Supergravity and "new" six-dimensional gauge theories

In the first part of this Letter, we analyse the supergravity dual descript ions of six-dimensional field theories realized on the worldvolume of (p, q ) five-branes (OD5 theory). We show that in order for the low-energy gauge theory description to be valid the theta parameter must be rational. Irrati onal values of theta require a strongly coupled string description of the s ystem at low-energy. We discuss the phase structure and deduce some propert ies of these theories. In the second part we construct and study the superg ravity description of NS5-branes with two electric RR field, which provides a dual description of six-dimensional theories with several light open D-b rane excitations. (C) 2000 Published by Elsevier Science B.V.