Paper: astro-ph/0512576
Date: Thu, 22 Dec 2005 19:23:09 GMT (210kb)

Title: Constraints on the Physical Parameters of the Dark Energy Using a
Model-Independent Approach

Authors: Ruth A. Daly and S. G. Djorgovski

Comments: 10 pages, 20 figures, submitted for publication
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Understanding the physical nature of the dark energy which appears to drive
the accelerated expansion of the unvierse is one of the key problems in physics
and cosmology today. This important problem is best studied using a variety of
mutually complementary approaches. Daly and Djorgovski (2003, 2004) proposed a
model independent approach to determine a number of important physical
parameters of the dark energy as functions of redshift directly from the data.
Here, we expand this method to include the determinations of its potential and
kinetic energy as functions of redshift. We show that the dark energy potential
and kinetic energy may be written as combinations of the first and second
derivatives of the coordinate distance with respect to redshift. We expand the
data set to include new supernova measurements, and now use a total of 248
coordinate distances that span the redshift range from zero to 1.79. First and
second derivatives of the coordinate distance are obtained as functions of
redshift, and these are combined to determine the potential and kinetic energy
of the dark energy as functions of redshift. An update on the redshift behavior
of the dimensionless expansion rate E(z), the acceleration rate q(z), and the
dark energy pressure p(z), energy density f(z), and equation of state w(z) is
also presented. We find that the standard Omega = 0.3 and Lambda = 0.7 model is
in an excellent agreement with the data. We also show tentative evidence that
the Cardassian and Chaplygin gas models in a spatially flat universe do not fit
the data as well.

\\ ( http://arXiv.org/abs/astro-ph/0512576 , 210kb)