HEP Theory Journal Club

Gravitational waves from low-energy inflation by particle production

Ryo Namba

McGill

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 the tensor perturbations are effectively decoupled from other energy contents. In this talk I present a case exceptional to this starndard lore. When an SU(2) gauge field is present and is prevented from diluting away by a coupling to a pseudo-scalar field, the SU(2) perturbations can be amplified exponentially through the same coupling. Their produced energy is then transferred to the metric tensor modes already at the linearized level. While these fields are energetically subdominant to the inflaton, their perturbations can be considerably larger than the standard amplitude. I will discuss several potential constraints on the mechanism and demonstrate that detectable tensor-mode signals even for low-energy inflation.