String Theory Seminar
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Mon, 18/01/2010 12:00 |
Daniel Thompson (Queen Mary, UL) |
String Theory Seminar  |
L3 |
| In this talk I will be discussing some reformulations of string theory which promote T-duality to the level of a manifest symmetry namely Hull's Doubled Formalism and Klimcik and Severa's Poisson-Lie T-duality. Such formalisms double the number of fields but also incorporate some chirality-like constraint. Invoking this constraint leads one to consider sigma-models which, though duality invariant, do not possess manifest Lorentz Invariance. Whilst such formalisms make sense at a classical level their quantum validity is less obvious. I address this issue by examining the renormalization of these duality invariant sigma models. This talk is based upon both forthcoming work and recent work in arXiv:0910.1345 [hep-th] and its antecedents arXiv:0708.2267, arXiv:0712.1121. | |||
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Mon, 25/01/2010 12:00 |
Yang-Hui He (Oxford) |
String Theory Seminar |
L3 |
| 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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Mon, 01/02/2010 12:00 |
Lionel Mason (Oxford) |
String Theory Seminar |
L3 |
| 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. | |||
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Mon, 08/02/2010 12:00 |
Jerome Gauntlett (Imperial College) |
String Theory Seminar |
L3 |
| 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. | |||
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Mon, 15/02/2010 12:00 |
Sergio Benvenuti (Imperial College) |
String Theory Seminar |
L3 |
| 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. | |||
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Mon, 22/02/2010 12:00 |
Riccardo Ricci (Imperial College) |
String Theory Seminar |
L3 |
| 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. | |||
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Mon, 01/03/2010 12:00 |
Alistair King (Bath) |
String Theory Seminar |
L3 |
