Sphalerons, merons, and unstable branes in AdS space

We construct unstable classical solutions of Yang-Mills theories and their dual unstable states of type IIB on anti-de Sitter (AdS₅) space. An example is the unstable DO-brane of type IIB located at the center of AdS space. This has a field theory dual which is a sphaleron in gauge theories on S³XR. We argue that the two are dual because both are sphalerons associated with the topology of the instanton or D-instanton. This agreement provides a non-supersymmetric test of the AdS-conformal field theory duality. As an illustration, many aspects of Sen's hypothesis regarding the unstable branes can be seen easily in the weakly coupled dual field theory description. In Euclidean AdS space the DO-branes are dual to gauge theory merons. This implies that the two ends of a D0-brane world-line carry half the charge of a D-instanton. Other examples involve unstable strings in the Coulomb phase.