Bouncing universe and non-BPS branes
  We describe string frame bouncing universe scenarios involving the creation
and annihilation of a non-BPS D9-brane in type IIA superstring theory. We find
several classes of solutions, in which the bounce is driven by the tachyon
dynamics of the non-BPS brane. The metric and the dilaton are consistently
described in terms of the lowest order effective action. The bounce solutions
interpolate between contracting and expanding pre-big bang (or post-big bang)
solutions. The singular behavior of our bounce solutions is the same as that of
the pre-big bang (or post-big bang) solution. Upon adding a simple dilaton
potential the asymptotic curvature singularity is removed but the dilaton still
grows without bound. Such a potential may result from $\alpha'$ corrections in
the open string sector.
