  The gravitational waves (GW) background generated in a double inflationary
model, with two scalar fields mutually interacting through gravity only, and
its relative contribution $T/S$ to large-angle temperature fluctuations of the
relic microwave background are investigated in detail. The relation between
$T/S$ and the slope of the GW spectrum $n_T$ is shown to be a discriminative
test between a slow-roll inflation driven by one scalar field and more
complicated models. It is found that the GW amplitude is not exactly zero in
minima of spectral oscillations, this property being an observational, in
principle, manifestation of GW being in a squeezed vacuum state during
inflation.
