Chennai Mathematical Institute


11.00 am, Seminar Hall
Viable scalar spectral tilt and tensor-to-scalar ratio in near-matter bounces

L. Sriram Kumar
IIT Madras.


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 symmetric bounces that lead to primordial spectra that are consistent with the cosmological data. In this talk, I describe a model involving two scalar fields (a canonical field and a non-canonical ghost field) that drive symmetric near-matter bounces and discuss the evolution of the scalar and tensor perturbations in the model. The model can be completely described in terms of two parameters, one which is the ratio of the scale associated with the bounce to the value of the scale factor at the bounce and another that characterizes the extent of deviation from the matter bounce. We evolve the scalar perturbations numerically across the bounce and evaluate the scalar and tensor power spectra after the bounce. When feasible, we also support our numerical results with analytical arguments. We show that, for suitable values of the parameters, the model leads to a scalar spectral tilt and a tensor-to-scalar ratio that are in agreement with the data from the observations of the cosmic microwave background anisotropies by the Planck mission. We close by highlighting the typical challenges faced in constructing viable bouncing scenarios.