The bispectrum of single-field inflationary trajectories with $c_{s} \neq 1$

TL;DR

This paper investigates the bispectrum in single-field inflation models with a constant but non-unity sound speed, using numerical methods to explore a wide range of trajectories and their observational signatures.

Contribution

It introduces a numerical approach to compute bispectra for non-slow-roll, low sound speed inflationary models, extending previous methods to more general trajectories.

Findings

Distributions of bispectrum shapes and scale dependence are obtained.

Squeezed-limit consistency relations hold for arbitrary single-field models.

The method accommodates models with significant deviations from slow-roll.

Abstract

The bispectrum of single-field inflationary trajectories in which the speed of sound of the inflationary trajectories $c_s$ is constant but not equal to the speed of light $c=1$ is explored. The trajectories are generated as random realisations of the Hubble Slow-Roll (HSR) hierarchy and the bispectra are calculated using numerical techniques that extends previous work. This method allows for out-of-slow-roll models with non-trivial time dependence and arbitrarily low $c_s$. The ensembles obtained using this method yield distributions for the shape and scale-dependence of the bispectrum and their relations with the standard inflationary parameters such as scalar spectral tilt $n_s$ and tensor-to-scalar ratio $r$. The distributions demonstrate the squeezed-limit consistency relations for arbitrary single-field inflationary models.