We present a comparative analysis of observational low-redshift background constraints on three candidate models for explaining the low-redshift 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 low-redshift 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 time-dependent cosmological constant. In this case we show that a matter density ${\Omega }_m\sim 0.3$ is a relatively poor fit to the data, and the best-fit model would require a fluid with a much smaller density and a significantly positive equation of state parameter.

我们介绍了三种候选模型的观测低红移背景约束条件的比较分析，用于解释宇宙的低红移加速度。Feng和Carloni的广义耦合模型以及Maeder的尺度不变模型（都可以解释为双度量理论）与Chevallier，Polarski和Linder的传统参数化进行了比较。原则上，广义耦合模型在真空中等效于广义相对论，它包含两种类型的真空能：通常的宇宙学常数加上物质场的第二贡献。我们表明，前者是模型与低红移观测值保持一致所必需的，而没有统计上显着的证据表明存在第二个。另一方面，尺度不变模型实际上具有随时间变化的宇宙常数。在这种情况下，我们表明物质密度${\Omega }_{米}〜0。3$ 对数据的拟合相对较差，最佳拟合模型将需要密度小得多且状态参数方程明显为正的流体。