Ultra slow-roll G-inflation

Understand

The conventional slow-roll approximation is broken in the so-called "ultra slow-roll" models of inflation, for which the inflaton potential is exactly (or extremely) flat.

• The interesting nature of (canonical) ultra slow-roll inflation is that the curvature perturbation grows on superhorizon scales, but has a scale-invariant power spectrum.
• We study the ultra slow-roll inflationary dynamics in the presence of non-canonical kinetic terms of the scalar field, namely ultra slow-roll G-inflation.
• We compute the evolution of the curvature perturbation and show that the primordial power spectrum follows a broken power law with an oscillation feature.