A Galileon Design of Slow Expansion

TL;DR

This paper proposes a slow expansion model using a generalized Galileon field that generates a scale-invariant curvature perturbation spectrum without ghost instabilities, offering a new approach to early universe cosmology.

Contribution

It introduces a novel Galileon-based slow expansion scenario that produces scale-invariant perturbations with a healthy perturbation theory, avoiding ghost instabilities.

Findings

The model achieves a scale-invariant spectrum via increasing mode during slow expansion.

It remains free of ghost instabilities and maintains healthy perturbation theory.

The universe reheats after the slow expansion phase ends.

Abstract

We show a model of the slow expansion, in which the scale invariant spectrum of curvature perturbation is adiabatically induced by its increasing mode, by applying a generalized Galileon field. In this model, initially \epsilon << -1, which then is rapidly increasing, during this period the universe is slowly expanding. There is not the ghost instability, the perturbation theory is healthy. When \epsilon \sim -1, the slow expansion phase ends, and the available energy of field can be released and the universe reheats. This scenario might be a viable design of the early universe.