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)

10.02.2016 (Wednesday)

From holographic transport at finite coupling to bounds on conductivities at strong disorder

Regular Seminar Saso Grozadanov (Leiden)

at:
14:00 IC
room H503
abstract:

Holography is a tool that can be most readily applied to studies of transport properties in gauge theories with infinitely strong interactions. Coupling constant corrections can then be incorporated through higher-derivative (alpha-prime) corrections to the supergravity action in the bulk. In the first part of this talk, I will discuss the dependence of higher-order hydrodynamic transport (beyond Navier-Stokes) and the higher-frequency (quasi-normal) spectrum on the coupling constant in duals of Type IIB supergravity and curvature-squared theories. In relation to the membrane paradigm, I will then present higher-order generalisations of the universal "eta over s" relation and universal anomalous conductivities at finite coupling. Recently, studies of holographic transport in the presence of broken translational symmetry and disorder have received much attention. In particular, it has been shown how thermo-electric conductivities can be computed by using the membrane paradigm. Through the power of the membrane paradigm and with a view towards future models of many-body localisation without hydrodynamic transport, in the second part of this talk, I will discuss the proofs of the lower bounds on thermal and electrical conductivities in a large family of holographic theories with arbitrarily strong disorder.

08.02.2016 (Monday)

Partition Functions in Even Dimensional AdS via Quasinormal Mode Methods

Exceptional Seminar Cindy Keeler (NBI)

at:
14:00 IC
room H503
abstract:

After a review of the quasinormal mode method for partition function calculation developed by Denef, Hartnoll, and Sachdev, we study a scalar in AdS2. We find a series of zero modes with negative real values of the conformal dimension whose presence indicates a series of poles in the one-loop partition function. The contribution of these poles to the AdS partition function at physical mass values matches previous results. Additionally, extending our results to AdS in any even dimension 2n, we find a similar series of zero modes related to discrete series representations of SO(2n,1), and successfully calculate the one-loop determinant from these modes. Finally, we speculate on the physical meaning of these non-physical-mass modes.

28.01.2016 (Thursday)

One loop partition function of six dimensional conformal gravity using heat kernel on AdS_2n

Regular Seminar Iva Lovrekovic (Vienna)

at:
13:30 IC
room H503
abstract:

We compute the heat kernel for the Laplacians of symmetric transverse traceless fields of arbitrary spin on the AdS background in even number of dimensions using the group theoretic approach and apply it on the partition function of six dimensional conformal gravity. The obtained partition function consists of the Einstein gravity, conformal ghost, partially massless mode and massive mode.

20.01.2016 (Wednesday)

Polygon Seminar: SUSY field theories and matrix models

Triangular Seminar Nadav Drukker (KCL)

at:
15:00 IC
room LT3 Level 1 Blackett
abstract:

Matrix models are toy models for quantum field theories. They can be extremely complicated but can also be solved in a variety of ways. In my talk I will discuss general properties of matrix models and their solutions and focus on particular matrix models that arise in the study of 4d SUSY field theories. Those matrix models describe the index of the field theory, counting the number of states of the theory (with + sign for a boson and - for a fermion) and have been known for over 10 years. Though they look very complicated I will show how some simple tricks allow in certain cases to solve those matrix models exactly in terms of elementary functions. My talk will focus on the matrix model calculation and no specialized knowledge of SUSY field theories or indices would be required to follow it.

13.01.2016 (Wednesday)

Negativities, entanglement structures of qubit systems and holography

Regular Seminar Massimiliano Rota (Durham)

at:
14:00 IC
room H503
abstract:

Entanglement entropy is a very important quantity in holography, nevertheless it is only a measure of the total amount of entanglement between two complementary subsystems in a global pure state. A more detailed knowledge about the pattern of entanglement is essential for a deeper understanding of the relation between bulk geometry and quantum information in the boundary theory. I will discuss how negativities and other measures can be used in this context focusing in particular on qubit systems for which a classification of possible entanglement structures is available.

16.12.2015 (Wednesday)

Effective theories of thermoelectric transport from holography

Regular Seminar Blaise Gouteraux (Stanford)

at:
14:00 IC
room H503
abstract:

In this talk, I will summarize recent progress in the description of thermoelectric transport using gauge/gravity duality. I will first review thermoelectric transport in hydrodynamics, where momentum conservation implies infinite zero-frequency conductivities. By a change of basis of the conserved currents, a universal, finite conductivity can be extracted. It can be computed holographically. I will discuss its low-temperature scaling in terms of critical exponents characterizing time and space anisotropy and anomalous dimensions for the free energy and conserved current. When momentum is almost conserved, the zero-frequency delta functions broaden into Drude-like peaks. A holographic computation precisely identifies the redistribution of the low-frequency spectral weight between two contributions originating from the non-conservation of momentum and intrinsic dissipation respectively. It also sheds some light on how to construct effective theories of thermoelectric transport when momentum is not conserved.

