An orbifold of Type 0B strings and non-supersymmetric gauge theories

We study a Z(2) orbifold of Type DB string theory by reflection of six of t he coordinates (this theory may also be thought of as a Z(4) orbifold of Ty pe IIB by a rotation by pi in three independent planes). We show that the o nly massless mode localized on the fixed fourplane R-3.1 is a U(1) gauge fi eld. After introducing D3-branes parallel to the fixed fourplane we find no n-supersymmetric non-abclian gauge theories on their worldvolume. One of ou r results is that the theory on equal numbers of electric and magnetic D3-b ranes placed at the fourplane is the Z(4) orbifold of N = 4 supersymmetric Yang-Mills theory by the center of its R-symmetry group. (C) 2000 Elsevier Science B.V. All rights reserved.