## 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)

### 24.01.2012 (Tuesday)

#### Ricci solitons

Regular Seminar Andrew Dancer (Oxford)

 at: 16:00 City U.room CG04 abstract: A Ricci soliton is a generalisation of an Einstein metric which evolves in a very simple way under the Ricci flow. We discuss ways of producing examples of Ricci solitons by looking for solutions with a high degree of symmetry

### 25.10.2011 (Tuesday)

#### Instantons, Integrability and N=2 SUSY: The Basics

Regular Seminar Tim Hollowood (Swansea)

 at: 16:00 City U.room CG02 abstract: This talk will give a pedagogical account of the role played by integrability and instantons in N=2 SUSY gauge theories leading to recent understanding of what it means to quantize the integrable system.

### 19.10.2011 (Wednesday)

#### Dimer Models, Integrable Systems and Gauge Theory

Triangular Seminar Sebastian Franco (Durham)

 at: 17:00 City U.room A130, College building abstract: Dimer models are typically studied in condesed matter physics and combinatorics. The correspondence between dimer models, toric Calabi-Yaus and quiver gauge theories on D-branes has had a profound impact in areas ranging from string phenomenology to mathematics. Today I will discuss a recently discovered correspondence between dimer models and integrable systems.

### 19.10.2011 (Wednesday)

#### Super Yang-Mills Amplitudes in Flatland

Triangular Seminar Donovan Young (NBI)

 at: 15:30 City U.room A130, College building abstract: I will discuss scattering amplitudes in N=2,4,8 SYM in three-dimensions, concentrating on the N=8 case, with an emphasis on which properties of the N=4, D=4 SYM amplitudes survive under dimensional reduction. The on-shell supersymmetry algebra makes the SO(N) symmetry of the amplitudes manifest, while the Lagrangian displays only manifest SO(N-1) symmetry. I will also discuss the possibility of non-local Yangian-type symmetry, connections to BLG, and some perspectives on loop level results. Based on 1103.0786 / 1109.2792.

### 18.10.2011 (Tuesday)

#### Permutations, Strings and Feynman Graphs

Regular Seminar Sanjaye Ramgoolam (QMUL)

 at: 16:00 City U.room CG02 abstract: Abstract : Feynman Graph counting in Quantum Field Theory (QFT) can be formulated in terms of symmetric groups. This leads to expressions for graph counting and symmetry factors in terms of topological transition amplitudes for strings with a cylinder target, related to two dimensional topological field theory. The details of the interactions in the QFT are encoded in the boundary conditions which specify how the strings wind around circles. The QFTs discussed include scalar field theories and QED, where there is no large gauge group.

### 11.10.2011 (Tuesday)

#### Forcing, independence, Plato and multiuniverses of set theory

Regular Seminar Mirna Dzamonja (University of East Anglia)

 at: 16:00 City U.room CG02 abstract: We shall talk generally about the state of the art in set theory and try to explain to what extent the independence results in set theory influence our understanding of mathematical foundations. The talk will start rather generally and will build up to describe some current research directions.

### 04.10.2011 (Tuesday)

#### Derivatives and Credit Contagion in Interconnected Networks

Regular Seminar Reimer Kuehn (King's)

 at: 16:00 City U.room CG02 abstract: The importance of adequately modeling credit risk has once again been highlighted in the recent financial crisis. Defaults tend to cluster around times of economic stress due to poor macro-economic conditions, but also by directly triggering each other through contagion. Although credit default swaps have radically altered the dynamics of contagion for more than a decade, models quantifying their impact on systemic risk are still missing. Here, we examine contagion through credit default swaps in a stylized economic network of corporates and financial institutions. We analyse such a system using a stochastic setting, which allows us to exploit limit theorems to exactly solve the contagion dynamics for the entire system. Our analysis shows that CDS, when used to expand banks' loan books (arguing that CDS would offload the additional risks from banks' balance sheets), can actually lead to greater instability of the entire network in times of economic stress, by creating additional contagion channels. This can lead to considerably enhanced probabilities for the occurrence of very large losses and very high default rates in the system. Our approach adds a new dimension to research on credit contagion, and could feed into a rational underpinning of an improved regulatory framework for credit derivatives.

