravity. According to the “fuzzball" conjecture, such solutions describe individual microstates of black holes. Non-supersymmetric microstate geometries typically suffer from linearized instabilities. I will argue that supersymmetric microstate geometries suffer from a nonlinear instability. I will also discuss how such solutions lead to a new type of mathematical structure, so-called “ambipolar” hyperkahler manifolds, and explain how such manifolds can be constructed.

29.03.2017 (Wednesday)

Yang-Baxter strings, twists, and AdS/CFT

Regular Seminar Stijn van Tongeren (Humboldt U.)

at:
14:00 IC
room H503
abstract:

The appearance of integrability in the duality between the AdS5xS5 string and planar maximally supersymmetric Yang-Mills theory gives rise to many insightful results. Various deformations of this AdS/CFT dual pair are known to also be integrable, prompting the question how far the power of integrability extends in this setting. In recent years there has been a lot of progress in answering this question. Rather than trying to demonstrate integrability in known AdS/CFT dual pairs, efforts instead focused on finding manifestly integrability preserving deformations of the AdS5xS5 string. While constructed to preserve integrability, the resulting so-called Yang-Baxter sigma models are, however, not guaranteed to describe strings, or have an AdS/CFT interpretation. The former of these points has since been addressed and turns out to be closely related to (nonabelian) T duality, and we now understand which of these models continue to describe strings. The goal of my talk is to address the latter point, regarding the AdS/CFT interpretation of these models. I will use symmetry considerations to give a unified AdS/CFT picture for these Yang-Baxter strings as duals to various noncommutative deformations of supersymmetric Yang-Mills theory. My general conjecture matches many known dualities, and I will briefly discuss nontrivial tests in various new cases, in the form of brane constructions indicating the desired dualities.

23.03.2017 (Thursday)

The a-function in 3 dimensions

Regular Seminar Ian Jack (Liverpool)

at:
13:00 IC
room H503
abstract:

The a-theorem expressing the monotonicity of renormalisation group flows in four (and other even) dimensions is now well-accepted. There is a function (the a-function) generating the RG beta-functions as a gradient flow via a positive-definite metric. However the standard definition of the a-function in terms of the trace anomaly of the energy-momentum tensor does not work in odd dimensions. In this talk we focus on the gradient-flow property of the a-function and show that a function with similar properties can be constructed order-by-order in three dimensions. We start by reviewing the a-function in even dimensions from a gradient-flow standpoint. Then we discuss our explicit calculations in three dimensions. Finally we present some progress towards relating our results to the F-function which has been shown to have the expected monotonicity properties at fixed points.

16.03.2017 (Thursday)

Quantum Geometry and Non-Geometric Backgrounds

Exceptional Seminar Richard Szabo (Heriot-Watt U.)

at:
13:00 IC
room H503
abstract:

Recent advances in non-geometric string theory suggest that locally non-geometric flux compactifications can be understood in terms of nonassociative deformations of spacetime geometry. We will review some of these developments and how they shed light on properties of non-geometric strings, and explain some new results concerning how these structures lift to non-geometric M-theory.

15.03.2017 (Wednesday)

Algebraic properties of the monopole formula

Regular Seminar Marcus Sperling (Vienna U.)

at:
14:00 IC
room H503
abstract:

In this talk, I will discuss how the two geometric notions "fan" and "monoid" can be very fruitful for the understanding of the monopole formula for 3d N=4 gauge theories. After a brief reminder of the monopole formula, I will introduce the matter fan and reorganise the monopole formula accordingly. I then discuss the resulting benefits such as: (1) Explicit expressions for the Hilbert series built from well-studied constituents. (2) Proof that the order of the pole at t=1 and t → ∞ equals the complex or quaternionic dimension of the Coulomb branch. (3) Identification of a sufficient set of chiral ring generators.

08.03.2017 (Wednesday)

Localization of supersymmetric field theories on non-compact hyperbolic three-manifolds

Regular Seminar Daisuke Yokoyama (King's College London)

at:
14:00 IC
room H503
abstract:

I am going to talk about how to derive an exact partition function of supersymmetric field theories on a supersymmetry-preserving quotient of Euclidean AdS_3 by localization. This is one of first examples about localization on non-compact spaces. I will describe the situation by comparing it to a situation in compact spaces. Then, I will explain how to perform a localization procedure on the manifold, and finally, I will discuss the features of the partition function we derived.

22.02.2017 (Wednesday)

Polygon Seminar: E Theory

Triangular Seminar Peter West (King's College London)

at:
15:00 IC
room Huxley 140
abstract:

I review the theory of non-linear realisations and Kac-Moody algebras, I explain how to construct the non-linear realisation based on the Kac-Moody algebra $E_{11}$ and its vector representation. I explain how this field theory leads to dynamical equations which contain an infinite number of fields defined on a spacetime with an infinite number of coordinates. I then show that these unique dynamical equations, when truncated to low level fields and the usual coordinates of spacetime, lead to precisely the equations of motion of eleven dimensional supergravity theory. By taking different group decompositions of $E_{11}$ we find all the maximal supergravity theories, including the gauged maximal supergravities, and as a result the non-linear realisation is a unified theory that is the low energy effective action for type II strings and branes. These results essentially confirm the $E_{11}$ conjecture given many years ago.

