Modified FRW cosmologies arising from states of the hybrid quantum Gowdy model

TL;DR

This paper develops approximate solutions in hybrid quantum Gowdy cosmology, showing how complex inhomogeneous models can be effectively described by simpler homogeneous and isotropic cosmologies with modified gravity features.

Contribution

It introduces a method to approximate the Gowdy model's Hamiltonian constraint with a simpler one, linking inhomogeneous quantum states to effective homogeneous cosmologies.

Findings

Quantum states exhibit correlations enabling simplified dynamics.

Approximate solutions resemble flat FRW universes with modified gravity terms.

Inhomogeneous quantum states can be effectively described by homogeneous models.

Abstract

We construct approximate solutions of the hybrid quantum Gowdy cosmology with three-torus topology, linear polarization, and local rotational symmetry, in the presence of a massless scalar field. More specifically, we determine some families of states for which the complicated inhomogeneous and anisotropic Hamiltonian constraint operator of the Gowdy model is approximated by a much simpler one. Our quantum states follow the dynamics governed by this simpler constraint, while being at the same time also approximate solutions of the full Gowdy model. This is so thanks to the quantum correlations that the considered states present between the isotropic and anisotropic sectors of the model. Remarkably, this simpler constraint can be regarded as that of a flat Friedmann-Robertson-Walker universe filled with different kinds of perfect fluids and geometrically corrected by homogeneous and isotropic curvature-like terms. Therefore, our quantum states, which are intrinsically inhomogeneous, admit approximate homogeneous and isotropic effective descriptions similar to those considered in modified theories of gravity.