21,209 research outputs found
Constraints on a new alternative model to dark energy
The recent type Ia supernova data suggest that the universe is accelerating
now and decelerated in recent past. This may provide the evidence that the
standard Friedmann equation needs to be modified. We analyze in detail a new
model in the context of modified Friedmann equation using the supernova data
published by the High- Supernova Search Team and the Supernova Cosmology
Project. The new model explains recent acceleration and past deceleration.
Furthermore, the new model also gives a decelerated universe in the future.Comment: 12 pages, 5 figures, use ws-ijmpd, minor changes made. In the new
version, a detailed derivation of the model is give
Chaplygin Gravitodynamics
We consider a new approach for gravity theory coupled to Chaplygin matter in
which the {\it{relativistic}} formulation of the latter is of crucial
importance. We obtain a novel form of matter with dust like density and negative pressure. We explicitly show that our results are
compatible with a relativistic generalization of the energy conservation
principle, derived here.Comment: Title changed, Revised version,N o change in conclusions, Journal
ref.: MPL A21 (2006)1511-151
Cosmological Dynamics of a Dirac-Born-Infeld field
We analyze the dynamics of a Dirac-Born-Infeld (DBI) field in a cosmological
set-up which includes a perfect fluid. Introducing convenient dynamical
variables, we show the evolution equations form an autonomous system when the
potential and the brane tension of the DBI field are arbitrary power-law or
exponential functions of the DBI field. In particular we find scaling solutions
can exist when powers of the field in the potential and warp-factor satisfy
specific relations. A new class of fixed-point solutions are obtained
corresponding to points which initially appear singular in the evolution
equations, but on closer inspection are actually well defined. In all cases, we
perform a phase-space analysis and obtain the late-time attractor structure of
the system. Of particular note when considering cosmological perturbations in
DBI inflation is a fixed-point solution where the Lorentz factor is a finite
large constant and the equation of state parameter of the DBI field is .
Since in this case the speed of sound becomes constant, the solution can
be thought to serve as a good background to perturb about.Comment: 24 pages, 7 figures, minor corrections, references adde
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