On the phase transition to spacetime in string cosmology

Closed string models have recently been constructed in lower than their critical spacetime dimensions D {=} 4 undergoes a phase transition at a universal point (Hagedorn temperature). The authors argue that solitonic configurations on the string world-sheet (vortices) drive the system into a high-temperature phase where the vacuum is dominated by vortex condensates. Flat spacetime is identified with the dipole low-temperature phase of vortex antivortex pairs. This is a Kosterlitz-Thouless transition on the string world-sheet. It is suggestive of a stringy realization of the inflationary universe paradigm.