Ekpyrotic Cosmology with a Zero-Shear S-Brane

Understand

In a recent paper we proposed a mechanism for a continuous transition between a contracting Ekpyrotic phase and the Standard Big Bang phase of expansion: the bounce is generated by an S-brane which represents the effects of higher mass string states in the low energy effective field theory.

• We showed that gravitational waves on cosmological scales obtain a nearly scale-invariant spectrum.
• Here, we study the cosmological fluctuations in this setup, assuming that the S-brane has zero shear.
• We find a nearly scale-invariant spectrum of cosmological perturbations with a slight red tilt.