Constraining alternatives to a cosmological constant: Generalized couplings and scale invariance
Abstract
We present a comparative analysis of observational lowredshift background constraints on three candidate models for explaining the lowredshift acceleration of the universe. The generalized coupling model by Feng and Carloni and the scale invariant model by Maeder (both of which can be interpreted as bimetric theories) are compared to the traditional parametrization of Chevallier, Polarski and Linder. In principle the generalized coupling model, which in vacuum is equivalent to General Relativity, contains two types of vacuum energy: the usual cosmological constant plus a second contribution due to the matter fields. We show that the former is necessary for the model to agree with lowredshift observations, while there is no statistically significant evidence for the presence of the second. On the other hand the scale invariant model effectively has a timedependent cosmological constant. In this case we show that a matter density Ω_{m} ∼ 0 . 3 is a relatively poor fit to the data, and the bestfit model would require a fluid with a much smaller density and a significantly positive equation of state parameter.
 Publication:

Physics of the Dark Universe
 Pub Date:
 January 2021
 DOI:
 10.1016/j.dark.2020.100761
 arXiv:
 arXiv:2012.10513
 Bibcode:
 2021PDU....3100761F
 Keywords:

 Cosmology;
 Dark energy;
 Modified gravity;
 Cosmological observations;
 Statistical analysis;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 General Relativity and Quantum Cosmology;
 High Energy Physics  Phenomenology
 EPrint:
 15 pages, 6 figures, Physics of the Dark Universe (in press)