Holographic particle detection

In anti--de Sitter (AdS) space, classical supergravity solutions are represented ``holographically'' by conformal field theory (CFT) states in which operators have expectation values. These 1-point functions are directly related to the asymptotic behavior of bulk fields. In some cases, distinct supergravity solutions have identical asymptotic behavior; therefore, dual expectation values are insufficient to distinguish them. We argue that non-local objects in gauge theory can resolve the ambiguity, and explicitly show that collections of point particles in AdS₃ can be detected by studying kinks in dual CFT Green functions. Three dimensional black holes can be formed by the collision of such particles. We show how black hole formation can be detected in the holographic dual, and calculate CFT quantities that are sensitive to the distribution of matter inside the event horizon.