Angular inflation in multi-field ${\alpha}$-attractors

TL;DR

This paper investigates multi-field $ ext{alpha}$-attractor inflation models with hyperbolic field-space, discovering a new angular inflation attractor that influences observable predictions, especially in highly curved scenarios.

Contribution

It introduces the concept of angular inflation as a novel multi-field attractor in hyperbolic field-space models and analyzes its impact on inflationary predictions.

Findings

Angular inflation is a new dynamical attractor along the boundary of the Poincare disc.

Isocurvature modes decay during angular inflation, affecting perturbation evolution.

High curvature can lead to predictions outside current observational bounds.

Abstract

We explore the dynamics of multi-field models of inflation in which the field-space metric is a hyperbolic manifold of constant curvature. Such models are known as $\alpha$-attractors and their single-field regimes have been extensively studied in the context of inflation and supergravity. We find a variety of multi-field inflationary trajectories in different regions of parameter space, which is spanned by the mass parameters and the hyperbolic curvature. Amongst these is a novel dynamical attractor along the boundary of the Poincare disc which we dub "angular inflation". We calculate the evolution of adiabatic and isocurvature fluctuations during this regime and show that, while isocurvature modes decay during this phase, the duration of the angular inflation period can shift the single-field predictions of $\alpha$-attractors. For highly curved field-space manifolds, this can lead to predictions that lie outside the current observational bounds.