Field theory questions for string theory answers

Abstract We discuss the field theory of 3-brane probes in F-theory compactifications in two configurations, generalizing the work of Sen and of Banks, Douglas and Seiberg. One configuration involves several parallel 3-brane probes in F-theory compactified on T 4 / Z 2 , while the other invloves a compactification of F-theory on T 6 / Z 2 × Z 2 (which includes intersecting D 4 singularities). In both cases string theory provides simple pictures of the space-time theory, whose implications for the 3-brane world-volume theories are discussed. In the second case the field theory on the probe is an unusual N = 1 superconformal theory, with exact electric-magnetic duality. Several open questions remain concerning the description of this theory.