  The almost scale-invariant spectrum for the stochastic background wave (in
primordial Universe) is a firm prediction of inflationary scenarios. In the
present work, to study of primordial Gravitational Waves, one dimensional toy
model in generalizations of the Einstein-Hilbert frame, described by second
order curvature invariant (called pure Quadratic Gravity) is considered.
Solutions to the primordial perturbations are more varied than Einstein-Hilbert
frame and include simple incoming and outcoming waves. By examining the
spectrum diagram of the perturbation solutions, it can be seen that the
oscillating solutions are ruled out due to not having the necessary spectral
power, but the solutions as damping exponential have the ability to produce a
scale-invariant spectrum (confirmed by CMB data).
