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167. The return of the phoenix universe
This is a guest blog post by Jean-Luc Lehners from Princeton University. Dmitry.
In a recent paper entitled “Dark energy and the return of the phoenix universe” that I wrote with Paul Steinhardt, we analyzed the fate and global structure of the two-scalar-field cyclic universe. (In the cyclic universe the big bang is modeled by the regular collision of two end-of-the-world branes, see section 5 of my review.) From the point of view of string theory, this is a natural model to consider, as there always are two scalar fields in braneworld models: one parameterizing the distance between the two branes, and one determining the volume of the internal space. Of course there could be many more such moduli, but this is the minimal model. From the point of view of cosmology, this model constitutes a rather nice setup, as it allows the density perturbations to arise via the entropic mechanism, in which nearly scale-invariant entropy perturbations are produced first, and these are then converted into adiabatic perturbations just before the big crunch.
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