# Curvature and isocurvature perturbations in two-field inflation

## TL;DR

This paper analyzes the evolution of curvature and isocurvature perturbations during two-field inflation with non-standard kinetic terms, combining analytical and numerical methods to understand their impact on cosmological observables.

## Contribution

It provides analytical expressions for perturbation spectra at Hubble crossing and demonstrates how isocurvature modes influence curvature perturbations during inflation.

## Key findings

- Isocurvature perturbations significantly affect curvature perturbations.
- Analytical spectra are derived up to first order in slow-roll parameters.
- Numerical simulations confirm the impact of isocurvature modes in specific models.

## Abstract

We study cosmological perturbations in two-field inflation, allowing for non-standard kinetic terms. We calculate analytically the spectra of curvature and isocurvature modes at Hubble crossing, up to first order in the slow-roll parameters. We also compute numerically the evolution of the curvature and isocurvature modes from well within the Hubble radius until the end of inflation. We show explicitly for a few examples, including the recently proposed model of `roulette' inflation, how isocurvature perturbations affect significantly the curvature perturbation between Hubble crossing and the end of inflation.