Testing non-standard cosmological models with supernovae

TL;DR

This paper tests a non-standard cosmological model involving a new density parameter using supernova data, constraining the contribution of non-Riemannian spacetime structures to the universe's late-time acceleration.

Contribution

It introduces and constrains a novel non-Riemannian density parameter in cosmology, extending the standard model with a correction term inspired by metric-affine gravity.

Findings

Limits on the contribution of the new density parameter at low redshifts.

The model's numerical results are applicable to certain anisotropic cosmologies.

Redshift binning affects the parameter constraints.

Abstract

In this work we study the magnitude-redshift relation of a non-standard cosmological model. The model under consideration was firstly investigated within a special case of metric-affine gravity (MAG) and was recently recovered via different approaches by two other groups. Apart from the usual cosmological parameters for pressure-less matter $\Omega_{\rm m}$, cosmological constant/dark energy $\Omega_{\lambda}$, and radiation $\Omega_{\rm r}$ a new density parameter $\Omega_\psi$ emerges. The field equations of the model reduce to a system which is effectively given by the usual Friedmann equations of general relativity, supplied by a correction to the energy density and pressure in form of $\Omega_\psi$, which is related to the non-Riemannian structure of the underlying spacetime. We search for the best-fit parameters by using recent SN Ia data sets and constrain the possible contribution of a new dark-energy like component at low redshifts, thereby we put an upper limit on the presence of non-Riemannian quantities in the late stages of the universe. In addition the impact of placing the data in redshift bins of variable size is studied. The numerical results of this work also apply to several anisotropic cosmological models which, on the level of the field equations, exhibit a similar scaling behavior of the density parameters like our non-Riemannian model.