### 23.03.2011 (Wednesday)

#### Special lecture by Prof. John McKay

Exceptional Seminar John McKay ()

 at: 16:30 City U.room CG03 abstract:

### 15.03.2011 (Tuesday)

#### Mirror Symmetry for Grassmannians

Regular Seminar Konstanze Rietsch (Kings)

 at: 16:00 City U.room AG03 abstract:

### 08.03.2011 (Tuesday)

#### Stability and wall-crossing

Regular Seminar Tom Bridgeland (Oxford)

 at: 16:00 City U.room AG03 abstract: In algebraic geometry and string theory there has been a lot of recent work on so-called wall-crossing phenomena for Donaldson-Thomas invariants. In this talk we will study a baby example of wall-crossing, which already has some non-trivial consequences. I will not assume any previous knowledge of algebraic geometry, just some basic properties of the category of modules over a ring.

### 15.02.2011 (Tuesday)

#### Reinforcement Learning in Evolutionary Games

Regular Seminar Robert Seymour (UCL)

 at: 16:00 City U.room AG03 abstract:

### 25.01.2011 (Tuesday)

#### Three Kinds of Vortex Integrability

Regular Seminar Nick Manton (DAMTP, Cambridge)

 at: 16:00 City U.room AG.03 abstract: The equations for Abelian Higgs vortices (magnetic flux vortices) on a plane or a more general surface are generally not integrable, but for vortices on a hyperbolic plane of curvature -1/2 they are. This talk will present (almost explicit) vortex solutions on certain compact hyperbolic surfaces. Also to be discussed are two asymptotically solvable problems for vortices: the effective vortex motion on a large surface with small curvature, and the structure of vortex solutions on a small surface where the vortices are about to dissolve (and the equations linearize). These results (obtained with N. Rink and with N. Romao) bring vortex theory closer to classical results on the complex and metric geometry of Riemann surfaces.

### 07.12.2010 (Tuesday)

#### Commuting conjugacy classes in groups

Regular Seminar Mark Wildon (Royal Holloway)

 at: 16:00 City U.room CG05 abstract: Let us say that two conjugacy classes of a group commute if they contain representatives that commute. When G is a finite group with a normal subgroup N such that G/N is cyclic, one can use this definition, together with Hall's Marriage Theorem, to describe the distribution of the conjugacy classes of G across the cosets of N. I will give an overview of this result, and then talk about some more recent work on commuting conjugacy classes in symmetric and general linear groups. This talk is on joint work with John Britnell.

### 23.11.2010 (Tuesday)

#### Scaling and integrability from AdS5 x S5

Regular Seminar Riccardo Ricci (Imperial College)

 at: 16:00 City U.room CG05 abstract: According to AdS/CFT a remarkable correspondence exists between strings in AdS5 x S5 and operators in N=4 SYM. A particularly important case is that of fast-spinning folded closed strings and the so called twist-operators in the gauge theory. This is a remarkable tool for uncovering and checking the detailed structure of the AdS/CFT correspondence and its integrability properties. In this talk I will show how to match the expression of the anomalous dimension of twist operators as computed from the quantum superstring with the result obtained from the Bethe ansatz of SYM. This agreement resolves a long-standing disagreement between gauge and string sides of the AdS/CFT duality and provides a highly nontrivial strong coupling test of SYM integrability.

### 16.11.2010 (Tuesday)

#### Brauer trees for finite reductive groups

Regular Seminar Olivier Dudas (Oxford University)

 at: 16:00 City U.room CG05 abstract: Some aspects of the modular representation theory of a finite group can be described by a tree. Such trees have been determined for almost all finite simple groups, but some cases remain unknown. Starting from the example of the group SL2(q) I will explain how geometric methods can be used to solve this problem for finite reductive groups.

