Probing dark energy through scale dependence

Abstract

We consider the consequences of having no prior knowledge of the true dark energy model for the interpretation of cosmological observations. The magnitude of redshift-space distortions and weaklensing shear is determined by the metric on the geodesics of which galaxies and light propagate. We show that, given precise enough observations, we can use these data to completely reconstruct the metric on our past lightcone and therefore to measure the scale-and time-dependence of the anisotropic stress and the evolution of the gravitational potentials in a model-independent manner. Since both dark matter and dark energy affect the visible sector only through the gravitational field they produce, they are inseparable without a model for dark energy: galaxy bias cannot be measured and therefore the distribution of dark matter determined; the peculiar velocity of dark matter can be identified with that of the galaxies only when the equivalence principle holds. Given these limitations, we show how one can nonetheless build tests for classes of dark energy models which depend on making measurements at multiple scales at a particular redshift. They are null tests on the model-independent observables, do not require modeling evolution in time and do not require any parametrization of the free functions of these models-such as the sound speed. We show that one in principle could rule out or constrain the whole class of the most-general scalar-tensor theories even without assuming the quasi-static limit.

Fate of Large-Scale Structure in Modified Gravity After GW170817 and GRB170817A

“…In [12,13] it was shown for the first time that a precise link between tensor and scalar fluctuations in cosmology exists: a modification to the gravitational-wave propagation at any scale implies the existence of gravitational slip (η = 1) for large-scale scalar fluctuations, with both modifications driven by exactly the same theory-space parameters of the gravitational model. The gravitational slip leaves a particular and observable imprint on the formation of structures in the universe, which can be used to constrain models of late-time acceleration [2,[14][15][16].…”

Model-independent reconstruction of the linear anisotropic stress η

“…Considering model-independent observables and linear structure formation, and assuming gravity remains universally coupled also when modified, one can build an estimate of η formed by three directly observable functions of redshift which we denote E(z), P 2 (z) and P 3 (z) (see [20]). They will be defined in detail in the following section.…”

Classifying Linearly Shielded Modified Gravity Models in Effective Field Theory

“…[21] (also see Ref. [22]) to forecast constraints on modified gravity and dark energy models using deviations introduced in the relativistic contributions to galaxy clus tering. Thereby, large-scale modifications with high-k suppression have been proposed and shown to provide measurable signatures in future galaxy-redshift surveys.…”