paper

Cosmographic evaluation of deceleration parameter using SNe Ia data

arXiv:astro-ph/0406444 · doi:10.1086/423365

Abstract

The apparent magnitude-redshift data of SNe Ia call for modifications in the standard model energy densities. Under the circumstance that this modification cannot be limited to the addition of a mere cosmological constant, a serious situation has emerged in cosmology, in which the energy densities in the universe have become largely speculative. In this situation, an equation of state of the form p=w ρitself is not well-motivated. In this paper, we argue that the reasonable option left is to make a model-independent analysis of SNe data, without reference to the energy densities. In this basically kinematic approach, we limit ourselves to the observationally justifiable assumptions of homogeneity and isotropy; i.e., to the assumption that the universe has a RW metric. This cosmographic approach is historically the original one to cosmology. We perform the analysis by expanding the scale factor into a polynomial of order 5, which assumption can be further generalised to any order. The present expansion rates h, q_0, r_0 etc. are evaluated by computing the marginal likelihoods for these parameters. These values are relevant, since any cosmological solution would ultimately need to explain them.

Accepted for publication in The Astrophysical Journal. First results presented in the conference `Provocative Universe' IUCAA, Pune, India, June 2003

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