Observational hints on the Big Bounce

TL;DR

This paper explores how a cosmic bounce preceding inflation, modeled via loop quantum gravity, could leave observable signatures in the cosmic microwave background, and derives constraints on model parameters from WMAP data.

Contribution

It introduces observational constraints on bouncing cosmologies with inflation, especially within loop quantum gravity, and proposes a new consistency check for slow-roll inflation.

Findings

Inflation is preceded by a bounce affecting perturbation spectra.

The inflaton mass is estimated as (2.6 ± 0.6) × 10^{13} GeV.

Current data cannot distinguish bouncing models from standard Big Bang.

Abstract

In this paper we study possible observational consequences of the bouncing cosmology. We consider a model where a phase of inflation is preceded by a cosmic bounce. While we consider in this paper only that the bounce is due to loop quantum gravity, most of the results presented here can be applied for different bouncing cosmologies. We concentrate on the scenario where the scalar field, as the result of contraction of the universe, is driven from the bottom of the potential well. The field is amplified, and finally the phase of the standard slow-roll inflation is realized. Such an evolution modifies the standard inflationary spectrum of perturbations by the additional oscillations and damping on the large scales. We extract the parameters of the model from the observations of the cosmic microwave background radiation. In particular, the value of inflaton mass is equal to $m=(2.6 \pm 0.6) \cdot 10^{13}$ GeV. In our considerations we base on the seven years of observations made by the WMAP satellite. We propose the new observational consistency check for the phase of slow-roll inflation. We investigate the conditions which have to be fulfilled to make the observations of the Big Bounce effects possible. We translate them to the requirements on the parameters of the model and then put the observational constraints on the model. Based on assumption usually made in loop quantum cosmology, the Barbero-Immirzi parameter was shown to be constrained by $\gamma<1100$ from the cosmological observations. We have compared the Big Bounce model with the standard Big Bang scenario and showed that the present observational data is not informative enough to distinguish these models.