Scale-invariant enhancement of gravitational waves during inflation

Understand

The inflationary 1-loop tensor power spectrum from an excited spectator scalar field is calculated.

• Recent studies on primordial black holes suggest that the inflationary curvature perturbation may be huge on small scales.
• An enhanced curvature perturbation may arise from a drastic enhancement of spectator scalar field fluctuations.
• In this letter, using the in-in formalism, we calculate 1-loop quantum corrections to primordial gravitational waves by such an excited spectator field with a sharp peak in momentum space.