What is the Price of Abandoning Dark Matter? Cosmological Constraints on Alternative Gravity Theories
Abstract
Any successful alternative gravity theory that obviates the need for dark matter must fit our cosmological observations. Measurements of microwave background polarization trace the largescale baryon velocity field at recombination and show very strong O (1 ) baryon acoustic oscillations. Measurements of the largescale structure of galaxies at low redshift show much weaker features in the spectrum. If the alternative gravity theory's dynamical equations for the growth rate of structure are linear, then the density field growth can be described by a Green's function: δ (x → ,t )=δ (x → ,t^{'})G (x ,t ,t^{'}) . We show that the Green's function G (x ,t ,t^{'}) must have dramatic features that erase the initial baryon oscillations. This implies an acceleration law that changes sign on the ∼150 Mpc scale. On the other hand, if the alternative gravity theory has a large nonlinear term that couples modes on different scales, then the theory would predict largescale nonGaussian features in largescale structure. These are not seen in the distribution of galaxies nor in the distribution of quasars. No proposed alternative gravity theory for dark matter seems to satisfy these constraints.
 Publication:

Physical Review Letters
 Pub Date:
 November 2020
 DOI:
 10.1103/PhysRevLett.125.211101
 arXiv:
 arXiv:2007.00555
 Bibcode:
 2020PhRvL.125u1101P
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics;
 General Relativity and Quantum Cosmology
 EPrint:
 6 pages, 3 figures. v2: matches version accepted for publication in PRL