Curvature perturbations from kinetic preheating after $\alpha$-attractor inflation

TL;DR

This study uses high-precision lattice simulations to investigate the conversion of isocurvature to curvature perturbations during kinetic preheating after $ ext{alpha}$-attractor inflation, finding the process to be highly inefficient and observationally negligible.

Contribution

The paper provides the first detailed lattice simulation analysis of kinetic preheating in $ ext{alpha}$-attractor inflation, highlighting the inefficiency of isocurvature to curvature perturbation conversion.

Findings

Conversion from isocurvature to curvature perturbations is very inefficient.

The process is unlikely to produce detectable signals in cosmological observations.

The effective mass suppression during inflation affects preheating dynamics.

Abstract

Preheating at the end of inflation is a violent nonlinear process that efficiently transfers the energy of the inflaton to a second field, the preheat field. When the preheat field is light during inflation and its background value modulates the preheating process, the superhorizon isocurvature perturbations of the preheat field may be converted to curvature perturbations that leave an imprint on the cosmic microwave background and the large-scale structure of the universe. We use high-precision lattice simulations to study kinetic preheating after $\alpha$-attractor inflation, a case where the effective mass of the preheat field is naturally suppressed during inflation. By comparing the expansion e-folds between different Hubble patches, we find that the conversion from isocurvature perturbations to curvature perturbations is very inefficient and can hardly be detected by cosmological observations.