A non-supersymmetric open-string theory and S-duality Original Research Article

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 massless tadpoles requires the gauge group to be SO(32) × SO(32). The spectrum of the theory contains a closed-string tachyon, and open-string tachyons in the (32,32) multiplet. The D-branes of this theory are analyzed, and it is found that the massless excitations of one of the 1-branes coincide with the world-sheet degrees of freedom of the D = 26 bosonic string theory compactified on the SO(32) lattice. This suggests that the two theories are related by S-duality.