A NONSUPERSYMMETRIC OPEN-STRING THEORY AND S-DUALITY

A non-supersymmetric ten-dimensional open-string theory is constructed as an orbifold of type I string theory, and as an orientifold of the bosonic type B theory. It is purely bosonic, and cancellation of massl ess tadpoles requires the gauge group to be SO(32) x SO(32). The spect rum of the theory contains a closed-string tachyon, and open-string ta chyons in the (32,32) multiplet. The D-branes of this theory are analy zed, and it is found that the massless excitations of one of the 1-bra nes coincide with the world-sheet degrees of freedom of the D = 26 bos onic string theory compactified on the SO(32) lattice, This suggests t hat the two theories are related by S-duality. (C) 1997 Elsevier Scien ce B.V.