Brane Decay and an Initial Spacelike Singularity

We present a novel string theory scenario where matter in a spacetime originates from a decaying brane at the origin of time. The decay could be considered as a big-bang-like event at $X^0=0$. The closed string interpretation is a time-dependent spacetime with a semi-infinite time direction, with the initial energy of the brane converted into energy flux from the origin. The open string interpretation can be viewed as a string theoretic nonsingular initial condition.

Figure 1

(a) The pre-big-bang (BB) scenario and (b) the creation of two universes from the big bang, which is interpreted as a spacetime $Z_2$ orbifold.

Figure 2

Brane decay on the orbifold covering space.