Fingerprinting Dark Energy III: distinctive marks of viscosity

Abstract

The characterisation of dark energy is one of the primary goals in cosmology especially now that many new experiments are being planned with the aim of reaching a high sensitivity on cosmological parameters. It is known that if we move away from the simple cosmological constant model then we need to consider perturbations in the dark energy fluid. This means that dark energy has two extra degrees of freedom: the sound speed $\cs$ and the anisotropic stress $\sigma$. If dark energy is inhomogenous at the scales of interest then the gravitational potentials are modified and the evolution of the dark matter perturbations is also directly affected. In this paper we add an anisotropic component to the dark energy perturbations. Following the idea introduced in \cite{Sapone:2009mb}, we solve analytically the equations of perturbations in the dark sector, finding simple and accurate approximated solutions. We also find that the evolution of the density perturbations is governed by an effective sound speed which depends on both the sound speed and the anisotropic stress parameter. We then use these solutions to look at the impact of the dark energy perturbations on the matter power spectrum and on the Integrated Sachs-Wolfe effect in the Cosmic Microwave Background.

14 pages, 8 figures, to be submitted to PRD

References in corpus (14)

• Dynamics of dark energy
• Measuring the dark side (with weak lensing)
• Dark Energy versus Modified Gravity
• How to optimally parametrize deviations from General Relativity in the evolution of cosmological perturbations
• The Case for Dark Radiation
• Crossing the Phantom Divide
• Constraining Dark Energy Anisotropic Stress
• Fingerprinting dark energy
• Future CMB Constraints on Early, Cold, or Stressed Dark Energy
• Dark Energy in Practice
• Fingerprinting Dark Energy II: weak lensing and galaxy clustering tests
• New Parametrization for the Scale Dependent Growth Function in General Relativity
• A new perspective on the relation between dark energy perturbations and the late-time ISW effect
• Constraining modified growth patterns with tomographic surveys

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