Forthcoming Seminars
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Mon, 27/04/2009 12:00 |
Andrew Hodges (Oxford) |
String Theory Seminar  |
L3 |
| Abstract: The recent paper by Arkani-Hamed, Cachazo, Cheung and Kaplan on 'The S-matrix in Twistor Space' (hep-th/0903.2110v2) has envigorated the project of expressing scattering amplitudes for (supersymmetric) gauge theory and gravity entirely in terms of twistor geometry. I shall review these new developments of twistor diagram theory, with some illustrations of its computational value. I shall also emphasise the many outstanding problems in the formalism. One of these, which Arkani-Hamed has highlighted, is the asymmetry in the representation of the amplitudes and the 'spurious poles' that arise. So far, the twistor diagram formalism has simply reproduced the less than satisfactory features of the (supersymmetrised) BCFW recursion. I will outline some new twistor-geometric results which address and partially resolve this problem. | |||
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Mon, 27/04/2009 14:15 |
Peter Moerters (Bath) |
Stochastic Analysis Seminar |
Oxford-Man Institute |
| The parabolic Anderson model is the Cauchy problem for the heat equation with random potential. It offers a case study for the possible effects that a random, or irregular environment can have on a diffusion process. In this talk I review results obtained for an extreme case of heavy-tailed potentials, among the effects we discuss our intermittency, strong localisation and ageing. | |||
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Mon, 27/04/2009 14:15 |
Gilles Carron (Nantes) |
Geometry and Analysis Seminar |
L3 |
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Mon, 27/04/2009 15:45 |
Andras Juhasz (Cambridge) |
Topology Seminar |
L3 |
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Mon, 27/04/2009 15:45 |
Prof Sondiphon Adhikari (Swansea) |
Stochastic Analysis Seminar |
Oxford-Man Institute |
| Numerical computer codes implementing physics based models are the backbone of today's mechanical/aerospace engineering analysis and design methods. Such computational codes can be extremely expensive consisting of several millions of degrees of freedom. However, large models even with very detailed physics are often not enough to produce credible numerical results because of several types of uncertainties which exist in the whole process of physics based computational predictions. Such uncertainties include, but not limited to (a) parametric uncertainty (b) model inadequacy; (c) uncertain model calibration error coming from experiments and (d) computational uncertainty. These uncertainties must be assessed and systematically managed for credible computational predictions. This lecture will discuss a random matrix approach for addressing these issues in the context of complex structural dynamic systems. An asymptotic method based on eigenvalues and eigenvectors of Wishart random matrices will be discussed. Computational predictions will be validated against laboratory based experimental results. | |||
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Mon, 27/04/2009 17:00 |
Michele Bartuccelli (University of Surrey) |
Partial Differential Equations Seminar |
Gibson 1st Floor SR |
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Tue, 28/04/2009 12:00 |
Quantum Field Theory Seminar |
L3 | |
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Tue, 28/04/2009 15:45 |
Geordie Williamson (Oxford) |
Algebraic and Symplectic Geometry Seminar |
L3 |
| Triply graded link homology (introduced by Khovanov and Rozansky) is a categorification of the HOMFLYPT polynomial. In this talk I will discuss recent joint work with Ben Webster which gives a geometric construction of this invariant in terms of equivariant constructible sheaves. In this framework the Reidemeister moves have quite natural geometric proofs. A generalisation of this construction yields a categorification of the coloured HOMFLYPT polynomial, constructed (conjecturally) by Mackay, Stosic and Vaz. I will also describe how this approach leads to a natural formula for the Jones-Ocneanu trace in terms of the intersection cohomology of Schubert varieties in the special linear group. | |||
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Tue, 28/04/2009 17:00 |
Stephen Wills (University College Cork) |
Functional Analysis Seminar |
L3 |
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Tue, 28/04/2009 17:00 |
Peter Fiebig (Universitat Freiburg) |
Algebra Seminar |
L2 |
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Wed, 29/04/2009 11:30 |
Richard Williamson (University of Oxford) |
Algebra Kinderseminar |
ChCh, Tom Gate, Room 2 |
| Presheaves on categories crop up everywhere! In this talk, I'll give a gentle introduction to 2-categories, and discuss the notion of a presheaf on a 2-category. In particular, we'll consider which 2-categories such a presheaf might take values in. Only a little familiarity with the notion of a category will be assumed! | |||
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Thu, 30/04/2009 10:00 |
Michael Harris (Univ. Paris 7, Institut Univ. de France, visiting Oxford) |
Special Lecture |
L3 |
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Thu, 30/04/2009 11:00 |
Prof. Boris Zilber (Oxford) |
Advanced Logic Class |
SR1 |
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Thu, 30/04/2009 12:00 |
Oscar Randal-Williams (Oxford) |
Junior Geometry and Topology Seminar |
SR1 |
| I will present a new proof of Mumford's conjecture on the rational cohomology of moduli spaces of curves, which is substantially different from those given by Madsen–Weiss and Galatius–Madsen–Tillmann–Weiss: in particular, it makes no use of Harer–Ivanov stability for the homology of mapping class groups, which played a decisive role in the previously known proofs. This talk represents joint work with Soren Galatius. | |||
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Thu, 30/04/2009 13:00 |
Raphael Hauser |
Mathematical Finance Internal Seminar |
DH 1st floor SR |
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Thu, 30/04/2009 14:00 |
Prof. Andrew Stuart (University of Warwick) |
Computational Mathematics and Applications |
Comlab |
| Inverse problems are often ill-posed, with solutions that depend sensitively on data. Regularization of some form is often used to counteract this. I will describe an approach to regularization, based on a Bayesian formulation of the problem, which leads to a notion of well-posedness for inverse problems, at the level of probability measures. The stability which results from this well-posedness may be used as the basis for understanding approximation of inverse problems in finite dimensional spaces. I will describe a theory which carries out this program. The ideas will be illustrated with the classical inverse problem for the heat equation, and then applied to so more complicated inverse problems arising in data assimilation, such as determining the initial condition for the Navier-Stokes equation from observations. | |||
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Thu, 30/04/2009 14:30 |
Emmanuel Letellier (Caen) |
Representation Theory Seminar |
L3 |
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Thu, 30/04/2009 16:00 |
Yuri Bilu (Bordeaux) |
Number Theory Seminar |
L3 |
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Thu, 30/04/2009 16:30 |
James Gleeson (University of Limerick) |
Differential Equations and Applications Seminar |
DH 1st floor SR |
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Thu, 30/04/2009 17:00 |
Ivan Tomasic |
Logic Seminar |
L3 |
| Difference schemes constitute important building blocks in the model-theoretic study of difference fields. Our goal is to pursue their number-theoretic aspects much further than required by model theory. Roughly speaking, a difference scheme (variety) is a scheme (variety) with a distinguished endomorphism. We will explain how to extend the methods of etale cohomology to this context and, time permitting, we will show the calculation of difference etale cohomology in some interesting cases. | |||