15.02.2017 (Wednesday)

The holographic Weyl semi-metal

Regular Seminar Karl Landsteiner (Madrid, IFT)

at:
14:00 IC
room H503
abstract:

Weyl semi-metals are an exciting new class of 3D materials with exotic transport properties. They are characterised by point like singularities in the Brillouin zone at which conduction and valence bands touch. Around these points the electronic quasi-particle excitations can be described by either left- or right-handed Weyl spinors. This makes high energy physics to be the low energy electronics of these materials. Holographic models might be useful in two ways: first some Weyl semi-metals might be strongly interacting and second holography is our best tool to understand and discover new exotic transport properties related to the chiral nature of the charge carriers, especially to chiral anomalies. I will review the construction of a holographic model supporting a topological quantum phase transition between a topological Weyl semi-metal phase and a trivial phase and use it to predict the existence of a new dissipation less form of viscosity (Hall viscosity) in the quantum critical region.

08.02.2017 (Wednesday)

Semiclassics, Goldstone Bosons and CFT data

Regular Seminar Alexander Monin (Ecole Polytechnique, Lausanne)

at:
14:00 IC
room H503
abstract:

In a generic CFT the spectrum of operators carrying a large U(1) charge can be analyzed semiclassically in an expansion in inverse powers of the charge. The key is the operator state correspondence by which such operators are associated with a finite density superfluid phase for the theory quantized on the cylinder. The dynamics is dominated by the corresponding Goldstone hydrodynamic mode and the derivative expansion coincides with the inverse charge expansion. I will illustrate this situation by first considering simple quantum mechanical analogues and then will systematize the approach by employing the coset construction for non-linearly realized space-time symmetries. Focussing on CFT3 I will illustrate that the three point function coefficients turn out to satisfy universal scaling laws and correlations as the charge and spin are varied.

02.02.2017 (Thursday)

Localised Black Holes and Precision Holography

Regular Seminar Jorge Santos (DAMTP)

at:
13:00 IC
room H503
abstract:

We numerically construct asymptotically global AdS_5 x S^5 black holes that are localised on the S^5. These are solutions to type IIB supergravity with S^8 horizon topology that dominate the microcanonical ensemble at small energies. At higher energies, there is a first-order phase transition to AdS_5-Schwarzschild x S^5. By the Anti-de Sitter/Conformal Field Theory (AdS/CFT) correspondence, this transition is dual to spontaneously breaking the SO(6) R-symmetry of N=4 supersymmetric Yang-Mills down to SO(5). We extrapolate the location of this phase transition and compute the expectation value of a scalar operator in the low energy phase. In addition, we discuss the construction of localised black holes in type IIA, which are dual (via T-duality) to the low temperature phase of thermal 1+1 dimensional supersymmetric Yang-Mills theory on a circle.

25.01.2017 (Wednesday)

Universal Formula for the Holographic Speed of Sound

Regular Seminar Andres Anabalon (Adolfo Ibanez U.)

at:
14:00 IC
room H503
abstract:

We consider planar hairy black holes in five dimensions with a real scalar field in the Breitenlohner-Freedman window. We show that is possible to derive a universal formula for the speed of sound for any theory. As an example we find all the planar black holes of the single scalar field consistent truncation of type IIB that preserves the SO(3)×SO(3) R-symmetry group of the gauge theory. We find the speed of sound for different values of the induced vacuum expectation value when a double trace deformation is induced in the gauge theory. For any theory, we show that the speed of sound is not bounded by any special value.

19.01.2017 (Thursday)

6d Dual Conformal Symmetry and Minimal Volumes in AdS

Regular Seminar Arthur Lipstein (Durham)

at:
13:00 IC
room H503
abstract:

The planar scattering amplitudes of 4d N = 4 super Yang-Mills theory and 3d N=6 Chern-Simons theory exhibit a remarkable property known as dual conformal symmetry. Motivated by this, we investigate the consequences of dual conformal symmetry in six dimensions. We find that 6d dual conformal symmetry fixes the structure of the one-loop 4-point amplitude and suggests a Lagrangian with more than two derivatives. Moreover, we obtain a similar structure by generalizing the Alday-Maldacena solution for a string in Anti-de Sitter space to a 2-brane ending on a pillow-shaped surface in the boundary whose seams correspond to a null-polygon, which suggests an all-loop formula for the 4-point amplitude similar to that of N=4 super Yang-Mills theory.

14.12.2016 (Wednesday)

On branes and instantons

Regular Seminar Ruben Minasian (IPhT Saclay)

at:
14:00 IC
room H503
abstract:

I’ll review old and new aspects of deformed instanton equations derived from D-branes.

