## Directions

We are located on the Main Campus of City in Northampton Square (map)

Getting to the Strand Campus:

• #### By underground

Thea nearest tube stops are Farringdon, Angel, also nearby is Barbican

• #### By train

Farringdon (10 minutes walk) or King's Cross stations (20 minutes walk) have nearest main-line services

• #### By bus

Buses stopping outside the College: : 4, 19, 30, 38, 43, 55, 56, 63, 73, 153, 205, 214, 243, 274, 341, 394, 476.

## Seminars at City, University of London

Found at least 20 result(s)

### 20.11.2019 (Wednesday)

#### 5d Gauge Theories, SCFTs and Dualities

Polygon Seminar Sakura Schafer-Nameki (Oxford)

 at: 15:00 City U.room B104 abstract: I will discuss recent developments in constructions of 5d N=1 supersymmetric gauge theories and their UV fixed points, which are strongly-coupled SCFTs. The lectures will start with some background on 5d gauge theories, their Coulomb branch and effective action, as well as their constructions in M-theory on non-compact Calabi-Yau threefolds. In the second lecture I will discuss some new developments of various groups in the past year.

### 19.11.2019 (Tuesday)

#### Making sense of a non-Hermitian Lagrangian in Field Theory

Regular Seminar Jean Alexandre (King's)

 at: 15:00 City U.room B104 abstract: Motivated by extending the parameter space of the Standard Model of Particle Physics, I will describe how to understand the effects of an imaginary mixing mass term in a non-Hermitian but PT-symmetric extension of scalar QED. The classical theory is already not trivial, and requires a new interpretation of the equations of motion, Noether's theorem and gauge invariance. The path integral can be defined with appropriate field variables, and a consistent picture emerges, opening the way for potential alternative descriptions of the Higgs sector.

### 12.11.2019 (Tuesday)

#### TBA

Regular Seminar Misha Feigin (Glasgow)

 at: 15:00 City U.room C300 abstract:

### 05.11.2019 (Tuesday)

#### TBA

Regular Seminar Klaus Ritzberger (Royal Holloway)

 at: 15:00 City U.room C300 abstract:

### 22.10.2019 (Tuesday)

#### TBA

Regular Seminar Bernd Braunecker (St. Andrews)

 at: 15:00 City U.room B104 abstract:

### 15.10.2019 (Tuesday)

#### TBA

Regular Seminar Fabian Ruhle (CERN)

 at: 15:00 City U.room C310 abstract:

### 08.10.2019 (Tuesday)

#### The isolated Heisenberg magnet as a quantum time crystal

Regular Seminar Marko Medenjak (ENS)

 at: 15:00 City U.room C316 abstract: Isolated systems consisting of many interacting particles are generally assumed to relax to a stationary equilibrium state whose macroscopic properties are described by the laws of thermodynamics and statistical physics. Time crystals, as first proposed by Wilczek, could defy some of these fundamental laws and for instance display persistent non-decaying oscillations. They can be engineered by external driving or contact with an environment, but are believed to be impossible to realize in isolated many-body systems. I will show that the paradigmatic model of quantum magnetism, the Heisenberg XXZ spin chain, does not relax to stationarity and hence constitutes a genuine time crystal that does not rely on external driving or coupling to an environment. I will trace this phenomenon to the existence of periodic extensive quantities and find their frequency to be a no-where continuous (fractal) function of the anisotropy parameter of the chain.

### 01.10.2019 (Tuesday)

#### Symmetry breaking in non-Hermitian, PT-symmetric quantum field theories

Regular Seminar Peter Millington (Nottingham)

 at: 15:00 City U.room ELG02 abstract: We consider the continuous symmetry properties of non-Hermitian, PT-symmetric quantum field theories. We begin by revisiting the derivation of Noetherâ€™s theorem and find that the conserved currents of non-Hermitian theories correspond to transformations that do not leave the Lagrangian invariant. After describing the implications of this conclusion for gauge invariance, we consider the spontaneous breakdown of global and local symmetries, and illustrate how the Goldstone theorem and the Englert-Brout-Higgs mechanism are borne out. We conclude by commenting on the potential avenues for model building in fundamental physics from the non-Hermitian deformation of the Standard Model of particle physics.

### 10.06.2019 (Monday)

#### Conformal block, Crossing Kernel and Multi-variable Hypergeometric Functions

Regular Seminar Heng-Yu Chen (National Taiwan University)

 at: 11:00 City U.room E205 abstract: In this talk, based on the work to appear, we present an alternative representation of the conformal block with external scalars in general spacetime dimensions in terms of a finite summation over Appell fourth hypergeometric function, and its generalization to the primary operator exchange with continuous spin which is relevant for Lorentzian spacetime. Using these results we apply the Lorentzian inversion formula to compute so-called crossing kernel in general spacetime dimensions, and the result can be written as a double infinite summation over certain Kempe de Feriet hypergeometric functions. During the talk, we will introduce various physical quantities and discuss their subtitles and applications.

