Gauge invariant perturbations of scalar-tensor cosmologies: The vacuum case

The covariant gauge-invariant perturbation theory of scalar cosmological perturbations is developed for a general scalar-tensor Friedmann-Lemaitre-Robertson-Walker cosmology in a vacuum. The perturbation equations are then solved exactly in the long wavelength limit for a specific coupling, potential, and background. Differences with the minimally coupled case are briefly discussed.

Figure 1

Plot of the solutions (85) in the inflationary regime (case $r=0.01$). The solid curve represents the $\Psi /{\Psi }_0$ the dashed one represents $\Delta /{\Psi }_0$.

Figure 2

Plot of the solutions (85) for the case $r=-5$. The solid curve represents the $\Psi /{\Psi }_0$ the dashed one represents $\Delta /{\Psi }_0$.

Figure 3

Plot of the exponent of the nonconstant mode in Eq. (87).