A null test to probe the scale dependence of the growth of structure as a test of general relativity
Abstract
The main science driver for the coming generation of cosmological surveys is understanding dark energy that relies on testing general relativity on the largest scales. Once we move beyond the simplest explanation for dark energy of a cosmological constant, the space of possible theories becomes both vast and extremely hard to compute realistic observables. A key discriminator of a cosmological constant, however, is that the growth of structure is scale invariant on large scales. By carefully weighting observables derived from distributions of galaxies and a dipole pattern in their apparent sizes, we construct a null test that vanishes for any model of gravity or dark energy where the growth of structure is scale independent. It relies only on very few assumptions about cosmology, and does not require any modelling of the growth of structure. We show that with a survey like the Dark Energy Spectroscopic Instrument (DESI) a scale dependence of the order of 1020 per cent can be detected at 3σ with the null test, which will drop by a factor of 2 for a survey like the Square Kilometre Array. We also show that the null test is very insensitive to typical uncertainties in other cosmological parameters including massive neutrinos and scaledependent bias, making this a key null test for dark energy.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 February 2020
 DOI:
 10.1093/mnrasl/slz175
 arXiv:
 arXiv:1906.02217
 Bibcode:
 2020MNRAS.492L..34O
 Keywords:

 gravitation;
 dark energy;
 largescale structure of Universe;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 General Relativity and Quantum Cosmology
 EPrint:
 v1: 6 pages, 3 figures. v2: 6 pages, 4 figures, new paragraph on nonlinearities, matches version published in MNRAS Letters