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 description of a pair of "stuck" D0-branes in an orientifold compactification 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 strength *F-10, evidence for a -2-brane in the BPS spectrum of M-theory. Using heterotic-type I duality, we infer the existence of an M2-brane of finite width 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 heterotic string. This phenomenon has a bosonic string analog in the existence of a stable short electric flux tube arising from the confinement of photons due to tachyon Field dynamics. The appendix clarifies the appearance of nonperturbative states and enhanced gauge symmetry in toroidal compactifications of the type I' string. We account for all of the known disconnected components of the moduli space of theories with sixteen supercharges, in striking confirmation of heterotic-type I duality. (C) 2000 Elsevier Science B.V. All rights reserved.