Inflationary attractors and perturbation spectra in generally coupled gravity

A generic outcome of theories with scalar-tensor coupling is the existence of inflationary attractors, either power law or de Sitter type. The fluctuations arising during this phase are Gaussian and their spectrum depends on the wave number $k$ according to the power law $k^{\frac{1}{\mathrm{}(1-p)\mathrm{}}}$, where $p$ is the inflationary power-law exponent. We investigate to what extent these properties depend on the coupling function and potential. We find the class of models in which variable 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 Gaussian behavior are negligible.