Future CMB Constraints on Early, Cold, or Stressed Dark Energy

TL;DR

This paper assesses how future CMB experiments can constrain early dark energy, considering clustering and anisotropic stresses, and examines impacts on neutrino mass measurements.

Contribution

It introduces a comprehensive analysis of EDE constraints including clustering and anisotropic stresses, highlighting degeneracies and biases affecting parameter estimation.

Findings

Anisotropic stresses significantly affect EDE sound speed constraints.

Future CMB experiments can tightly constrain EDE primordial energy density.

Neglecting EDE leads to biased neutrino mass estimates.

Abstract

We investigate future constraints on early dark energy (EDE) achievable by the Planck and CMBPol experiments, including cosmic microwave background (CMB) lensing. For the dark energy, we include the possibility of clustering through a sound speed c_s^2 <1 (cold dark energy) and anisotropic stresses parameterized with a viscosity parameter c_vis^2. We discuss the degeneracies between cosmological parameters and EDE parameters. In particular we show that the presence of anisotropic stresses in EDE models can substantially undermine the determination of the EDE sound speed parameter c_s^2. The constraints on EDE primordial energy density are however unaffected. We also calculate the future CMB constraints on neutrino masses and find that they are weakened by a factor of 2 when allowing for the presence of EDE, and highly biased if it is incorrectly ignored.