Low-redshift constraints on homogeneous and isotropic universes with torsion

TL;DR

This paper investigates how spacetime torsion, an extension of General Relativity, affects cosmic acceleration by analyzing low-redshift supernova and Hubble data, constraining torsion's contribution to the universe's expansion.

Contribution

It provides the first observational constraints on homogeneous and isotropic torsion models using recent low-redshift data, including a steady-state torsion assumption.

Findings

Models without a cosmological constant and with torsion are strongly disfavoured by data.

Torsion's contribution to cosmic expansion is constrained to a few percent.

Results are robust under alternative torsion parametrizations.

Abstract

One of the possible extensions of Einstein's General Theory of Relativity consists in allowing for the presence of spacetime torsion. The form of the underlying torsion tensor can be chosen such that the homogeneity and isotropy of Friedmann-Lemaitre-Robertson-Walker universes is preserved, and it has been recently suggested that such universes may undergo accelerating phases. We use recent low-redshift data, coming from Type Ia Supernova and Hubble parameter measurements, to phenomenologically constrain this class of models under the so-called steady-state torsion assumption of a constant fractional contribution of torsion to the volume expansion. We start by considering models without a cosmological constant (where torsion itself would be expected to yield the current acceleration of the universe) finding, in agreement with other recent works, that these are strongly disfavoured by the data. We then treat these models as one-parameter extensions of $\Lambda$CDM, constraining the relative contribution of torsion to the level of a few percent in appropriate units. Finally, we briefly discuss how these constraints may be improved by forthcoming low-redshift data and check the robustness of our results by studying an alternative to the steady-state torsion parametrization.