Inflation as an attractor in scalar cosmology

TL;DR

This paper explores how attractor solutions in scalar field cosmology can lead to eternal inflation, providing a new Hamilton-Jacobi approach and analyzing stability conditions for different potentials.

Contribution

It introduces a novel method to solve the Hamilton-Jacobi equation in scalar cosmology and characterizes conditions for attractor and quasi-attractor solutions.

Findings

Attractor solutions lead to eternal inflation driven by positive potential energy.

Existence of attractors depends on the form of the scalar potential, especially the absence of linear and quadratic terms.

Quasi-attractors occur under certain conditions but are sensitive to potential modifications.

Abstract

We study an inflation mechanism based on attractor properties in cosmological evolutions of a spatially flat Friedmann-Robertson-Walker spacetime based on the Einstein-scalar field theory. We find a new way to get the Hamilton-Jacobi equation solving the field equations. The equation relates a solution `generating function' with the scalar potential. We analyze its stability and find a later time attractor which describes a Universe approaching to an eternal-de Sitter inflation driven by the potential energy, $V_0>0$. The attractor exists when the potential is regular and does not have a linear and quadratic terms of the field. When the potential has a mass term, the attractor exists if the scalar field is in a symmetric phase and is weakly coupled, $\lambda<9V_0/16$. We also find that the attractor property is intact under small modifications of the potential. If the scalar field has a positive mass-squared or is strongly coupled, there exists a quasi-attractor. However, the quasi-attractor property disappears if the potential is modified. On the whole, the appearance of the eternal inflation is not rare in scalar cosmology in the presence of an attractor.