Non-supersymmetric gauge theories from D-branes in Type 0 string theory

We construct non-supersymmetric four-dimensional gauge theories arising as effective theories of D-branes placed on various singularities in Type OB s tring theory. We mostly focus on models which are conformal in the large-N limit and present both examples appearing on self-dual D3-branes on orbifol d singularities and examples including orientifold planes. Moreover, we der ive type 0 Hanany-Witten setups with NS 5-branes intersected by D-branes an d the corresponding rules for determining the massless spectra. Finally, we discuss possible duality symmetries (Seiberg duality) for non-supersymmetr ic gauge theories within this framework. (C) 1999 Elsevier Science B,V, All rights reserved.