Symmetry Breaking Patterns for Inflation

TL;DR

This paper classifies inflationary models based on symmetry breaking patterns in the kinetic sector, introducing a new ambient inflation model with specific observational predictions related to tensor-to-scalar ratio and spectral index.

Contribution

It provides a systematic classification of inflation models by symmetry properties and introduces a novel ambient inflation model based on higher-dimensional conformal symmetries.

Findings

The ambient inflation model predicts r ~ 0.01 and n_s ~ 0.975.

Classification includes known models like monomial inflation and α-attractors.

The model involves inflation along a dilatonic direction in an anti-de Sitter space.

Abstract

We study inflationary models where the kinetic sector of the theory has a non-linearly realised symmetry which is broken by the inflationary potential. We distinguish between kinetic symmetries which non-linearly realise an internal or space-time group, and which yield a flat or curved scalar manifold. This classification leads to well-known inflationary models such as monomial inflation and $\alpha$-attractors, as well as a new model based on fixed couplings between a dilaton and many axions which non-linearly realises higher-dimensional conformal symmetries. In this model, inflation can be realised along the dilatonic direction, leading to a tensor-to-scalar ratio $r \sim 0.01$ and a spectral index $n_{s} \sim 0.975$. We refer to the new model as ambient inflation since inflation proceeds along an isometry of an anti-de Sitter ambient space-time, which fully determines the kinetic sector.