09.12.2015 (Wednesday)

Holographic thermo-electric transport properties and strange metals

Regular Seminar Andrea Amoretti (Cambridge)

at:
14:00 IC
room H503
abstract:

Gauge/gravity duality can be used to study the transport properties of strongly interacting systems with no quasi-particles. I will give an overview of some holographic toy models of states like this, in which momentum is not conserved and thus the transport of energy and charge is non-trivial. Specifically I will discuss the thermoelectric transport properties of these toy models and their possible relations to the phenomenology of the strange metals.

25.11.2015 (Wednesday)

Solving the Scattering Equations

Regular Seminar Peter Goddard (IAS)

at:
14:00 IC
room H503
abstract:

Describing work in collaboration with Louise Dolan, I will discuss the scattering equations, originally introduced in 1972 by Fairlie and Roberts searching for new dual models, rediscovered by Gross and Mende in 1988, discussing the high energy behaviour of string theory, and more recently shown by Cachazo, He and Yuan to provide a kinematic basis for describing remarkable formulae for tree amplitudes for massless particles in arbitrary space-time dimension (including scalars, gauge bosons and gravitons). We reformulate the scattering equations for N particles as a system of N -3 homogeneous polynomial equations in N - 2 complex variables, which are linear in each variable separately. The linearity of the equations enables their explicit solution in terms of the roots of a single-variable polynomial of degree (N-3)!, which can itself be explicitly constructed in terms of the Mandelstam variables formed from the momenta. The possible extension to one loop and the special case of four-dimensional space-time will also be briefly discussed.

11.11.2015 (Wednesday)

Exact Results for Entanglement and Renyi Entropies, and their Gravity Duals

Regular Seminar Julian Sonner (University of Geneva)

at:
14:30 IC
room H503
abstract:

The recent focus on entanglement entropy in holography has many motivations, ranging from the applied (e.g. AdS/CMT) to the foundational (emergence of gravity). For all of these programs It is important to find examples, where the quantities of interest can be directly calculated in strongly-coupled field theories and, moreover, the dual geometry constructed at strong coupling. In this talk I will describe joint work with Crossley and Dyer on using localization methods to obtain entanglement and (super-) Renyi entropies of the N=4 SYM theory with gauge group SU(N) in 4D at all values of the ít Hooft coupling \lambda and number of colors N. Since obtaining quantities like entanglement and Renyi entropies involves working on singular spaces, which typically break the supersymmetry, we focus on a supersymmetric generalization, the so-called super-Renyi entropy where the supersymmetry breaking effects of the singularities are suitably compensated. I will also discuss dual gravity solutions as five-dimensional BPS black holes with hyperbolic horizon. I will conclude with a description of Wilson loops, that is the contribution to the entanglement and Renyi entropies due to adding fundamental matter to the theory.

04.11.2015 (Wednesday)

Thermalization in 2d CFTs revisited

Triangular Seminar Jan de Boer (Amsterdam U.)

at:
15:00 IC
room LT1
abstract:

While a lot of work has been done on understanding thermalization in 2d CFTs, several confusing aspects remain, in particular regarding integrable aspects of 2d CFTs. In this talk I will try to summarize some of these confusions and how these connect to AdS/CFT and black hole formation. There appears to be a significant difference between thermalization in low c CFTs versus thermalization in large c CFTs with gravitational duals.

04.11.2015 (Wednesday)

Black holes, Stokes flows and DC transport at strong coupling

Triangular Seminar Aristomenis Donos (Durham U.)

at:
16:30 IC
room LT1
abstract:

Certain materials, such as the cuprate superconductors and heavy fermion materials exhibit fascinating, yet hard to explain transport properties. Holography provides a consistent framework to examine linear response and in particular transport of strongly coupled matter. I will discuss momentum dissipation in holography and show that DC transport is fixed via a Stokes flow of an "auxiliary fluid" residing on the horizon of black holes.

28.10.2015 (Wednesday)

Knots in 3d-3d Correspondence

Regular Seminar Masahito Yamazaki (Kavli IPMU)

at:
14:00 IC
room H503
abstract:

I will discuss knot-like defects in CS theory with complex gauge group SL(N), in the context of its connection with 3d N=2 theory (the so-called 3d-3d correspondence). I am hoping to discuss this problem from a number of different perspectives, including cluster algebras, state-integral models, 3d N=2 non-Abelian gauge theories, 5d N=2 SYM, and holographic dual, and discuss the consistency checks as well as new predictions/implications. This talk is mostly based on my recent papers with D. Gang, N. Kim and M. Romo.

