Past String Theory Seminar

8 June 2015
12:00
Abstract

It has been conjectured that the fundamental theory of strings and branes has an $E_{11}$ symmetry. I will explain how this conjecture  leads to  a generalised space-time,  which is automatically equipped with its own geometry, as well as equations of motion for the fields that live on this generalised space-time.

 

  • String Theory Seminar
1 June 2015
12:00
Abstract

Form factors form a bridge between the purely on-shell amplitudes and the purely off-shell correlation functions. In this talk, we study the form factors of general gauge-invariant local composite operators in N=4 SYM theory via on-shell methods. At tree-level and for a minimalnumber of external fields, the form factor exactly realises the spin-chain picture of N=4 SYM theory in the language of scattering amplitudes. Via generalised unitarity, we obtain the cut-constructible part of the one-loop correction to the minimal form factor of a generic operator. Its UV divergence yields the complete one-loop dilatation operator of the theory. At two-loop order, we employ unitarity to calculate the minimal form factors and thereby the dilatation operator for the Konishi primary operator and all operators in the SU(2) sector. For the former operator as well as other non-protected operators, important subtleties arise which require an extension of the method of unitarity.

  • String Theory Seminar
27 April 2015
12:00
Philip Candelas
Abstract

Recently, as part of a project to find CY manifolds for which both the Hodge numbers (h^{11}, h^{21}) are small, manifolds have been found with Hodge numbers (4,1) and (1,1). The one-dimensional special geometries of their complex structures are more complicated than those previously studied. I will review these, emphasising the role of the fundamental period and Picard-Fuchs equation. Two arithmetic aspects arise: the first is the role of \zeta(3) in the monodromy matrices and the second is the fact, perhaps natural to a number theorist, that through a study of the CY manifolds over finite fields, modular functions can be associated to the singular manifolds of the family. This is a report on joint work with Volker Braun, Xenia de la Ossa and Duco van Straten.

  • String Theory Seminar
9 March 2015
12:00
Tudor Dimofte
Abstract
While the Higgs branch of a 3d N=4 gauge theory is protected from quantum corrections and its metric is easily computable, the Coulomb branch suffers both perturbative and nonperturbative corrections, and has long remained mysterious. I will present a construction of the Coulomb branch as a complex manifold, and (in principle) as a hyperkahler manifold. In particular, holomorphic functions on the Coulomb branch come from vevs of monopole operators in a chiral ring, and it turns out that this ring has a simple, quasi-abelian description. Applying the construction to linear quiver gauge theories, one finds new descriptions of singular monopole moduli spaces. I may also touch upon relations to equivariant vortex counting, geometric representation theory, and symplectic duality.
  • String Theory Seminar
2 March 2015
12:00
George Papadopoulos
Abstract

I shall demonstrate, under some mild assumptions, that the symmetry group of  extreme, Killing, supergravity horzions contains an sl(2, R) subalgebra.  The proof requires a generalization of the  Lichnerowicz theorem for non-metric connections. The techniques developed can also be applied in the classification
of AdS and Minkowski flux backgrounds.
 

  • String Theory Seminar
23 February 2015
12:00
Abstract
The spectrum of BPS states in four-dimensional gauge theories and string vacua with N=2 supersymmetry is well-known to be jump across certain walls in moduli space, where bound states can decay. In this talk I will survey how the discontinuity can be understood in terms of the supersymmetric quantum mechanics of mutually non-local point particles. This physical picture 
suggests that, at any point in moduli space, the BPS spectrum can be viewed as a sum of bound states of absolutely stable `single-centered' constituents. This idea appears to be vindicated in the context of quiver moduli spaces. Finally, I shall explain how the discontinuous BPS indices can be combined into a `new' supersymmetric index, a function which sums up multi-particle state contributions and is continuous across the wall.
  • String Theory Seminar

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