Parameterizing dark sector perturbations via equations of state

Abstract

The evolution of perturbations is a crucial part of the phenomenology of the dark sector cosmology. We advocate parameterizing these perturbations using equations of state for the entropy perturbation and the anisotropic stress. For small perturbations, these equations of state will be linear in the density, velocity and metric perturbations, and in principle these can be related back to the field content of the underlying model allowing for confrontation with observations. We illustrate our point by constructing gauge invariant entropy perturbations for theories where the dark sector Lagrangian is a general function of a scalar field, its first and second derivatives, and the metric and its first derivative, $\mathcal{L}=\mathcal{L}(\varphi ,{\partial }_{\mu }\varphi ,{\partial }_{\mu }{\partial }_{\nu }\varphi ,g_{\mu \nu },{\partial }_{\alpha }{g}_{\mu \nu })$. As an example, we show how to apply this approach to the case of models of Kinetic Gravity Braiding.

4 pages; typos corrected; matches published version

References in corpus (13)

• Dynamics of dark energy
• Imperfect Dark Energy from Kinetic Gravity Braiding
• Starting the Universe: Stable Violation of the Null Energy Condition and Non-standard Cosmologies
• Dark Energy or Modified Gravity? An Effective Field Theory Approach
• The Effective Theory of Quintessence: the w<-1 Side Unveiled
• Current constraints on the cosmic growth history
• The Parameterized Post-Friedmann Framework for Theories of Modified Gravity: Concepts, Formalism and Examples
• A practical approach to cosmological perturbations in modified gravity
• Constraints on a New Post-General Relativity Cosmological Parameter
• Examining the evidence for dynamical dark energy
• Parametrized Post-Friedmann Signatures of Acceleration in the CMB
• Consistent perturbations in an imperfect fluid
• Cosmological Perturbations in Elastic Dark Energy Models

Cited by in corpus (33)

• Testing General Relativity with Present and Future Astrophysical Observations
• Beyond the Cosmological Standard Model
• Cosmological Tests of Modified Gravity
• Testing General Relativity in Cosmology
• Maximal freedom at minimum cost: linear large-scale structure in general modifications of gravity
• A unifying description of dark energy
• Growth of Cosmic Structure: Probing Dark Energy Beyond Expansion
• CMB lensing tomography with the DES Science Verification galaxies
• The Novel Probes Project -- Tests of Gravity on Astrophysical Scales
• A comparison of Einstein-Boltzmann solvers for testing General Relativity
• Gravitational wave constraints on dark sector models
• Parameterized Post-Newtonian Cosmology
• Microphysics of Early Dark Energy
• The Parametrized Post-Newtonian-Vainshteinian Formalism
• f(R) as a dark energy fluid
• Investigating scalar-tensor-gravity with statistics of the cosmic large-scale structure
• Cosmological perturbation theory in Generalized Einstein-Aether models
• Computing model independent perturbations in dark energy and modified gravity
• Comparison of different approaches to the quasi-static approximation in Horndeski models
• Do cosmological data rule out $f(\mathcal{R})$ with $w\ne -1$?
• Parametrizing theories of gravity on large and small scales in cosmology
• Observable physical modes of modified gravity
• Cosmologically viable generalized Einstein-Aether theories
• Constraining dark sector perturbations I: cosmic shear and CMB lensing
• Constraining dark sector perturbations II: ISW and CMB lensing tomography
• Dark sector evolution in Horndeski models
• The Parameterized Post-Newtonian-Vainshteinian formalism for the Galileon field
• Simple numerical implementation of general dark energy models
• Matter Growth in Imperfect Fluid Cosmology
• On (non-)dynamical dark energy
• Post-Newtonian Gravity in Cosmology
• Matter growth in extended $\Lambda$CDM cosmology
• The Equation of State Approach to Cosmological Perturbations in f(R) Gravity