High redshift cosmography: new results and implication for dark energy
  The explanation of the accelerated expansion of the Universe poses one of the
most fundamental questions in physics and cosmology today. If the acceleration
is driven by some form of dark energy, one can try to constrain the parameters
using a cosmographic approach. Our high-redshift analysis allows us to put
constraints on the cosmographic expansion up to the fifth order. It is based on
the Union2 Type Ia Supernovae (SNIa) data set, the Hubble diagram constructed
from some Gamma Ray Bursts luminosity distance indicators, and gaussian priors
on the distance from the Baryon Acoustic Oscillations (BAO), and the Hubble
constant h (these priors have been included in order to help break the
degeneracies among model parameters). To perform our statistical analysis and
to explore the probability distributions of the cosmographic parameters we use
the Markov Chain Monte Carlo Method (MCMC). We finally investigate implications
of our results for the dark energy, in particular, we focus on the
parametrization of the dark energy equation of state (EOS). Actually, a
possibility to investigate the nature of dark energy lies in measuring the dark
energy equation of state, w, and its time (or redshift) dependence at high
accuracy. However, since w(z) is not directly accessible to measurement,
reconstruction methods are needed to extract it reliably from observations.
Here we investigate different models of dark energy, described through several
parametrizations of the equation of state, by comparing the cosmographic and
the EOS series.
