  The cosmological background of gravitational waves can be tuned by the
higher-order corrections to the gravitational Lagrangian. In particular, it can
be shown that assuming $R^{1+\epsilon}$, where $\epsilon$ indicates a generic
(eventually small) correction to the Hilbert-Einstein action in the Ricci
scalar $R$, gives a parametric approach to control the evolution and the
production mechanism of gravitational waves in the early Universe.
