Confinement and the short type I ' flux tube

We show that the recent worldsheet analysis of the: quantum fluctuations of a short flux tube in type II string theory leads to a simple and precise d escription of a pair of "stuck" D0-branes in an orientifold compactificatio n of the type I' string theory. The existence of a stable type I' flux tube of substring-scale length is a consequence of the confinement of quantized flux associated with the scalar dualized ten-form background field strengt h *F-10, evidence for a -2-brane in the BPS spectrum of M-theory. Using het erotic-type I duality, we infer the existence of an M2-brane of finite widt h O(root alpha') in M-theory, the strong coupling resolution of a spacetime singularity in the D = 9 twisted and toroidally compactified E-8 x E-8 het erotic string. This phenomenon has a bosonic string analog in the existence of a stable short electric flux tube arising from the confinement of photo ns due to tachyon Field dynamics. The appendix clarifies the appearance of nonperturbative states and enhanced gauge symmetry in toroidal compactifica tions of the type I' string. We account for all of the known disconnected c omponents of the moduli space of theories with sixteen supercharges, in str iking confirmation of heterotic-type I duality. (C) 2000 Elsevier Science B .V. All rights reserved.