Phenomenology of interacting gravitational waves during inflation

Detection of tensor mode fluctuations at the largest cosmological scales is often expected to provide a robust evidence of inflation and to fix the inflationary energy scale. Such direct connection is however applicable only when gravitational waves (GWs), the source of tensor perturbations, are effectively decoupled from other energy contents. In this talk I discuss a case exceptional to this standard lore. Spin-1 particles can be produced efficiently during inflation due to interactions, and their energy is then transferred to GWs. When a spin-1 field has homogeneous part with a configuration, produced particles can source GWs to the amount considerably larger than the standard amplitude. Moreover, such GWs have non-trivial correlations with curvature perturbations, leading to interesting cross correlation functions, which would otherwise be absent. I demonstrate detectable GW signals even from low-energy inflation and discuss potentially observable correlations between tensor and scalar perturbations.