Cosmography and constraints on the equation of state of the Universe in various parametrizations
Abstract
We use cosmography to present constraints on the kinematics of the Universe, without postulating any underlying theoretical model. To this end, we use a Monte Carlo Markov chain analysis to perform comparisons to the supernova Ia Union 2 compilation, combined with the Hubble Space Telescope measurements of the Hubble constant, and the Hubble parameter data sets. We introduce a sixth order cosmographic parameter and show that it does not enlarge considerably the posterior distribution when comparing to the fifth order results. We also propose a way to construct viable parameter variables to be used as alternatives of the redshift z. These can overcome both the problems of divergence and lack of accuracy associated with the use of z. Moreover, we show that it is possible to improve the numerical fits by reparametrizing the cosmological distances. In addition, we constrain the equation of state of the Universe as a whole by the use of cosmography. Thus, we derive expressions which can be directly used to fit the equation of state and the pressure derivatives up to fourth order. To this end, it is necessary to depart from a pure cosmographic analysis and to assume the Friedmann equations as valid. All our results are consistent with the ΛCDM model, although alternative fluid models, with nearly constant pressure and no cosmological constant, match the results accurately as well.
 Publication:

Physical Review D
 Pub Date:
 December 2012
 DOI:
 10.1103/PhysRevD.86.123516
 arXiv:
 arXiv:1204.2007
 Bibcode:
 2012PhRvD..86l3516A
 Keywords:

 98.80.k;
 98.80.Jk;
 98.80.Es;
 Cosmology;
 Mathematical and relativistic aspects of cosmology;
 Observational cosmology;
 Astrophysics  Cosmology and Extragalactic Astrophysics;
 General Relativity and Quantum Cosmology
 EPrint:
 23 pages. 1 reference added. Minor corrections