## 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)

### 26.09.2018 (Wednesday)

#### Amplitudes and hidden symmetries in supersymmetric Chern-Simons matter theories

Regular Seminar Karthik Inbasekar (Tel Aviv University)

 at: 14:00 ICroom H503 abstract: Chern-Simons theories coupled to fundamental matter have a wide variety of applications ranging from Quantum Hall effect to Quantum gravity via AdS/CFT. These theories enjoy a strong weak duality that has been tested to a very good accuracy via large N computations, such as thermal partition functions, and S matrices. Supersymmetric Chern-Simons theories are equally interesting since they have a self duality and relate to non-supersymmetric theories via RG flows. In the N=2,3 supersymmetric Chern-Simons matter theories, the four point amplitude computed to all orders in the 't Hooft coupling is not renormalised! It is a unique situation in a quantum field theory that the scattering amplitude doesn't receive loop corrections. This indicates the presence of powerful symmetry structures within the theory. This also suggests that higher point amplitudes may be easier to compute using four point amplitudes as building blocks. These higher point amplitudes not only serve as a testing tool for duality but also a probe into the symmetry structure of the theory. As a first step towards this goal, we begin by computing arbitrary n point tree level amplitudes in the N=2 theory via BCFW recursion relations. We then show that the four point tree level amplitude enjoys a dual superconformal symmetry. Since the all loop four point amplitude is tree level exact, it follows that the dual superconformal symmetry is exact to all loops. This is in contrast to highly supersymmetric examples such as N=4 SYM and N=6 ABJM, where the dual superconformal symmetry is in general anomalous. Furthermore, we show that the superconformal and dual superconformal symmetries generate an infinite dimensional Yangian symmetry for the four point amplitude. If these symmetries persist to higher point amplitudes, this suggests that the N=2 superconformal Chern-Simons matter theory may be integrable.

### 02.05.2018 (Wednesday)

#### Losing the IR: A New Framework for Holographic Area Laws

Regular Seminar Netta Engelhardt (Princeton)

 at: 14:00 ICroom H503 abstract: I will describe a new procedure for coarse-graining over the gravitational degrees of freedom inside a surface in the context of AdS/CFT. I will prove that in general dimensions, this coarse-graining gives an explanation of an infinite family of gravitational area laws. In three bulk dimensions, it is also straightforward to derive the precise dual of these area laws as strong subadditivity of the von Neuman entropy in the dual CFT. I will discuss a number of implications of this, which include an explanation for the geometric bulk phenomenon of extremal surface barriers

### 21.02.2018 (Wednesday)

#### Polygon Seminar

Triangular Seminar Kostas Skenderis and Andrei Starinets (Southampton, Oxford)

 at: 15:00 ICroom Blackett LT2 abstract: Kostas Skenderis: Title: "Towards a general AdS/Ricci-flat correspondence" Abstract: The AdS/Ricci-flat (AdS/RF) correspondence is a map between families of asymptotically locally AdS solutions on a torus and families of asymptotically flat spacetimes on a sphere. In this talk I will discuss how to relax these restrictions for linearized perturbations around solutions connected via the original AdS/RF correspondence. This correspondence should allow us to develop a detailed holographic dictionary for asymptotically flat spacetimes. Andrei Starinets: TBA

### 19.02.2018 (Monday)

#### All-point correlation functions in SYK

 at: 14:00 ICroom H503 abstract: We discuss the computation of all-point correlation functions in the SYK model, at leading order in 1/N. The result has remarkable simplicity and structure. The result is general, holding for any theory in which one forms higher-point correlators by gluing together four-point functions; for instance, large N vector models and tensor models. It implies specific singularity structure of analytically extended OPE coefficients. In particular, the analytically extended OPE coefficients of the single-trace operators encode the OPE coefficients of the double-trace operators

### 08.02.2018 (Thursday)

#### Holographic Effective Field Theories for Charge Density Wave States

Exceptional Seminar Daniele Musso (IGFAE)

 at: 13:00 ICroom H503 abstract: The spatially modulated self-organization of strongly-correlated electrons is central in describing the phenomenology of many condensed matter systems, such as the cuprates and the manganites. Holography can describe spontaneous formation of various kinds of density waves in a strongly-coupled media and provides toy-model effective field theories able to capture important phenomenological features, such as the low-temperature scaling of the conductivity. Appropriate UV completions of the holographic EFT can also describe the spontaneous generation of the spatial features themselves.

### 06.12.2017 (Wednesday)

#### Holographic Phonons

Regular Seminar Matteo Baggioli (University of Crete)

 at: 13:00 ICroom H503 abstract: We discuss the presence of phonons and the interplay between spontaneous and explicit breaking of translations in the context of holography. Using two different bottom-up models we show the existence of transverse and longitudinal phonons, whose properties are in perfect agreement with elastic theory and hydrodynamics. We focus our attention on the elastic and transport features of the dual QFT also in the presence of a small explicit breaking. We conclude speculating about the possibility of having gravitational duals for strongly coupled viscoelastic materials.

