Thu, 31 Jan 2013

16:00 - 17:00
L3

Classicality for overconvergent eigenforms on some Shimura varieties.

Christian Johansson
(Imperial College London)
Abstract

A well known theorem of Coleman states that an overconvergent modular eigenform of weight k>1 and slope less than k-1 is classical. This theorem was later reproved and generalized using a geometric method very different from Coleman's cohomological approach. In this talk I will explain how one might go about generalizing the cohomological method to some higher-dimensional Shimura varieties.

Thu, 24 Jan 2013

16:00 - 17:00
L3

p-adic functoriality for inner forms of unitary groups.

Judith Ludwig
(Imperial College London)
Abstract

In this talk I will explain a notion of p-adic functoriality for inner forms of definite unitary groups. Roughly speaking, this is a morphism between so-called eigenvarieties,  which are certain rigid analytic spaces parameterizing p-adic families  of automorphic forms. We will then study certain properties of classical Langlands functoriality that allow us to prove p-adic functoriality in some "stable" cases.

Thu, 17 Jan 2013

16:00 - 17:00
L3

Computing the local Cassels-Tate pairing.

Rachel Newton
(Leiden University)
Abstract

Let K be a number field and E/K be an elliptic curve. Multiplication by n induces a map from the n^2-Selmer group of E/K to the n-Selmer group. The image of this map contains the image of E(K) in the n-Selmer group and is often smaller. Thus, computing the image of the n^2-Selmer group under multiplication by n can give a tighter bound on the rank of E/K. The Cassels-Tate pairing is a pairing on the n-Selmer group whose kernel is equal to the image of the n^2-Selmer group under multiplication by n. For n=2, Cassels gave an explicit description of the Cassels-Tate pairing as a sum of local pairings and computed the local pairing in terms of the Hilbert symbol. In this talk, I will give a formula for the local Cassels-Tate pairing for n=3 and describe an algorithm to compute it for n an odd prime. This is joint work with Tom Fisher.

Mon, 28 Jan 2013

12:00 - 13:00
L3

Reductions with reduced supersymmetry in generalized geometry

Mariana Graña
(CEA/Saclay)
Abstract
We will discuss supersymmetric reductions of type II and M-theory down to four dimensions, in the language of exceptional generalized geometry (EGG). EGG is the extension of generalized complex geometry which also geometrizes the RR fields, and is therefore the relevant language to use in M-theory. After a brief introduction to EGG, we will present the algebraic structures that encode all information about the lower-dimensional action, concentrating on the case of N=2 supersymmetry. We will show, in particular, that these structures have a nice description using an 8-dimensional tangent space, where they look like pure spinors as in generalized complex geometry.
Mon, 21 Jan 2013

12:00 - 13:00
L3

Umbral Moonshine

Miranda Cheng
(Jussieu)
Abstract
Mock modular forms are generalizations of modular forms first introduced by Ramanujan. Their properties had been mysterious for 80 years until various breakthroughs in the past 10 years. In the last century, the Monstrous Moonshine Conjecture initiated the study of the fascinating relation between modular forms and sporadic groups. In this talk I will report a conjecture on a new type of "umbral moonshine" relating a set of mock modular forms, including many of Ramanujan's original examples, and the representation theory of a set of finite groups. One instance of such a surprising umbral moonshine phenomenon relates the largest Mathieu group to the elliptic genus of K3 surfaces, as was first observed by Euguchi-Ooguri-Tachikawa in 2010. Moreover, there are hints suggesting that all occurrences of umbral moonshine have a close relation to K3-compactifications of string theory. However, despite of these tantalising hints the origin and the explanation of this umbral moonshine is still unclear at the moment. This talk is based on the arXiv pre-print: 1201.4140, 1204.2779 with John Duncan and Jeff Harvey.
Mon, 14 Jan 2013

12:00 - 13:00
L3

Non-commuting closed strings on non-geometric backgrounds

Magdalena Larfors
(Oxford)
Abstract
Strings are extended objects, and this means that they can be compactified not only on Riemannian manifolds, but also on more exotic spaces with generalized transition functions. An example of this is the T-fold, where T-duality is used to glue the Neveu-Schwarz fields of the background. Collectively, these exotic set-ups are known as non-geometric string compactifications, and in this talk I will discuss two of their aspects. First, I will present a field redefinition in the Neveu-Schwarz sector that allows a ten-dimensional, effective description of certain non-geometric backgrounds. This redefinition is inspired by Generalized Geometry and Double Field Theory. Second, I will show that closed strings become non-commuting when non-geometric fluxes are turned on. This will be done through the analysis of a three-torus with H-flux and its T-dual configurations.
Tue, 15 Jan 2013

12:00 - 13:00
L3

Supersymmetric loop space

Mir Faizal
Abstract

We will first review the construction of N =1

supersymmetric Yang-Mills theory in three dimensions. Then we will

construct a superloop space formulation for this super-Yang-Mills

theory in three dimensions.Thus, we will obtain expressions for loop

connection and loop curvature in this superloop space. We will also

show that curvature will vanish, unless there is a monopole in the

spacetime. We will also construct a quantity which will give the

monopole charge in this formalism. Finally, we will show how these

results hold even in case of deformed superspace.

Thu, 24 Jan 2013

14:00 - 15:00
L3

Cocycle twists of tensor categories and of rational Cherednik algebras

Yuri Bazlov
(Manchester University)
Abstract

Central extensions of a finite group G correspond to 2-cocycles on G, which give rise to an abelian cohomology group known as the Schur

multiplier of G. Recently, the Schur multiplier was defined in a much more

general setting of a monoidal category. I will explain how to twist algebras by categorical 2-cocycles and will mention the role of

such twists the theory of quantum groups. I will then describe an approach to twisting rational Cherednik algebras by cocycles,

and will discuss possible applications of this new construction to the representation theory of these algebras.

Thu, 07 Mar 2013

17:00 - 18:00
L3

Pure Inductive Logic

Jeff Paris
(Manchester)
Abstract

I shall give a non-technical survey of Pure Inductive Logic, a branch of Carnap's Inductive Logic which was

anticipated early on in that subject but has only recently begun to be developed as an area of Mathematical Logic. My intention

is to cover its origins and aims, and to pick out some of the key concepts which have emerged in the last decade or so.

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