Born-Again Braneworld

We propose a cosmological braneworld scenario in which two branes collide andemerge as reborn branes whose tensions have signs opposite to the originaltensions of the respective branes. In this scenario, gravity on each of thebranes is described by a scalar-tensor-type theory in which the radion playsthe role of the gravitational scalar, and the branes are assumed to beinflating. However, the whole dynamics is different from those of the usualinflation, due to the non-trivial dynamics of the radion field. Transformingthe conformal frame to the Einstein frame, this born-again scenario resemblesthe pre-big-bang scenario. Thus, our scenario has features of both inflationand pre-big-bang scenarios. In particular, gravitational waves produced fromvacuum fluctuations may have a very blue spectrum, while the inflaton fieldgives rise to a standard scale-invariant spectrum.Comment: 14 pages, 4 figures; Published version, references and minor comments adde