08.12.2016 (Thursday)

Classification of surface defects from Little Strings

Regular Seminar Nathan Haouzi (UC Berkeley)

at:
13:00 IC
room H503
abstract:

The so-called 6d (2,0) conformal field theory in six dimensions, labeled by an ADE Lie algebra, has become of great interest in recent years. Most notably, it gave new insights into lower dimensional supersymmetric field theories, for instance in four dimensions, after compactification. In this talk, I will talk about a deformation of this CFT, the six-dimensional (2,0) little string theory: its origin lies in type IIB string theory, compactified on an ADE singularity. We further compactify the 6d little string on a Riemann surface with punctures. The resulting defects are D-branes that wrap the 2-cycles of the singularity. This construction has many applications, and I will focus on one: I will provide the little string origin of the classification of surface defects of the 6d (2,0) CFT, for ADE Lie algebras. Furthermore, I will give the physical realization of the so-called Bala-Carter labels that classify nilpotent orbits of these Lie algebras.

01.12.2016 (Thursday)

Localised Black Holes and Precision Holography

Regular Seminar Jorge Santos (Cambridge)

at:
13:00 IC
room H503
abstract:

We numerically construct asymptotically global AdS_5xS^5 black holes that are localised on the S^5. These are solutions to type IIB supergravity with S^8horizon topology that dominate the microcanonical ensemble at small energies. At higher energies, there is a first-order phase transition to AdS_5-Schwarzschild x S^5. By the Anti-de Sitter/Conformal Field Theory (AdS/CFT) correspondence, this transition is dual to spontaneously breaking the SO(6) R-symmetry of N=4 supersymmetric Yang-Mills down to SO(5). We extrapolate the location of this phase transition and compute the expectation value of a scalar operator in the low energy phase. In addition, we discuss the construction of localised black holes in type IIA, which are dual (via T-duality) to the low temperature phase of thermal 1+1 dimensional supersymmetric Yang-Mills theory on a circle.

23.11.2016 (Wednesday)

SEMINAR CANCELLED

Regular Seminar Paul Townsend (Cambridge)

at:
14:00 IC
room H503
abstract:

The N-extended massless superparticle in a 4D Minkowski background has a worldline time-reversal invariance that becomes CPT in the quantum theory. This symmetry is anomalous for odd N, which explains why there is no CPT-self-conjugate massless supermultiplet for N=1. In the supertwistor formulation of superparticle mechanics, the anomaly is a close cousin of the parity anomaly of 3D gauge theories. CPT is not anomalous if N is even but if 2N is odd there is a Kramers degeneracy, which explains why the N=2 hypermultiplet is a doubled version of the CPT-self-conjugate supermultiplet of helicities (-1/2,0,0,1/2).

21.11.2016 (Monday)

Tinkertoys for the Exceptional (2,0) Theories

Exceptional Seminar Jacques Distler (Texas U.)

at:
13:00 IC
room H503
abstract:

I'll give an introduction to N=2, D=4 SCFTs of "Class-S" and a survey of our programme for classifying such theories. I will put special emphasis on the theories arising from the Exceptional (2,0) SCFTs in D=6.

17.11.2016 (Thursday)

Recent Advances in Heterotic Moduli

Regular Seminar Eirik Eik Svanes (Paris, LPTHE)

at:
13:00 IC
room H503
abstract:

I will discuss recent advances in addressing the heterotic moduli problem in six and seven dimensions. To map out the reduction to a lower dimensional effective theory, and in a quest to complete our understanding of the generically torsional geometries that appear, it is important to understand the moduli of these geometries. I will briefly review the infinitesimal moduli space in six dimensions, and comment on some recent advances in understanding its geometric properties. I will then explain how a similar story is emerging in seven dimensional compactifications on more exotic manifolds with G2-structure, giving hope that similar tools can be applied to understand moduli in other areas of string theory, with possible applications to phenomenology and AdS/CFT. If time, I will comment on some recent advances is studying finite deformations and obstructions of the moduli space.

10.11.2016 (Thursday)

A magnetically induced quantum critical point in holography

Exceptional Seminar Olga Papadoulaki (Utrecht)

at:
13:00 IC
room H503
abstract:

Abstract: We are using holography to study quantum phase transitions in a 2+1 D strongly coupled non conformal gauge theory at finite chemical potential and magnetic field B. Our gravity dual is 4D N = 2 Fayet-Iliopoulos gauged supergravity. We found a line of quantum critical points at B= Bc between extremal dyonic black branes and extremal magnetically charged "thermal gas" solutions. We will introduce the two types of solutions, their thermodynamics and their phase diagram. Then we will discuss the physics of the critical point and we will point out qualitative similarities between our field theory and Nambu- Jona- Lasinio model in 2+1 D under the presence of an external magnetic field. We will conclude with some open questions both on the gravity and field theory side and we will discuss future directions.