Forthcoming Seminars

Mon, 02/03/2009
12:00 		Volker Braun (Dublin Institute of Advanced Studies) String Theory Seminar Add to calendar L3
Calabi-Yau Groups
Conjecturally, there are only finitely many possible fundamental groups of Calabi-Yau manifolds. I will start by reviewing some of the known examples of such "Calabi-Yau groups" and their importance or string theory. Then I will present some progress towards the classification of the free quotients of complete intersection Calabi-Yau manifolds in products of projective spaces.
Mon, 02/03/2009
14:15 		Professor Marta Sanz Solé (Universitat de Barcelona) Stochastic Analysis Seminar Add to calendar Oxford-Man Institute
Some criteria for hitting probabilities. Application to systems of stochastic wave equation with additive noise
We develop several results on hitting probabilities of random fields which highlight the role of the dimension of the parameter space. This yields upper and lower bounds in terms of Hausdorff measure and Bessel-Riesz capacity, respectively. We apply these results to a system of stochastic wave equations in spatial dimension k≥1 driven by a d-dimensional spatially homogeneous additive Gaussian noise that is white in time and coloured in space.
Mon, 02/03/2009
15:00 		Martin Bays (Oxford) Logic Seminar Add to calendar SR1
Choices of division sequences on complex elliptic curves
Let $ \mathbb{E} $ be an elliptic curve defined over a number field $ k $, and let $ a\in\mathbb{E}(\mathbb{C}) $ be a complex point. Among the possible choices of sequences of division points of $ a $, $ (a_n)_n $ such that $ a_1 = a $ and $ na_{nm} = a_m $, we can pick out those which converge in the complex topology to the identity. We show that the algebraic content of this effect of the complex topology is very small, in the sense that any set of division sequences which shares certain obvious algebraic properties with the set of those which converge to the identity is conjugated to it by a field automorphism of $ \mathbb{C} $ over $ k $. As stated, this is a result of algebra and number theory. However, in proving it we are led ineluctably to use model theoretic techniques - specifically the concept of "excellence" introduced by Shelah for the analysis of $ L_{\omega_1,\omega} $ categoricity, which reduces the question to that of proving certain unusual versions of the theorems of Mordell-Weil and Kummer-Bashmakov. I will discuss this and other aspects of the proof, without assuming any model- or number-theoretic knowledge on the part of my audience.
Mon, 02/03/2009
15:45 		Jacob Rasmussen (Cambridge) Topology Seminar Add to calendar L3
The Alexander polynomial of sutured manifolds
The notion of a sutured 3-manifold was introduced by Gabai. It is a powerful tool in 3-dimensional topology. A few years ago, Andras Juhasz defined an invariant of sutured manifolds called sutured Floer homology. I'll discuss a simpler invariant obtained by taking the Euler characteristic of this theory. This invariant turns out to have many properties in common with the Alexander polynomial. Joint work with Stefan Friedl and Andras Juhasz.
Mon, 02/03/2009
15:45 		Professor Yue-Yun Hu (Université Paris XIII) Stochastic Analysis Seminar Add to calendar Oxford-Man Institute
Minimal position in branching random walk
This talk is based on a joint work with Zhan Shi: We establish a second-order almost sure limit theorem for the minimal position in a one-dimensional super-critical branching random walk, and also prove a martingale convergence theorem which answers a question of Biggins and Kyprianou (2005). Our method applies furthermore to the study of directed polymers on a disordered tree. In particular, we give a rigorous proof of a phase transition phenomenon for the partition function (from the point of view of convergence in probability), already described by Derrida and Spohn (1988). Surprisingly, this phase transition phenomenon disappears in the sense of upper almost sure limits.
Mon, 02/03/2009
16:00 		Sebastian Pancratz (Mathematical Institute, Oxford) Junior Number Theory Seminar Add to calendar SR1
Classical Primality Testing
This talk will mention methods of testing whether a given integer is prime. Included topics are Carmichael numbers, Fermat and Euler pseudo-primes and results contingent on the Generalised Riemann Hypothesis.
Mon, 02/03/2009
17:00 		Luis Escauriaza (Universidad del País Vasco) Partial Differential Equations Seminar Add to calendar Gibson 1st Floor SR
Hardy's Uncertainty Principle, Convexity and Schrödinger Evolutions
Tue, 03/03/2009
14:30 		Malwina Luczak (LSE) Combinatorial Theory Seminar Add to calendar L3
Concentration and mixing for Markov chains
We consider Markovian models on graphs with local dynamics. We show that, under suitable conditions, such Markov chains exhibit both rapid convergence to equilibrium and strong concentration of measure in the stationary distribution. We illustrate our results with applications to some known chains from computer science and statistical mechanics.
Tue, 03/03/2009
15:30 		V. A. Solonnikov (Steklov Institute of Mathematics) OxPDE Lunchtime Seminar Add to calendar Gibson 1st Floor SR
Linearisation principle for a system of equations of mixed type
Tue, 03/03/2009
15:45 		Brent Doran (Oxford) Algebraic and Symplectic Geometry Seminar Add to calendar L3
On stably rational varieties
Tue, 03/03/2009
17:00 		Markus Linckelmann (University of Aberdeen) Algebra Seminar Add to calendar L2
Hochschild and block cohomology varieties are isomorphic
Thu, 05/03/2009
11:00 		Professor Bao Chau Ngo (Princeton and Universite Paris-Sud) Special Seminar Add to calendar L2
Decomposition theorem for abelian fibrations
Derived direct image of a proper map with smooth source is a direct sum of simple perverse sheaves with shifts in the degrees. The supports of these simple perverse sheaves are obviously important  topological invariants of the map. In general, it is difficult to determine these supports. This is possible for an abelian fibration under some assumptions. This determination has some amazing  consequences on equality of number of points of certain algebraic varieties over finite fields and in particular, it implies the so called fundamental lemma in Langlands' program.
Thu, 05/03/2009
12:00 		David Baraglia (Oxford) Junior Geometry and Topology Seminar Add to calendar SR1
Semi-flat fibrations of special Lagrangian and coassociative submanifolds
I will go over my paper (arXiv:0902.2135v1) which explains how semi-flat Calabi-Yau / G$ _2 $ manifolds can be constructed from minimal 3-submanifolds in a signature (3,3) vector space.
Thu, 05/03/2009
13:00 		Robert Griffiths (Department of Statistics, Oxford) Mathematical Finance Internal Seminar Add to calendar DH 3rd floor SR
Diffusion processes and coalescent trees.
Diffusion process models for evolution of neutral genes have a particle dual coalescent process underlying them. Models are reversible with transition functions having a diagonal expansion in orthogonal polynomial eigenfunctions of dimension greater than one, extending classical one-dimensional diffusion models with Beta stationary distribution and Jacobi polynomial expansions to models with Dirichlet or Poisson Dirichlet stationary distributions. Another form of the transition functions is as a mixture depending on the mutant and non-mutant families represented in the leaves of an infinite-leaf coalescent tree. The one-dimensional Wright-Fisher diffusion process is important in a characterization of a wider class of continuous time reversible Markov processes with Beta stationary distributions originally studied by Bochner (1954) and Gasper (1972). These processes include the subordinated Wright-Fisher diffusion process.

For any corrections/updates to these listings, please contact seminars [-at-] maths [dot] ox [dot] ac [dot] uk.

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