Hybrid Inflation with Planck Scale Fields

TL;DR

This paper explores hybrid inflation models within string-inspired modular frameworks, addressing high-scale inflation, large field excursions, and implications for axion physics, including suppression of isocurvature fluctuations.

Contribution

It proposes effective field theories for modular hybrid inflation compatible with cosmological observations and discusses their tunings and relation to chaotic inflation.

Findings

Models can achieve successful modular inflation with manageable tunings.

Axion isocurvature fluctuations can be suppressed during inflation.

Effective theories relate large field inflation to axion dynamics and symmetry breaking.

Abstract

The BICEP2 observations, if confirmed, point to a high scale of inflation and large field excursions during the inflationary era. Non-compact string moduli spaces are a suggestive setting for these phenomena. While unlikely to be described by weak coupling models, one can write down plausible effective field theories compatible with known features of cosmology. These models can be viewed as generalizations to a large field regime of hybrid inflation. We note close parallels to small and large field axion models. This paper outlines the requirements for successful modular inflation, and gives examples of effective field theories which satisfy them. The required tunings are readily characterized. These models can also be thought of as models of chaotic inflation, in a way we describe. In the modular framework, one would expect that any would-be Peccei-Quinn symmetry would likely be badly broken during inflation, and the axion would have Hubble scale mass; in this situation, isocurvature fluctuations would be suppressed and the initial misalignment angle would be fixed, rather than being a random variable.