We check some consistency conditions for the D9-D9 system in type I string theory. The gravitational anomaly and gauge anomaly for SO(n) × SO(m) gauge symmetry are shown to be cancelled when n − m = 32. In addition, we find that a string theory with USp(n) × USp(m) gauge symmetry also satisfies the anomaly cancellation conditions. After tachyon condensation, the theory reduces to a tachyon-free USp(32) string theory, though there is no spacetime supersymmetry.
No takes yet. Share an insight, caveat, or question.
A 1999 study studied this question.