Non-Gaussian signatures of Tachyacoustic Cosmology

TL;DR

This paper explores non-Gaussian features in tachyacoustic cosmology, a noninflationary model with superluminal sound speed, revealing specific amplitude and shape characteristics of primordial perturbations.

Contribution

It provides the first detailed calculation of non-Gaussian signatures in tachyacoustic models, highlighting their unique amplitude and shape features compared to other superluminal models.

Findings

f_NL is of order 1 for cuscuton-like models

Non-Gaussian amplitude peaks in equilateral and local configurations

Results differ quantitatively from superluminal bimetric models

Abstract

I investigate non-Gaussian signatures in the context of tachyacoustic cosmology, that is, a noninflationary model with superluminal speed of sound. I calculate the full non-Gaussian amplitude $\mathcal{A}$, its size $f_{\rm NL}$, and corresponding shapes for a red-tilted spectrum of primordial scalar perturbations. Specifically, for cuscuton-like models I show that $f_{\rm NL}\sim {\cal O}(1)$, and the shape of its non-Gaussian amplitude peaks for both equilateral and local configurations, the latter being dominant. These results, albeit similar, are quantitatively distinct from the corresponding ones obtained by Magueijo {\it{et. al}} in the context of superluminal bimetric models.