### 29.11.2017 (Wednesday)

#### RG flows in 3d N=4 gauge theories

Regular Seminar Benjamin Assel (CERN)

 at: 14:00 ICroom H503 abstract: I will present a new approach to study the RG flow in 3d N=4 gauge theories, based on an analysis of the Coulomb branch of vacua. The Coulomb branch is described as a complex algebraic variety and important information about the strongly coupled fixed points of the theory can be extracted from the study of its singularities. I will use this framework to study the fixed points of USp(2N) gauge theories with fundamental matter, revealing some surprising features at low amount of matter.

### 08.11.2017 (Wednesday)

#### RG Flows Across Dimensions and Holography

Regular Seminar Nikolay Bobev (KU Leuven)

 at: 14:00 ICroom H503 abstract: Superconformal field theories placed in nontrivial background fields for the metric and the continuous global symmetries exhibit a rich web of RG flows across dimensions. I will discuss several examples of such flows and emphasize some of their universal features. In addition, I will employ non-perturbative tools such as 't Hooft anomaly matching, a-, F-, and c-extremization, and holography to gain a quantitative understanding of some aspects of these theories. Finally, I will discuss the relevance of these results for a microscopic understanding of the entropy of supersymmetric black holes and strings in AdS.

### 01.11.2017 (Wednesday)

#### Triangle Seminar: The S-matrix bootstrap - old and new

Triangular Seminar Balt Van Rees ()

 at: 15:00 ICroom LT2 abstract: From a modern viewpoint the "S-matrix bootstrap" is the idea that general consistency conditions can be used to obtain quantitative constraints on scattering amplitudes. I will discuss the assumptions behind this approach, open questions about the structure of amplitudes, and discuss some fundamental results from the sixties and seventies. In the second part of the talk I will treat two modern approaches which were inspired by recent results on the conformal bootstrap, and show how they can be used to constrain scattering amplitudes in non-trivial ways.

### 25.10.2017 (Wednesday)

#### Current Algebra and CFTs at Null Infinity from Amplitudes

Regular Seminar Dhritiman Nandan (Edinburgh)

 at: 14:00 ICroom H503 abstract: We describe the leading and sub-leading multi-soft behavior of tree level gluon amplitudes and an underlying two-dimensional description of such scenarios where the soft limits are currents related to asymptotic symmetries of YM theory. Such kinematic limits allow us to explore the algebra of these two dimensional currents and we comment on their CFT interpretation. Then we explore a possible two-dimensional description of certain amplitudes in massive scalar QFT’s.

### 04.10.2017 (Wednesday)

#### TBA

Regular Seminar Nabil Iqbal (Durham)

 at: 14:00 ICroom H503 abstract:

### 27.09.2017 (Wednesday)

#### TBA

Regular Seminar Antoine Bourget (Oviedo)

 at: 14:00 ICroom H711C abstract:

### 20.09.2017 (Wednesday)

#### Alternative boundary conditions in AdS, one-loop determinants and WCFTs

Regular Seminar Phil Szepietowski (Utrecht)

 at: 14:00 ICroom Elec. Eng. 509A abstract: I will discuss the computation of the graviton one-loop determinant in the BTZ black hole background with certain chiral boundary conditions at the AdS boundary. These boundary conditions were proposed by Compere, Song and Strominger and were shown to modify the asymptotic symmetry algebra from a sum of left and right Virasoro algebras to a single right-moving Virasoro U(1) Kac-Moody. This implies that the holographic dual description possesses such global symmetry and so should be described by a warped conformal field theory (WCFT) instead of a standard CFT. In the talk I will overview the new boundary conditions and the concept of a WCFT, outline the computational method of obtaining the one-loop determinant from the "quasinormal" mode spectrum (highlighting elements which are unique to the new boundary conditions) and discuss the implications of the results for the boundary field theory.

