Features of the Primordial Universe in f(R)-gravity as viewed in the Jordan frame

TL;DR

This paper explores the primordial universe in f(R)-gravity within the Jordan frame, showing that near the initial singularity, Bianchi IX models lose chaotic behavior and analyzing quantum effects in Bianchi I models.

Contribution

It develops a Hamiltonian formalism in the Jordan frame for inhomogeneous cosmologies and demonstrates the suppression of chaos in Bianchi IX models when the scalar potential is negligible.

Findings

Bianchi IX cosmology is non-chaotic near the singularity under certain conditions

A Hamiltonian formalism for inhomogeneous models in the Jordan frame is constructed

Quantum analysis of Bianchi I shows the singularity persists in the wave function

Abstract

We analyze some relevant features of the primordial Universe as viewed in the Jordan frame formulation of the f(R)-gravity, especially when the potential term of the non-minimally coupled scalar field is negligible. We start formulating the Hamiltonian picture in the Jordan frame, using the 3-metric determinant as a basic variable and we outline that its conjugated momentum appears linearly only in the scalar constraint. Then, we construct the basic formalism to characterize the dynamics of a generic inhomogeneous cosmological model and specialize it in order to describe behaviors of the Bianchi Universes, both on a classical and a quantum regime. As a fundamental issue, we demonstrate that, when the potential term of the additional scalar mode is negligible near enough to the initial singularity, the Bianchi IX cosmology is no longer affected by the chaotic behavior, typical in vacuum of the standard Einsteinian dynamics. In fact, the presence of stable Kasner stability region and its actractive character are properly characterized. Finally, we investigate the canonical quantization of the Bianchi I model, using as time variable the non-minimally coupled scalar field and showing that the existence of a conserved current is outlined for the corresponding Wheeler-DeWitt equation. The behavior of a localized wave-packet for the isotropic Universe is also evolved, demonstrating that the singularity is still present in this revised quantum dynamics.