Cosmological constraints from supernova data set with corrected redshift
  Observations of distant type Ia supernovae (SNe Ia), used as standard
candles, support the notion that the Cosmos is filled with a mysterious form of
energy, the dark energy. The constraints on cosmological parameters derived
from data of SNe Ia and the measurements of the cosmic microwave background
anisotropies indicate that the dark energy amounts to roughly 70% of all the
energy contained in the Universe. In the hypothesis of a flat Universe, we
investigate if the dark energy is really required in order to explain the SNe
Ia experimental data, and, in this case, how much of such unknown energy is
actually deduced from the analysis of these data and must be introduced in the
LambdaCDM model of cosmology. In particular we are interested in verifying if
the Einstein-de Sitter model of the expanding Universe is really to be ruled
out. By using a fitting procedure based on the Newton method search for a
minimum, we reanalyzed the "Union compilation" reported by Kowalski et al.
(2008) formed by 307 SNe, obtaining a very different estimate of the dark
energy, that is roughly 60%. Furthermore, in order to balance the correction of
the apparent magnitude of SNe Ia, due to the dilation or stretching of the
corresponding light curve width, we introduce a suitable modified redsfhit.
Taking into account this correction, we refitted the Union compilation dataset
after a selection cut. The main result that emerges from our analysis is that
the values of Omega_m and Omega_Lambda strongly depend on the fitting procedure
and the selected sample. In particular, the constraint we obtain on the mass
density, normalized by the critical mass density, is Omega_m = 0.7 for a sample
of 252, and Omega_m = 1 for a sample of 242 SNe Ia respectively. The latter
case does not imply the existence of any additional form of dark energy.
