Constraining alternatives to a cosmological constant: Generalized couplings and scale invariance

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