Closed strings from nothing - art. no. 066002

We study the physics of open strings in bosonic and type-II string theories in the presence of unstable D-branes. When the potential energy of the ope n string tachyon is at its minimum. Sen has argued that only closed strings remain in the perturbative spectrum. We explore the scenario of Yi and of Bergman, Hori. and Yi. who argue that the open string degrees of freedom ar e strongly coupled and disappear through confinement. We discuss arguments using open string field theory and world sheet boundary renormalization gro up flows, which seem to indicate otherwise. We then describe a solitonic ex citation of the open string tachyon and gauge field with the charge and ten sion of a fundamental closed string. This requires a double scaling limit w here the tachyon is taken to its minimal value and the electric field is ta ken to its maximum value. The resulting flux tube has an unconstrained spat ial profiled and for large fundamental string charge it appears to have lig ht, weakly coupled open strings existing in the core. We argue that the flu x tube acquires a size of order alpha' through sigma model and string coupl ing effects, and that confinement effects make the light degrees of freedom heavy and strongly interacting.