22.10.2015 (Thursday)

T-Self Duality of AdS(d) x S(d) x S(d) Superstrings

Exceptional Seminar Antonio Pittelli (Surrey University)

at:
13:30 IC
room H503
abstract:

Dual superconformal symmetry is a remarkable, hidden feature of N=4 SYM in 4 dimensions. Via AdS/CFT, such a symmetry corresponds to the invariance of the AdS(5) x S(5) superstring under specific combinations of bosonic and fermionic T-dualities. We show that AdS(d) x S(d) x S(d) superstrings with D(2,1;\alpha) isometry supergroup are T-self-dual if additional T-dualities along complexified S(d) directions are performed. This implies that CFTs dual to AdS(d) x S(d) x S(d) x T(10-3d) superstrings enjoy a new type of dual superconformal symmetry.

15.10.2015 (Thursday)

Interactions in Vasiliev's Theory, Holography and Locality

Exceptional Seminar Massimo Taronna (AEI)

at:
13:30 IC
room H503
abstract:

The aim of this talk is to extract the quadratic corrections to Fronsdal equations from Vasiliev's equations, and discuss their structure. The issue of locality in higher-spin theories will be addressed. Implications of this analysis in relation to Giombi-Yin checks of higher-spin/vector model duality will be discussed. Some of the previous puzzles will be resolved, while others will be elucidated.

14.10.2015 (Wednesday)

All order alpha' corrections to BPS,non-BPS and brane anti-brane effective actions of type IIA,IIB superstring theory

Regular Seminar Ehsan Hatefi (Queen Mary)

at:
14:00 IC
room H503
abstract:

We would like to talk about all kinds of supersymmetric and non-supersymmetric scattering amplitudes of type IIA,IIB superstring theory as well as their corrections. In fact we want to address how to get to a universal conjecture for DBI, Chern-Simons and more importantly new Wess Zumino actions with their all order $\alpha'$ corrections. Indeed we try to provide a comprehensive explanation even for D- brane-anti D-brane systems, where various new techniques will be also introduced. If time allows , we then mention several issues related to those effective actions and eventually highlight some comments about higher point functions of the Mixed closed string RR , scalar fields in different pictures of the string theory amplitude.

08.10.2015 (Thursday)

All gaugings and stable de Sitter in D=7 half-maximal supergravity

Regular Seminar Jose Fernandez-Melgarejo (Harvard)

at:
13:30 IC
room H503
abstract:

We study the general formulation of gauged supergravity in seven dimensions with sixteen supercharges keeping duality covariance by means of the embedding tensor formalism. We first classify all inequivalent duality orbits of consistent deformations. Secondly, we analyse the complete set of critical points in a systematic way. Interestingly, we find the first examples of stable de Sitter solutions within a theory with such a large amount of supersymmetry.

29.07.2015 (Wednesday)

Connections on Courant Algebroids

Regular Seminar Branislav Jurco (Charles University/MPIM)

at:
14:00 IC
room H503
abstract:

We introduce connection, torsion and curvature for Courant algebroids. We discuss in detail torsionless connections compatible with a generalized metric and the related Einstein-Hilbert actions.

01.07.2015 (Wednesday)

Localization in Quiver Quantum Mechanics

Regular Seminar Kazutoshi Ohta (Meiji Gakuin University)

at:
13:00 IC
room H503
abstract:

We derive the localization formula for N=4 supersymmetric quiver quantum mechanics in the Higgs and Coulomb branch. The partition function (index) is exactly evaluated and it is shown that the path integral is localized at fixed points, which are given by solutions to the BRST equations combined with D-term and F-term conditions. We give various examples of the quiver theory and classifications of their fixed points. The indexes completely agree with the mathematical wall crossing formulae for the quiver moduli spaces. We also discuss a gravitational picture of the localization in the Coulomb branch.

24.06.2015 (Wednesday)

Defects and quantum Seiberg-Witten geometry

Regular Seminar Peter Koroteev (PI)

at:
14:00 IC
room H503
abstract:

23.06.2015 (Tuesday)

Strings of 6d SCFTs

Regular Seminar Babak Haghighat (Harvard)

at:
13:30 IC
room H503
abstract:

We consider bound states of strings which arise in 6d (1,0) SCFTs that are realized in F-theory in terms of linear chains of spheres with negative self-intersections 1,2, and 4. These include the strings associated to N small E8 instantons, as well as the ones associated to M5 branes probing A and D type singularities in M-theory or D5 branes probing ADE singularities in Type IIB string theory. We find that these bound states of strings admit (0,4) supersymmetric quiver descriptions and show how one can compute their elliptic genera.