Strings, branes, and gravity duals of gauge theories

We study the correspondence between certain supersymmetric gauge theories and their dual supergravity descriptions. Using low-energy brane probes of the super-gravity geometries we find moduli spaces of vacua, as expected from considering the dual gauge theories. The metrics on these spaces can be put into a form consistent with field theory expectations. This provides a non-trivial check on the supergravity solutions, in addition to strong-coupling predictions for the gauge theories. In the case of N = 2 supersymmetric gauge theory, proposed supergravity duals have previously been shown, using brane probe techniques, to display the 'enhangon mechanism'. In particular, the supergravity geometries correctly reproduce the per-turbative behaviour of the gauge theory. We calculate exact non-perturbative results at low-energies using the method of Seiberg & Witten. These correctly reproduce the perturbative results in the supergravity limit, but also make predictions for when the supergravity approximation is not valid. Finally, we study the Penrose limit of a geometry that is dual to a known N= 1 superconformal gauge theory. The resulting spacetime is a new plane-wave solution with constant three-form fluxes. We quantize type IIB superstrings on this background using the Green-Schwarz formalism. We find the spectrum of string excitations and discover that it is particularly simple, due to the specific form of the plane-wave background. Using the gauge theory/gravity duality, we make predictions (beyond the supergravity approximation) for gauge theory quantities in the corresponding limit.