Viable tensor-to-scalar ratio in a symmetric matter bounce

Understand

Matter bounces refer to scenarios wherein the universe contracts at early times as in a matter dominated epoch until the scale factor reaches a minimum, after which it starts expanding.

• While such scenarios are known to lead to scale invariant spectra of primordial perturbations after the bounce, the challenge has been to construct completely symmetric bounces that lead to a tensor-to-scalar ratio which is small enough to be consistent with the recent cosmological data.
• In this work, we construct a model involving two scalar fields (a canonical field and a non-canonical ghost field) to drive the symmetric matter bounce and study the evolution of the scalar perturbations in the model.
• If we consider the scale associated with the bounce to be of the order of the Planck scale, the model is completely described in terms of only one parameter, viz the value of the scale factor at the bounce.