Primordial non-Gaussianity from Galilean Genesis without strong coupling problem

TL;DR

This paper examines Galilean Genesis models that avoid strong coupling issues and assesses their ability to explain CMB fluctuations, finding a trade-off with excessive scalar non-Gaussianity.

Contribution

It investigates the viability of strong coupling-free Galilean Genesis models in explaining CMB features within specific propagation speed frameworks.

Findings

Models without strong coupling produce too much scalar non-Gaussianity.

Constant propagation speeds simplify the analysis of perturbations.

Red-tilted spectra in these models lead to overproduction of non-Gaussianity.

Abstract

Galilean Genesis is generically plagued with a strong coupling problem, but this can be avoided depending on the hierarchy between a classical energy scale of genesis and a strong coupling scale. In this paper, we investigate whether or not the models of Galilean Genesis without the strong coupling problem can explain the statistical properties of the observed CMB fluctuations based on two unified frameworks of Galilean Genesis. By focusing on the class in which the propagation speeds of the scalar and tensor perturbations are constant, we show that the models avoiding strong coupling and allowing a slightly red-tilted scalar power spectrum suffer from an overproduction of a scalar non-Gaussianity.