2014/04/30 by Emilio Bellini, Ignacy Sawicki · 2 citations
Physics and Astronomy · #astro-ph.CO #gr-qc
paper · pdf · doi:10.1088/1475-7516/2014/07/050
published as JCAP07(2014)050 · version accepted for publication in JCAP. Order of section 3 slightly altered. 23 pages plus appendices
arxiv created 2014/06/17 · arxiv updated 2014/07/29
We present a turnkey solution, ready for implementation in numerical codes, for the study of linear structure formation in general scalar-tensor models involving a single universally coupled scalar field. We show that the totality of cosmological information on the gravitational sector can be compressed - without any redundancy - into five independent and arbitrary functions of time only and one constant. These describe physical properties of the universe: the observable background expansion history, fractional matter density today, and four functions of time describing the properties of the dark energy. We show that two of those dark-energy property functions control the existence of anisotropic stress, the other two - dark-energy clustering, both of which are can be scale-dependent. All these properties can in principle be measured, but no information on the underlying theory of acceleration beyond this can be obtained. We present a translation between popular models of late-time acceleration (e.g. perfect fluids, f (R), kinetic gravity braiding, galileons), as well as the effective field theory framework, and our formulation. In this way, implementing this formulation numerically would give a single tool which could consistently test the majority of models of late-time acceleration heretofore proposed.