Year: 2018
Type: article
Abstract: The standard cosmographic approach consists in performing a series expansion of a cosmological observable around z =0 and then using the data to constrain the cosmographic (or kinematic) parameters at present time. Such a procedure works well if applied to redshift ranges inside the z -series convergence radius ( z <1), but can be problematic if we want to cover redshift intervals that fall outside the z −series convergence radius. This problem can be circumvented if we work with the y −redshift, y = z /(1+ z ), or the scale factor, a =1/(1+ z )=1− y , for example. In this paper, we use the scale factor a as the variable of expansion. We expand the luminosity distance and the Hubble parameter around an arbitrary ã and use the Supernovae Ia (SNe Ia) and the Hubble parameter data to estimate H , q , j and s at z ≠0 ( ã ≠1). We show that the last relevant term for both expansions is the third. Since the third order expansion of d L ( z ) has one parameter less than the third order expansion of H ( z ), we also consider, for completeness, a fourth order expansion of d L ( z ). For the third order expansions, the results obtained from both SNe Ia and H ( z ) data are incompatible with the ΛCDM model at 2σ confidence level, but also incompatible with each other. When the fourth order expansion of d L ( z ) is taken into account, the results obtained from SNe Ia data are compatible with the ΛCDM model at 2σ confidence level, but still remains incompatible with results obtained from H ( z ) data. These conflicting results may indicate a tension between the current SNe Ia and H ( z ) data sets.
Authors: C. Rodrigues Filho, Edésio M. Barboza Jr.
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2610777359