Cosmological unification of string theories

TL;DR

This paper constructs an exact time-dependent solution in superstring theory that smoothly transitions from an initial type 0 phase to a final bosonic string phase, demonstrating a dynamic unification of string theories.

Contribution

It provides the first explicit, exact solution showing how superstring theory can dynamically evolve into bosonic string theory via tachyon condensation.

Findings

Demonstrates a smooth, exact interpolation between superstring and bosonic string phases.

Shows the role of lightlike tachyon condensation in connecting different string theories.

Provides a concrete realization of the Berkovits-Vafa embedding in a time-dependent setting.

Abstract

We present an exact solution of superstring theory that interpolates in time between an initial type 0 phase and a final phase whose physics is exactly that of the bosonic string. The initial theory is deformed by closed-string tachyon condensation along a lightlike direction. In the limit of large tachyon vev, the worldsheet conformal field theory precisely realizes the Berkovits-Vafa embedding of bosonic string theory into superstring theory. Our solution therefore connects the bosonic string dynamically with the superstring, settling a longstanding question about the relationship between the two theories.