Tue, 26 Jan 2010
12:00
L3

Gravity Quantized

Jerzy Lewandowski
(Warsaw)
Abstract

Canonical quantization of gravitational field will beconsidered. Examples for which the procedure can be completed (without reducingthe degrees of freedom) will be presented and discussed. The frameworks appliedwill be: Loop Quantum Gravity, relational construction of the Dirac observablesand deparametrization.

 

Tue, 19 Jan 2010

14:30 - 15:30
L3

Shadows and intersections: stability and new proofs

Peter Keevash
(QMUL)
Abstract
We give a short new proof of a version of the Kruskal-Katona theorem due to Lov\'asz. Our method can be extended to a stability result, describing the approximate structure of configurations that are close to being extremal, which answers a question of Mubayi. This in turn leads to another combinatorial proof of a stability theorem for intersecting families, which was originally obtained by Friedgut using spectral techniques and then sharpened by Keevash and Mubayi by means of a purely combinatorial result of Frankl. We also give an algebraic perspective on these problems, giving yet another proof of intersection stability that relies on expansion of a certain Cayley graph of the symmetric group, and an algebraic generalisation of Lov\'asz’s theorem that answers a question of Frankl and Tokushige.
Mon, 01 Feb 2010

12:00 - 13:00
L3

Twistor-Strings, Grassmannians and Leading Singularities

Lionel Mason
(Oxford)
Abstract
A systematic procedure is derived for obtaining an explicit, L-loop leading singularities of planar N=4 super Yang-Mills scattering amplitudes in twistor space directly from their momentum space channel diagrams. The expressions are given as integrals over the moduli of connected, nodal curves in twistor space whose degree and genus matches expectations from twistor-string theory. We propose that a twistor-string theory for pure N=4 super Yang-Mills, if it exists, is determined by the condition that these leading singularity formulae arise as residues when an unphysical contour for the path integral is used, by analogy with the momentum space leading singularity conjecture. We go on to show that the genus g twistor-string moduli space for g-loop N^{k-2}MHV amplitudes may be mapped into the Grassmannian G(k,n). Restricting to a leading singularity, the image of this map is a 2(n-2)-dimensional subcycle of G(k,n) of exactly the type found from the Grassmannian residue formula of Arkani-Hamed, Cachazo, Cheung and Kaplan. Based on this correspondence and the Grassmannian conjecture, we deduce restrictions on the possible leading singularities of multi-loop N^pMHV amplitudes. In particular, we argue that no new leading singularities can arise beyond 3p loops.
Mon, 22 Feb 2010

12:00 - 13:00
L3

Generalized scaling and integrability from AdS5 x S5

Riccardo Ricci
(Imperial College)
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.
Mon, 15 Feb 2010

12:00 - 13:00
L3

N=2 Superconformal Theories and M5 branes

Sergio Benvenuti
(Imperial College)
Abstract
In 2009 there was progress in understanding and classifying the set of four dimensional field theories with N=2 SUSY. These models arise as M5 branes wrapped over a Riemann surface. We review this construction and describe a five dimensional point of view, using (p,q)-webs of 5-branes in Type IIB string theory. This point of view makes many properties of the theories explicit. We will also touch on the AGT correspondence, that associates a 2-dimensional CFT, similar to the Liouville CFT, to the protected sector of four dimensional N=2 models.
Mon, 08 Feb 2010

12:00 - 13:00
L3

Holographic Superconductors in M-Theory

Jerome Gauntlett
(Imperial College)
Abstract
By constructing black hole solutions of D=11 supergravity we analyse the phase diagram of a certain class of three dimensional conformal field theories at finite temperature and finite charge density. The system exhibits superconductivity at lotemperatures and furthermore at zero tmeperature and finite charge density the system exhibits an emergent quantum critical behaviour with conformal symmetry. The construction of the black hole solutions rely on a new understanding of Kaluza-Klein reductions on seven dimensional Sasaki-Einstein manifolds.
Mon, 25 Jan 2010

12:00 - 13:00
L3

Scanning through Heterotic Vacua

Yang-Hui He
(Oxford)
Abstract
We discuss some recent progress in obtaining the exact spectrum of the MSSM from a generalized embedding of the heterotic string. Utilizing current developments in algebraic geometry, especially algorithmic, we search through the landscape of vector bundles over Calabi-Yau manifolds for a special corner wherein such exact models may be found.
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