Nonlocal Inflation

TL;DR

This paper explores the feasibility of cosmic inflation within nonlocal field theories characterized by infinitely many derivatives, addressing stability issues and potential observational signatures like non-Gaussianity.

Contribution

It provides a comprehensive analysis of the dynamics, stability, and phenomenology of nonlocal inflation models derived from string theory and related toy models.

Findings

Nonlocal inflation can occur with steep potentials.

Models predict large non-Gaussianity in the CMB.

Stability and initial value problems are manageable in these theories.

Abstract

We consider the possibility of realizing inflation in nonlocal field theories containing infinitely many derivatives. Such constructions arise naturally in string field theory and also in a number of toy models, such as the p-adic string. After reviewing the complications (ghosts and instabilities) that arise when working with high derivative theories we discuss the initial value problem and perturbative stability of theories with infinitely many derivatives. Next, we examine the inflationary dynamics and phenomenology of such theories. Nonlocal inflation can proceed even when the potential is naively too steep and generically predicts large nongaussianity in the Cosmic Microwave Background.