Branes, superpotentials and superconformal fixed points

We analyze various brane configurations corresponding to field theories in three, four and five dimensions, We find brane configurations which correspond to three-dimensional N = 2 and four-dimensional N = 1 supersymmetric QCD theories with quartic superpotentials, in which what appear to be ''hidden parameters'' play an important role. We discuss the construction of five-dimensional N = 1 supersymmetric gauge theories and superconformal fixed points using branes, which leads to new five-dimensional N = 1 superconformal field theories. The same five-dimensional theories are also used, in a surprising way, to describe new superconformal fixed points of three-dimensional N = 2 supersymmetric theories, which have both ''electric'' and ''magnetic'' Coulomb branches. (C) 1997 Elsevier Science B.V. PACS: 11.10.Kk; 11.30.Pb.