### 02.04.2019 (Tuesday)

#### Tensionless Strings and Quantum Gravity Conjectures

Regular Seminar Seung-Joo Lee (CERN)

 at: 15:00 City U.room C309 abstract: We test various conjectures on quantum gravity with general 6d string compactifications in the framework of F-theory. Starting with a gauge theory coupled to gravity, we first analyze the limit in KÃ¤hler moduli space where the gauge coupling tends to zero while gravity is kept dynamical. A key observation is made about the appearance of a tensionless string in such a limit. For a more quantitative analysis, we focus on a U(1) gauge symmetry and determine the elliptic genus of this string in terms of certain meromorphic weak Jacobi forms, of which modular properties allow us to determine the charge-to-mass ratios of certain string excitations. A tower of these asymptotically massless charged states are then confirmed to satisfy the (sub-)Lattice Weak Gravity Conjecture, the Completeness Conjecture, and the Swampland Distance Conjecture. We interpret their charge-to-mass ratios in two a priori independent perspectives. All of this is then generalized to theories with multiple U(1)s. If time permits, we will also briefly report on our more recent 4-dimensional story.

### 25.03.2019 (Monday)

#### TBA

Regular Seminar Sat Gupta (UNC)

 at: 15:00 City U.room C318 abstract:

### 20.03.2019 (Wednesday)

#### Scattering amplitudes and their applications

Polygon Seminar Congkao Wen (QMUL)

 at: 15:00 City U.room A130 abstract: Scattering amplitudes are one of most important class of physical observables in quantum field theories. Over the last decade or so, there has been a lot of activities regarding the computation of scattering amplitudes in a wide range of interesting theories, where extremely powerful new frameworks for studying scattering amplitudes have emerged, known as the modern S-matrix program. In this talk I will review some of these powerful techniques, and discuss their applications. The applications will mostly focus on effective field theories, that include twistor-like formulas for scattering amplitudes of world-volume theories of probe D-brane and M5 brane, amplitude constraints on effective field theories, such as supersymmetric non-renormalization theorems, unitarity bounds on low-energy spectra.

### 19.03.2019 (Tuesday)

#### TBA

Regular Seminar Misha Portnoi (Exeter)

 at: 15:00 City U.room AG22 abstract:

### 12.03.2019 (Tuesday)

#### TBA

 at: 15:00 City U.room C320 abstract:

### 05.03.2019 (Tuesday)

#### TBA

Regular Seminar Weini Huang (QMUL)

 at: 15:00 City U.room C309 abstract:

### 19.02.2019 (Tuesday)

#### From Yang-Mills and Maxwell in de Sitter space electromagnetic knots

Regular Seminar Olaf Lechtenfeld (Hannover)

 at: 15:00 City U.room AG21 abstract: I will review analytic SU(2) Yang-Mills solutions with finite action on de Sitter space from a new perspective. As a byproduct, all abelian solutions are classified and related with rational electromagnetic knots. In the Yang-Mills case, the gravitational backreaction is easily taken in to account as well.

### 12.02.2019 (Tuesday)

#### TBA

 at: 15:00 City U.room C305 abstract:

### 06.02.2019 (Wednesday)

#### TBA

Triangular Seminar Eliezer Rabinovici (HUJ)

 at: 15:00 City U.room BG03 abstract:

### 06.02.2019 (Wednesday)

#### A Worldsheet Dual for the Symmetric Orbifold

Triangular Seminar Rajesh Gopakumar (ICTS-TIFR)

 at: 16:30 City U.room BG03 abstract: We will argue that superstring theory on ${\rm AdS}_3\times {\rm S}^3\times \mathbb{T}^4$ with the smallest amount of NS-NS flux ($k=1$'') is dual to the spacetime CFT given by the large $N$ limit of the free symmetric product orbifold $\mathrm{Sym}^N(\mathbb{T}^4)$. The worldsheet theory, at $k=1$, is defined using the hybrid formalism in which the ${\rm AdS}_3\times {\rm S}^3$ part is described by a $\mathfrak{psu}(1,1|2)_1$ WZW model (which is well defined). Unlike the case for $k\geq 2$, it turns out that the string spectrum at $k=1$ does not exhibit a long string continuum, and perfectly matches with the large $N$ limit of the symmetric product. The fusion rules of the symmetric orbifold are also reproduced from the worldsheet perspective. This proposal therefore affords a tractable worldsheet description of a tensionless limit in string theory.

### 05.02.2019 (Tuesday)

#### Mode interactions in complex and disordered patterns

Regular Seminar Alastair Rucklidge (Leeds)

 at: 15:00 City U.room BLG07 abstract: Why do some systems organise themselves into well ordered patterns with astonishing symmetry and regularity, while other superficially similar systems produce defects and disorder? In systems where two different length scales are unstable, the nonlinear interaction between the different modes is key: steady complex patterns can be stabilised when the modes act together to reinforce each other. But, if the two types of pattern compete with each other, the outcome can be considerably more complicated: a time-dependent disordered mixture of patterns constantly shifting and changing. In a small domain, the nature of the interaction between a small number of modes on each length scale can readily be computed. In a large domain, each mode can interact with hundreds of other modes, but the overall behaviour still appears to be guided by small-domain considerations.