Mon, 11 May 2009

12:00 - 13:00
L3

Twistor Methods for Scattering Amplitudes

David Skinner
(Oxford)
Abstract
Abstract:  Modern techniques for computing multi-particle and multi-loop scattering amplitudes rely on a sophisticated use of on-shell recursion relations and generalised unitarity methods. I will show that these methods are ideally suited to interpretation in twistor space, where superconformal properties become manifest. In fact, the recursion relations of Britto, Cachazo, Feng & Witten provide a clear framework for the twistor diagram program initiated in the 1970s.
 Tree-level scattering amplitudes in N=4 SYM are now known to possess a Yangian symmetry, formed by combining the original PSU(2,2|4) superconformal invariance with a second "dual" copy. I will also discuss very recent work constructing scattering amplitudes in a twistor space in which this dual superconformal symmetry acts geometrically.
Mon, 25 May 2009

12:00 - 13:00
L3

Cybersusy--a new mechanism for supersymmetry breaking in the standard supersymmetric mode

John Dixon
Abstract
Abstract: Cybersusy is a new approach to supersymmetry breaking, based on the BRS cohomology of composite operators in the supersymmetric standard model (analyzed using spectral sequences). The cohomology generates a new kind of supersymmetry algebra and a new effective action.  When the gauge symmetry is broken (from the vacuum expectation value of a scalar field), supersymmetry breaking is also induced. Applied to the leptons, the result is consistent with experiment, and the vacuum energy remains zero, and no annoying mass sum rules are present.
Mon, 18 May 2009

12:00 - 13:00
L3

Dynamical Logic

Fay Dowker
(Imperial College)
Abstract
Abstract: Despite the high regard in which physicists hold General Relativity, the spacetime nature of reality has not yet fully been taken to heart in addressing the question of the interpretation of quantum mechanics. Partial progress was made by Dirac and Feynman by casting the dynamical content of quantum theory in terms of a Sum Over (spacetime) Histories (SOH). Recently it has been suggested by Sorkin that this SOH is part of an interpretive framework in which the rules of inference that are used to reason about physical reality are themselves subject to dynamical law. Just as General Relativity showed that geometry is not fixed and absolute, so Quantum Mechanics may be telling us that logical rules of inference are not fixed but part of physics.
Mon, 04 May 2009

12:00 - 13:00
L3

(0,2) Landau-Ginzburg Models and Residues

Ilarion Melnikov
(Max Planck Institute)
Abstract
Abstract: I will discuss techniques for the computation of correlators in (0,2) Landau-Ginzburg models.  After introducing these theories from the point of view of heterotic compactifications, I will describe the associated half-twisted models and their basic algebraic structure.  This structure enables direct computation of correlators and suggests a generalization of the Grothendieck residue.
Mon, 27 Apr 2009

12:00 - 13:00
L3

Twistor diagrams for gauge-theoretic amplitudes

Andrew Hodges
(Oxford)
Abstract
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.
Tue, 23 Jun 2009

15:45 - 16:45
L3

Homological Mirror Symmetry for the 4-torus

Ivan Smith
(Cambridge)
Abstract

I will describe joint work with Mohammed Abouzaid, in which we complete the proof of homological mirror symmetry for the standard four-torus and consider various applications. A key tool is the recently-developed holomorphic quilt theory of Mau-Wehrheim-Woodward.

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