Inflation from inhomogeneous polarized Gowdy model

TL;DR

This paper analyzes polarized Gowdy cosmologies with a massive scalar field, revealing regimes where inhomogeneities evolve linearly and can lead to an early universe that isotropizes and homogenizes over time.

Contribution

It introduces a framework for understanding nonperturbative inhomogeneities in Gowdy models with a massive scalar field, identifying conditions for linear dynamics and late-time isotropization.

Findings

Inhomogeneous fields can be expressed as linear combinations of solutions with conserved coefficients.

The model describes a universe transitioning from an inhomogeneous, kinetically dominated phase to a slow-roll, nearly exponential expansion.

Constants of motion are identified for the Fourier modes of inhomogeneities.

Abstract

We study polarized Gowdy cosmologies on the three torus coupled to a massive scalar field. The phase space of the model admits a simple splitting between homogeneous and inhomogeneous sectors after a suitable gauge fixing. The presence of the mass term of the scalar field breaks the linearity of the equations of motion of the inhomogeneous fields. We discuss regimes of physical interest in which we recover a linear dynamics of these nonperturbative inhomogeneities, despite the metric is fully inhomogeneous at early times. We expand the inhomogeneous fields in Fourier modes and express them at all times as linear combinations of a basis of orthonormal complex solutions to the equations of motion, with coefficients that turn out to be an infinite collection of constants of motion. We argue that the resulting model can describe a nonperturbative inhomogeneous early universe dominated by the kinetic energy of an inflaton at early times that can eventually reach a slow-roll regime with a nearly exponential expansion at late times that isotropices and homogenizes the geometry.