Observables and unobservables in dark energy cosmologies

Abstract

The aim of this paper is to answer the following two questions: (1) Given cosmological observations of the expansion history and linear perturbations in a range of redshifts and scales as precise as is required, which of the properties of dark energy could actually be reconstructed without imposing any parameterization? (2) Are these observables sufficient to rule out not just a particular dark energy model, but the entire general class of viable models comprising a single scalar field? This paper bears both good and bad news. On one hand, we find that the goal of reconstructing dark energy models is fundamentally limited by the unobservability of the present values of the matter density Omega_m0, the perturbation normalization sigma_8 as well as the present matter power spectrum. On the other, we find that, under certain conditions, cosmological observations can nonetheless rule out the entire class of the most general single scalar-field models, i.e. those based on the Horndeski Lagrangian.

9 pages. v2 reflects version accepted for publication in PRD (includes additional discussion of geometrical distance measures, new appendix on general scalar-tensor theories and new references)

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• The phenomenological approach to modeling the dark energy
• Cosmology of the proxy theory to massive gravity
• Effective field theory of modified gravity with two scalar fields: dark energy and dark matter
• Effects of modified gravity on B-mode polarization
• Model-independent reconstruction of $f(T)$ teleparallel cosmology
• Linear growth of structure in massive bigravity
• Shaken, not stirred: kinetic mixing in scalar-tensor theories of gravity
• Model-independent limits and constraints on extended theories of gravity from cosmic reconstruction techniques
• New Gravitational Scales in Cosmological Surveys
• Observational signatures of the theories beyond Horndeski
• A cosmological exclusion plot: Towards model-independent constraints on modified gravity from current and future growth rate data
• How can we tell whether dark energy is composed by multiple fields?
• Constraining dark sector perturbations II: ISW and CMB lensing tomography
• Are Scalar and Tensor Deviations Related in Modified Gravity?
• Linear and non-linear Modified Gravity forecasts with future surveys