10 research outputs found
Search for Tracker Potentials in Quintessence Theory
We report a significant finding in Quintessence theory that the the scalar
fields with tracker potentials have a model-independent scaling behaviour in
the expanding universe. So far widely discussed exponential,power law or
hyperbolic potentials can simply mimic the tracking behaviour over a limited
range of redshift. In the small redshift range where the variation of the
tracking parameter may be taken to be negligible, the differential
equation of generic potentials leads to hyperbolic sine and hyperbolic cosine
potentials which may approximate tracker field in the present day universe. We
have plotted the variation of tracker potential and the equation of state of
the tracker field as function of the redshift for the model-independent
relation derived from tracker field theory; we have also plotted the variation
of in terms of the scalar field for the chosen hyperbolic
cosine function and have compared with the curves obtained by reconstruction of
from the real observational data from the supernovae.Comment: 11 pages, 3 figures, late
Phenomemology of a Realistic Accelerating Universe Using Tracker Fields
We present a realistic scenario of tracking of scalar fields with varying
equation of state. The astrophysical constraints on the evolution of scalar
fields in the physical universe are discussed. The nucleosynthesis and the
galaxy formation constraints have been used to put limits on and
estimate during cosmic evolution. Interpolation techniques have been
applied to estimate at the present epoch. The epoch of
transition from matter to quintessence dominated era and consequent onset of
acceleration in cosmic expansion is calculated and taking the lower limit
as estimated from data, it is shown that the
supernova observations beyond redshift would reveal deceleration in
cosmic expansion.Comment: 10 pages, 4 figures, late
Parametrization of dark energy equation of state Revisited
A comparative study of various parametrizations of the dark energy equation
of state is made. Astrophysical constraints from LSS, CMB and BBN are laid down
to test the physical viability and cosmological compatibility of these
parametrizations. A critical evaluation of the 4-index parametrizations reveals
that Hannestad-M\"{o}rtsell as well as Lee parametrizations are simple and
transparent in probing the evolution of the dark energy during the expansion
history of the universe and they satisfy the LSS, CMB and BBN constraints on
the dark energy density parameter for the best fit values.Comment: 11 page
The Genesis of Cosmological Tracker Fields
The role of the quintessence field as a probable candidate for the repulsive
dark energy, the conditions for tracking and the requisites for tracker fields
are examined. The concept of `integrated tracking' is introduced and a new
criterion for the existence of tracker potentials is derived assuming monotonic
increase in the scalar energy density parameter \Omega_\phi with the evolution
of the universe as suggested by the astrophysical constraints. It provides a
technique to investigate generic potentials of the tracker fields. The general
properties of the tracker fields are discussed and their behaviour with respect
to tracking parameter \epsilon is analyzed. It is shown that the tracker fields
around the limiting value \epsilon \simeq \frac 23 give the best fit with the
observational constraints.Comment: 8 pages, Latex file, 1 figure, comments adde
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