6,745 research outputs found
Toward reconstruction of dynamics of the Universe from distant supernovae type Ia
We demonstrate a model-independent method of estimating qualitative dynamics
of an accelerating universe from observations of distant type Ia supernovae.
Our method is based on the luminosity-distance function, optimized to fit
observed distances of supernovae, and the Hamiltonian representation of
dynamics for the quintessential universe with a general form of equation of
state . Because of the Hamiltonian structure of FRW dynamics
with the equation of state , the dynamics is uniquelly
determined by the potential function of the system. The effectiveness of
this method in discrimination of model parameters of Cardassian evolution
scenario is also given. Our main result is the following, restricting to the
flat model with the current value of , the constraints at
confidence level to the presence of modification of the
FRW models are .Comment: 15 pages, 12 figures, RevTeX
Phantom cosmology as a simple model with dynamical complexity
We study the Friedmann-Robertson-Walker model with phantom fields modelled in
terms of scalar fields. We apply the Ziglin theory of integrability and find
that the flat model is nonintegrable. Then we cannot expect to determine simple
analytical solutions of the Einstein equations. We demonstrate that there is
only a discrete set of parameters where this model is integrable. For
comparison we describe the phantoms fields in terms of the barotropic equation
of state. It is shown that in the contrast to the phantoms modelled as scalar
fields, the dynamics is always integrable and phase portraits are constructed.
In this case we find the duality relation.Comment: RevTeX4, 11 pages, 2 figures; rewritten (v.2); new section on complex
dynamics in cases with and without spontaneous symmetry breaking (v.3); this
new section on numerical analysis of complex dynamics was dropped, upload to
match version in PRE (v.4
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