BRANES AND 6-DIMENSIONAL SUPERSYMMETRIC THEORIES

We consider configurations of six-branes, five-branes and eight-branes in various superstring backgrounds, These configurations give rise to (0, 1) supersymmetric theories in six dimensions. The condition for R R charge conservation of a brane configuration translates to the condi tion that the corresponding field theory is anomaly-free. Sets of infi nitely many models with non-trivial RG fixed points at strong coupling are demonstrated. Some of them reproduce and generalize the world-vol ume theories of SO(32) and E-8 x E-8 small instantons. All the models are shown to be connected by smooth transitions. In particular, the sm all instanton transition for which a tensor multiplet is traded for 29 hypermultiplets is explicitly demonstrated, The particular limit in w hich these theories can be considered as six-dimensional string theori es without gravity are discussed. New fixed points (string theories) a ssociated with E-n global symmetries are discovered by taking the stro ng string coupling limit. (C) 1998 Elsevier Science B.V.