Inflationary Attractors and Perturbation Spectra in Generally Coupled Gravity

TL;DR

This paper explores inflationary attractors in scalar-tensor gravity theories, showing that certain properties like fluctuation spectra are robust against variations in coupling functions, with negligible non-Gaussian deviations.

Contribution

It identifies classes of models with viable attractors where cosmic expansion and fluctuation spectra are independent of coupling functions.

Findings

Inflationary attractors include power-law and de Sitter solutions.

Fluctuation spectra follow a power-law dependence on wavenumber.

Deviations from Gaussianity are negligible in these models.

Abstract

A generic outcome of theories with scalar-tensor coupling is the existence of inflationary attractors, either power-law or de Sitter. The fluctuations arising during this phase are Gaussian and their spectrum depends on the wavenumber $k$ according to the power-law $k^{1/(1-p)}$, where $p$ is the inflationary power-law exponent. We investigate to which extent these properties depend on the coupling function and on the potential. We find the class of models in which viable attractors exist. Within this class, we find that the cosmic expansion and the scaling of the fluctuation spectrum are independent of the coupling function. Further, the analytical solution of the Fokker-Planck equation shows that the deviations from Gaussianity are negligible.