Study of the Magnitude-Redshift Relation for type Ia Supernovae in a Model resulting from a Ricci-Symmetry

TL;DR

This paper explores a cosmological model derived from Ricci-symmetry that predicts a dynamic cosmological term, fitting supernova data well and suggesting a positive mbda and accelerating universe.

Contribution

It introduces a new cosmological model based on Ricci-symmetry that naturally leads to a variable mbda and fits supernova observations without ad-hoc assumptions.

Findings

Model requires mbda to be a function of the scale factor.

Best fit flat model has mbda consistent with mbda > 0.

Model predicts a negative deceleration parameter indicating acceleration.

Abstract

Models with a dynamic cosmological term \Lambda (t) are becoming popular as they solve the cosmological constant problem in a natural way. Instead of considering any ad-hoc assumption for the variation of \Lambda, we consider a particular symmetry, the contracted Ricci-collineation along the fluid flow, in Einstein's theory. We show that apart from having interesting properties, this symmetry does require \Lambda to be a function of the scale factor of the Robertson-Walker metric. In order to test the consistency of the resulting model with observations, we study the magnitude-redshift relation for the type Ia supernovae data from Perlmutter et al. The data fit the model very well and require a positive non-zero \Lambda and a negative deceleration parameter. The best-fitting flat model is obtained as \Omega_0 \approx 0.5 with q_0 \approx -0.2.