Unstable D-branes and string cosmology

Abstract

The cosmological implications of rolling tachyons are reported in the context of effective field theory. With a brief review of rolling tachyons in both flat and curved spacetimes, we study the string cosmological model with both tachyon and dilaton. In the string frame, flat space solutions of both initial-stage and late-time are obtained in closed form. In the Einstein frame, every expanding solution is decelerating. When a Born-Infeld U(1) gauge field is coupled, enhancement of the e-folding of the scale factor is also discussed by numerical analysis.