Toy models for closed string tachyon solitons

We present qualitative evidence that closed string tachyon solitons describe backgrounds of lower-dimensional sub-critical string theory. We show that a co-dimension one soliton in the low energy effective gravity-dilaton-tachyon theory in general has a flat string-frame metric, and a dilaton that grows in both directions away from the core, and is linear in the soliton worldvolume coordinates. Spacetime, as seen in the Einstein frame, is therefore effectively localized in (D-1)-dimensions, in which the dilaton is linear, in agreement with the linear dilaton background of the (D-1)-dimensional sub-critical string. We construct a number of exactly solvable toy models with specific tachyon potentials that exhibit these features, and address the question of finding solitons in the bosonic closed string field theory using the recent advances in computing the tachyon potential.