Structure of primordial gravitational waves spectrum in a double inflationary model

The gravitational waves (GW) background generated in a double inflationary model, with two scalar fields mutually interacting through gravity only, and its relative contribution TS to large-angle temperature fluctuations of the relic microwave background are investigated in detail. The relation between TS and the slope of the GW spectrum nT 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.