Testing and selection of cosmological models with $(1+z{)}^6$ corrections

In the paper we check whether the contribution of $(-)(1+z{)}^6$ type in the Friedmann equation can be tested. We consider some astronomical tests to constrain the density parameters in such models. We describe different interpretations of such an additional term: geometric effects of loop quantum cosmology, effects of braneworld cosmological models, nonstandard cosmological models in metric-affine gravity, and models with spinning fluid. Kinematical (or geometrical) tests based on null geodesics are insufficient to separate individual matter components when they behave like perfect fluid and scale in the same way. Still, it is possible to measure their overall effect. We use recent measurements of the coordinate distances from the Fanaroff-Riley type IIb radio galaxy data, supernovae type Ia data, baryon oscillation peak and cosmic microwave background radiation observations to obtain stronger bounds for the contribution of the type considered. We demonstrate that, while ${\rho }^2$ corrections are very small, they can be tested by astronomical observations—at least in principle. Bayesian criteria of model selection (the Bayesian factor, AIC, and BIC) are used to check if additional parameters are detectable in the present epoch. As it turns out, the $\Lambda \mathrm{CDM}$ model is favored over the bouncing model driven by loop quantum effects. Or, in other words, the bounds obtained from cosmography are very weak, and from the point of view of the present data this model is indistinguishable from the $\Lambda \mathrm{CDM}$ one.

Figure 1

The 68.3% and 95.4% confidence levels (obtained from combined analysis of $\mathrm{SN}+\mathrm{RG}+\mathrm{SDSS}+\mathrm{CMBR}$) on the $({\Omega }_{\mathrm{m},0},{\Omega }_{\Lambda ,0})$ plane.