Scale-Invariant Fluctuations from Galilean Genesis

TL;DR

This paper investigates the generation of scale-invariant cosmological fluctuations in Galilean Genesis scenarios, showing how higher-dimensional operators can produce Gaussian, scale-invariant curvature perturbations.

Contribution

It demonstrates that including higher-dimensional operators induces a linear coupling, resulting in scale-invariant, Gaussian fluctuations in Galilean Genesis models.

Findings

Higher-dimensional operators enable scale-invariant fluctuations.

Linear coupling leads to Gaussian curvature perturbations.

Minimal coupling yields non-scale-invariant, non-Gaussian fluctuations.

Abstract

We study the spectrum of cosmological fluctuations in scenarios such as Galilean Genesis in which a spectator scalar field acquires a scale-invariant spectrum of perturbations during an early phase which asymptotes in the far past to Minkowski space-time. In the case of minimal coupling to gravity and standard scalar field Lagrangian, the induced curvature fluctuations depend quadratically on the spectator field and are hence non-scale-invariant and highly non-Gaussian. We show that if higher dimensional operators (the same operators that lead to the {\eta}-problem for inflation) are considered, a linear coupling between background and spectator field fluctuations is induced which leads to scale-invariant and Gaussian curvature fluctuations.