This series consists of talks in the area of Superstring Theory.
We discuss D-brane instantons in four-dimensional string compactifications with special emphasis on Eucliden D2-branes in Type IIA orientifolds with spacetime filling D6-branes. These can induce superpotential couplings among the open string fields which are forbidden at the perturbative level since they violate some of the global U(1) symmetries generically present in string theory.
After reviewing recent developments in the study of the AdS/CFT correspondence between the IR gauge theory living on a stack of D3-branes placed at a Calabi-Yau singularity and type IIB string theory on the near horizon geometry, we focus on the problem of counting chiral BPS operators in this class of CFTs and we match them with the dual string states in the general case of toric CY. Partition functions can be explicitly written in all sectors with fixed baryonic charge using localization over fixed points of the toric actions.
Light-cone superstring field theory (LCSFT) and matrix string theory
(MST) are closely related. Both theories at the tree level are the Green-Schwarz superstring theory in the light-cone gauge. At the interaction level, the twist fields and the spin fields in MST correspond to the string interaction vertices in LCSFT. Since the CFT fields in MST are characterized by their OPEs, we would like to realize the OPEs by the interaction vertices in LCSFT to see the correspondence. In this talk I will begin with reviews of both theories and proceed to the correspondence between them.
The duality between theories of quantum strings and Yang-Mills gauge theories, in particular the AdS/CFT conjecture, has over the years given rise to many important physical insights. Recently, the realization that both sides of the duality, in certain limits, can be be described by integrable systems has lead to a good deal of progress. In this talk we will review the construction of these integrable structures and their usefulness in understanding strings in curved backgrounds/strongly coupled gauge theories.
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I will discuss some ambiguities involved in using the AdS/CFT correspondence
to calculate the ultra-relativistic jet quenching parameter for quarks moving in
an N=4 super Yang-Mills thermal bath. Along the way, I will investigate the behavior of various string configurations on a five-dimensional AdS black hole
background.
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