### 14.09.2017 (Thursday)

#### The decay width of stringy hadrons

Exceptional Seminar Jacob Sonnenschein (Tel Aviv University)

 at: 14:00 ICroom H503 abstract: I will start with briefly describing the HISH ( Holography In- spired Hadronic String) model and reviewing the fits of the spectra of mesons, baryons, glueballs and exotic hadrons. I will present the determination of the hadron strong decay widths. The main decay mechanism is that of a string splitting into two strings. The corresponding total decay width behaves as Γ = πATL/2 where T and L are the tension and length of the string and A is a dimensionless universal constant. The partial width of a given decay mode is given by Γ_i/Γ = Φ_i exp(−2πCm^2_sep/T) where Φi is a phase space factor, msep is the mass of the ”quark” and ”antiquark” created at the splitting point, and C is a dimensionless coefficient close to unity. I will show the fits of the theoretical results to experimental data for mesons and baryons. I will examine both the linearity in L and the expo- nential suppression factor. The linearity was found to agree with the data well for mesons but less for baryons. The extracted coefficient for mesons A = 0.095 ± 0.015 is indeed quite universal. The exponential suppression was applied to both strong and radiative decays. I will discuss the relation with string fragmentation and jet formation. I will extract the quark-diquark structure of baryons from their decays. A stringy mechanism for Zweig sup- pressed decays of quarkonia will be proposed and will be shown to reproduce the decay width of Υ states. The dependence of the width on spin and flavor symmetry will be discussed. We further apply this model to the decays of glueballs and exotic hadrons.

### 13.09.2017 (Wednesday)

#### Higher-loop amplitude monodromy relations in string and gauge theory

Regular Seminar Piotr Tourkine (DAMTP)

 at: 14:00 ICroom H503 abstract: The monodromy relations of scattering amplitudes in string theory provide an elegant formalism to understand some mysterious properties of tree-level field theory amplitudes, like the color-kinematics duality. This duality has been instrumental in tremendous progress on the computations of loop-amplitudes in quantum field theory, but a loop-level generalisation of the stringy monodromy construction has been lacking for many years. In this talk I will first describe some of these recent developments in the domain of scattering amplitudes in gauge and gravity theories. I’ll then review the monodromies of open string worldsheets and how the lead at tree-level to deepening the understanding of the gauge theory perturbative expansion. Then I will describe in a non-technical manner our results and how we managed to extend these relations to all loops in string and field theory. I’ll finish by discussing implications for the loop expansion in general, and how to extend in principle these results to gravity. I will assume no prior knowledge of the audience in modern scattering amplitudes methods.

### 26.05.2017 (Friday)

#### Goldstino superfields in supergravity

Exceptional Seminar Sergei Kuzenko (U Western Australia)

 at: 15:00 ICroom H503 abstract: Models with spontaneously broken local supersymmetry are naturally obtained by coupling the off-shell supergravity-matter systems to Goldstino superfields. Every irreducible Goldstino superfield produces a universal positive contribution to the cosmological constant. This talk will review the structure of N=1 and N=2 Goldstino superfields.

### 24.05.2017 (Wednesday)

#### Diffusion and Chaos in Holographic Matter

Regular Seminar Mike Blake (MIT)

 at: 14:00 ICroom H503 abstract: In this talk I will discuss recent developments that have suggested new connections between the transport properties of strongly interacting matter and the field of quantum chaos. In particular I will describe how in many holographic theories there are simple relationships between the thermoelectric diffusion constants and the butterfly velocity, which describes the speed at which quantum chaos propagates.

### 22.05.2017 (Monday)

#### An introduction to Gauge Theory in Superspace

Exceptional Seminar Rikard von Unge (Masaryk University)

 at: 14:00 ICroom B1004 abstract: TBA

### 18.05.2017 (Thursday)

#### Double field theory and doubled geometry

Regular Seminar Chris Blair (Vrije U., Brussels)

 at: 13:00 ICroom H503 abstract: I will discuss some aspects of the doubled geometry of double field theory. Double field theory provides a reformulation of supergravity with a manifest O(D,D) symmetry, which can be related to the T-duality invariance of string theory on a torus. I will review how one achieves this, by doubling the number of coordinates and introducing a generalised diffeomorphism symmetry. Then, I will discuss how one can characterise the properties of string theory backgrounds viewed as solutions of DFT, and in particular show how to derive the first law of black hole thermodynamics in this framework. Based mainly on 1507.07541 and 1608.04734 (with Alex Arvanitakis).

### 10.05.2017 (Wednesday)

#### M-theory on deformed Sasaki-Einstein manifolds

Regular Seminar Stefanos Katmadas (IPhT, Saclay)

 at: 14:00 ICroom H503 abstract: Compactifications of M-theory down to AdS4 are known to arise from Sasaki-Einstein internal spaces. The latter can be viewed as surfaces enclosing Calabi-Yau cone singularities, whose deformations can be described algebraically in a well established way. In this talk, I will present work in progress on describing deformations of the enclosing surfaces away from the Sasaki-Einstein metric, using the deformations of the Calabi-Yau cone. This provides a realisation of a class of SU(3) structure manifolds satisfying the conditions postulated in the standard treatments of M-theory compactifications on such manifolds. The result is a proposal for obtaining four dimensional N=2 supergravity models with gauged hypermultiplets from deformations of regular Sasaki-Einstein manifolds.