8 research outputs found
A mathematical analysis of the evolution of perturbations in a modified Chaplygin gas model
One approach in modern cosmology consists in supposing that dark matter and
dark energy are different manifestations of a single `quartessential' fluid.
Following such idea, this work presents a study of the evolution of
perturbations of density in a flat cosmological model with a modified Chaplygin
gas acting as a single component. Our goal is to obtain properties of the model
which can be used to distinguish it from another cosmological models which have
the same solutions for the general evolution of the scale factor of the
universe, without the construction of the power spectrum. Our analytical
results, which alone can be used to uniquely characterize the specific model
studied in our work, show that the evolution of the density contrast can be
seen, at least in one particular case, as composed by a spheroidal wave
function. We also present a numerical analysis which clearly indicates as one
interesting feature of the model the appearence of peaks in the evolution of
the density constrast.Comment: 21 pages, accepted for publication in General Relativity and
Gravitatio
Observational Constraints on Chaplygin Quartessence: Background Results
We derive the constraints set by several experiments on the quartessence
Chaplygin model (QCM). In this scenario, a single fluid component drives the
Universe from a nonrelativistic matter-dominated phase to an accelerated
expansion phase behaving, first, like dark matter and in a more recent epoch
like dark energy. We consider current data from SNIa experiments, statistics of
gravitational lensing, FR IIb radio galaxies, and x-ray gas mass fraction in
galaxy clusters. We investigate the constraints from this data set on flat
Chaplygin quartessence cosmologies. The observables considered here are
dependent essentially on the background geometry, and not on the specific form
of the QCM fluctuations. We obtain the confidence region on the two parameters
of the model from a combined analysis of all the above tests. We find that the
best-fit occurs close to the CDM limit (). The standard
Chaplygin quartessence () is also allowed by the data, but only at
the level.Comment: Replaced to match the published version, references update
Dynamics of Modified Chaplygin Gas in Brane World Scenario: Phase Plane Analysis
In this work we investigate the background dynamics when dark energy is
coupled to dark matter with a suitable interaction in the universe described by
brane cosmology. Here DGP and the RSII brane models have been considered
separately. Dark energy in the form of modified Chaplygin gas is considered. A
suitable interaction between dark energy and dark matter is considered in order
to at least alleviate (if not solve) the cosmic coincidence problem. The
dynamical system of equations is solved numerically and a stable scaling
solution is obtained. A significant attempt towards the solution of the cosmic
coincidence problem is taken. The statefinder parameters are also calculated to
classify the dark energy models. Graphs and phase diagrams are drawn to study
the variations of these parameters. It is also seen that the background
dynamics of modified Chaplygin gas is completely consistent with the notion of
an accelerated expansion in the late universe. Finally, it has been shown that
the universe in both the models follows the power law form of expansion around
the critical point, which is consistent with the known results.Comment: 14 pages, 14 figure
Dynamics of Interacting Generalized Cosmic Chaplygin gas in Brane-world scenario
In this work we explore the background dynamics when dark energy is coupled
to dark matter with a suitable interaction in the universe described by brane
cosmology. Here DGP and the RSII brane models have been considered separately.
Dark energy in the form of Generalized Cosmic Chaplygin gas is considered. A
suitable interaction between dark energy and dark matter is considered in order
to at least alleviate (if not solve) the cosmic coincidence problem. The
dynamical system of equations is solved numerically and a stable scaling
solution is obtained. A significant attempt towards the solution of the cosmic
coincidence problem is taken. The statefinder parameters are also calculated to
classify the dark energy models. Graphs and phase diagrams are drawn to study
the variations of these parameters. It is also seen that the background
dynamics of Generalized Cosmic Chaplygin gas is consistent with the late cosmic
acceleration, but not without satisfying certain conditions. It has been shown
that the universe in both the models follows the power law form of expansion
around the critical point, which is consistent with the known results. Future
singularities were studied and our models were declared totally free from any
types of such singularities. Finally, some cosmographic parameters were also
briefly studied. Our investigation led to the fact that although GCCG with a
far lesser negative pressure compared to other DE models, can overcome the
relatively weaker gravity of RS II brane, with the help of the negative brane
tension, yet for the DGP brane model with much higher gravitation, the
incompetency of GCCG is exposed, and it cannot produce the accelerating
scenario until it reaches the phantom era.Comment: 34 pages, 30 figures. arXiv admin note: substantial text overlap with
arXiv:1204.3531, arXiv:1109.1481, arXiv:1109.357
The SPES production target
An extended work is in progress concerning the target development for the SPES (Selective Production of Exotic Species) project. The SPES will be an ISOL based facility (Isotope Separation On Line) in which a proton beam of 40 MeV and 0.2 mA impinges directly on a uranium carbide target. After the mass separation and re-acceleration on the experimental sites, the RIBs will have an intensity of the order of 10^9 pps (for 132Sn) and an energy up to 13 MeV/u. The new idea that characterize this project is the design of its target: we propose a target configuration capable to keep high the number of fissions, low the power deposition and fast the release of the produced isotopes
Production of high-intensity RIB at SPES
The SPES Project at INFN Laboratori Nazionali di Legnaro [1] is now in its early construction phase. SPES is an ISOL type Radioactive Ion Beam (RIB) [2] facility for the production of neutron-rich radioactive nuclei by uranium fission. RIBs will be produced by proton induced fission on a UCx multi foil direct target at a rate of 10^13 fps, more than one order of magnitude larger than the currently available beam intensities. The recent developments on the production, ionization and acceleration of RIBs at SPES are hereafter presented