The effect of multiple features on the power spectrum in two-field inflation

Understand

We extend our previous work on the enhancement of the curvature spectrum during inflation to the two-field case.

• We identify the slow-roll parameter $\eta$ as the quantity that can trigger the rapid growth of perturbations.
• Its two components, $\eta_\parallel$ along the background trajectory and $\eta_\perp$ perpendicular to it, remain small during most of the evolution, apart from short intervals during which they take large, positive or negative, values.
• The typical reason for the appearance of strong features in $\eta_\parallel$ is sharp steps or inflection points in the inflaton potential, while $\eta_\perp$ grows large during sharp turns in field space.