Running of scalar spectral index in multi-field inflation

TL;DR

This paper calculates the running of the scalar spectral index in multi-field slow-roll inflation, explicitly considering momentum dependence at horizon crossing to differentiate background and super-horizon effects.

Contribution

It introduces a method to compute the spectral index running in multi-field inflation by explicitly including momentum dependence at horizon crossing.

Findings

Provides a straightforward calculation of spectral index running.

Distinguishes contributions from background and super-horizon evolution.

Enhances understanding of multi-field inflation dynamics.

Abstract

We compute the running of the scalar spectral index in general multi-field slow-roll inflation. By incorporating explicit momentum dependence at the moment of horizon crossing, we can find the running straightforwardly. At the same time, we can distinguish the contributions from the quasi de Sitter background and the super-horizon evolution of the field fluctuations.