Sound speed of scalar field dark energy: weak effects and large uncertainties

TL;DR

This paper investigates the reconstruction of scalar field dark energy parameters, including sound speed, using diverse cosmological data, and finds that current data do not favor any specific sound speed value due to weak effects on observable structures.

Contribution

It provides a comprehensive analysis of dark energy sound speed estimation and demonstrates the weak influence of dark energy perturbations on cosmological observations.

Findings

No preferred dark energy sound speed in [0,1] range.

Dark energy perturbations have minimal impact on large-scale structure.

Reconstruction of scalar field parameters is feasible up to an arbitrary constant.

Abstract

The possibility of reconstruction of Lagrangian for the scalar field dark energy with constant effective sound speed $c_s$ is analyzed. It is found that such reconstruction can be made with accuracy up to an arbitrary constant. The value of $c_s$ is estimated together with other dark energy parameters ($\Omega_{de}$, $w_0$, $c_a^2$) and main cosmological ones on the basis of data including Planck-2013 results on CMB anisotropy, BAO distance ratios from recent galaxy surveys, galaxy power spectrum from WiggleZ, magnitude-redshift relations for distant SNe Ia from SNLS3 and Union2.1 compilations, the HST determination of the Hubble constant. It is shown that no value of $c_s$ from the range [0,1] is preferred by the used data because of very weak influence of dark energy perturbations on the large scale structure formation and CMB temperature fluctuations.