Effects of the speed of sound at large-N

TL;DR

This paper investigates how a speed of sound less than unity during cosmic inflation affects scalar perturbations, revealing degeneracies in inflationary parameters and constraining these effects using observational bounds.

Contribution

It provides a model-independent analysis of the impact of sub-unity sound speed on inflationary observables and explores degeneracies in the parameter space.

Findings

The (n_s, r) plane shows non-trivial degeneracies with varying c_s.

Degeneracies in the running of the spectral index due to c_s are identified.

Bounds on c_s help constrain inflationary parameter degeneracies.

Abstract

The implications of a smaller than unity speed of sound of the scalar perturbations during cosmic inflation is studied in terms of a model independent large-$N$ approach. We show that the $(n_s, r)$ plane is non-trivially degenerated when the effects of a different than one speed of sound $c_s$ are taken into account. We also discuss the degeneracies due to $c_s$ in the running of the spectral index, $\alpha_s$. We use the bounds on $c_s$ to constrain such degeneracies.