Large N Cosmology

TL;DR

This paper explores inflationary models with many scalar fields, providing a comprehensive framework for analyzing adiabatic and entropy perturbations without relying on slow roll or SO(N) symmetry, and highlights how multi-field effects alter fluctuation spectra.

Contribution

It offers a complete formulation for perturbations in multi-field inflation, applicable even without slow roll or SO(N) symmetry, simplifying spectrum calculations to two variables.

Findings

Spectrum calculation simplifies to two variables under certain symmetries.

Multi-field inflation can produce different fluctuation spectra than single-field models.

The framework applies broadly without assuming slow roll or specific symmetries.

Abstract

We motivate inflationary scenarios with many scalar fields, and give a complete formulation of adiabatic and entropy perturbations. We find that if the potential is very flat, or if the theory has a SO(N) symmetry, the calculation of the fluctuation spectrum can be carried out in terms of merely two variables without any further assumption. We do not have to assume slow roll or SO(N) invariance for the background fields. We give some examples to show that, even if the slow roll assumption holds, the spectrum of fluctuations can be quite different from the case when there is a single inflaton.