### 09.11.2010 (Tuesday)

#### Evolution as an information dynamic system

Regular Seminar Roman Belavkin (Middlesex University)

 at: 16:00 City U.room CG05 abstract: I will speak about a new research project called 'Evolution as an information dynamic system', which involves collaboration between four universities in the United Kingdom. This is a three year project started this year, 2010, and its aim is to develop new understanding of information dynamics in evolution and biology. In particular, we are going to derive new optimality conditions for some evolutionary operators, such as mutation and recombination. Evolutionary states will be represented by probability measures on the space of genetic sequences, and different operators produce different evolution of the states. We define the optimality conditions for evolution based on the maximisation of utility (or fitness) of information principle. The optimal evolution in this sense achieves the shortest 'information distance', and it can be different from an evolution optimal in another sense, such as the shortest convergence time. We argue that the former achieves a better adaptation of organisms living in a dynam ic environment. I will present several early results related to the optimisation of mutation rate parameter. I will review these results in the light of the classical theories of adaptation (e.g. Fisher's geometric model) and error threshold. Then I will outline some future theoretical and experimental work of the project.

### 02.11.2010 (Tuesday)

#### Exact and approximate epidemic models on networks

Regular Seminar Istvan Zoltan Kiss (University of Sussex)

 at: 16:00 City U.room CG05 abstract: Many if not all models of disease transmission on networks can be linked to the exact state-based Markovian formulation. However the large number of equations for any system of realistic size limits their applicability to small populations. As a result, most modelling work relies on simulation and pairwise models. In this talk, for a simple SIS dynamics on an arbitrary network, we formalise the link between a well known pairwise model and the exact Markovian formulation and we formalise lumping and its direct link to graph automorphism. Lumping is a powerful technique that exploits graph symmetry and allows to keep the model exact while considerably reducing the number of equations. Finally, for pairwise model two different closures are presented, one well established and one that has been recently proposed. The closed dynamical systems are solved numerically and the results are compared to output from individual-based stochastic simulations. This is done for a range of networks with the same average degree and clustering coefficient but generated using different algorithms. It is shown that the ability of the pairwise system to accurately model an epidemic is fundamentally dependent on the underlying large-scale network structure. We show that the existing pairwise models work well for certain types of network but have to be used with caution as higher-order network structures may compromise their effectiveness. Keywords: network, epidemic, Markov chain, moment closure.

### 26.10.2010 (Tuesday)

#### Modular realizations of hyperbolic Weyl groups

Regular Seminar Hermann Nicolai (Albert Einstein Institute, Golm)

 at: 16:00 City U.room CG05 abstract:

### 19.10.2010 (Tuesday)

#### Discrete integrable dynamics and Somos sequences

Regular Seminar Andrew Hone (Kent)

 at: 16:00 City U.room CG05 abstract: Somos sequences are generated by a rational recurrence, which is specified by a quadratic relation between adjacent iterates. Michael Somos noticed that, for some special choices of initial values, such recurrences could unexpectedly produce sequences of integers. Examples of Somos sequences were known somewhat earlier in number theory, from Morgan Ward's elliptic analogues of Fibonacci and Lucas sequences. In algebraic combinatorics, Somos recurrences provide a basic example of the Laurent phenomenon, which is a cornerstone of Fomin and Zelevinsky's theory of cluster algebras. This introductory talk reviews the history of Somos sequences and their connections with these and other areas of mathematics and theoretical physics, including solvable statistical mechanics (the hard hexagon model) and discrete integrable systems (QRT maps and the discrete Hirota equation).

### 13.10.2010 (Wednesday)

#### Unusual singular behavior of the entanglement entropy in one dimension

Regular Seminar Francesco Ravanini (Bologna)

 at: 15:00 City U.room C322 abstract: We study the Renyi entropy of the one-dimensional XYZ spin-1/2 chain in the entirety of its phase diagram. The model has several quantum critical lines corresponding to rotated XXZ chains in their paramagnetic phase, and four tri-critical points where these phases join. Two of these points are described by a conformal field theory and close to them the entropy scales as the logarithm of its mass gap. The other two points are not conformal and the entropy has a peculiar singular behavior in their neighbors, characteristic of an essential singularity. At these non-conformal points the model undergoes a discontinuous transition, with a level crossing in the ground state and a quadratic excitation spectrum. We propose the entropy as an efficient tool to determine the discontinuous or continuous nature of a phase transition also in more complicated models.