Large tensor-to-scalar ratio and low scale inflation

Understand

It is plausible that the scalar density perturbations are created by a relatively low scale model of inflation which predicts the CMB anisotropy and excites Standard Model baryon and cold dark matter, but negligible gravity waves.

• Nevertheless a significantly large tensor perturbations can be observed if there exists a prior phase of high scale inflation separated by a matter or radiation dominated epoch.
• In this paper we provide a simple example when the gravity waves generated at high scales trickle through the horizon of the second phase of inflation and leave a distinct imprint in the spectrum of the tensor modes.
• For a high scale inflation occurring at $H\sim 10^{13}$ GeV while the second phase of inflation happening at $H\sim 1$ GeV, the largest tensor to scalar ratio is bounded by $r_{\rm observed}\leq0.8$.