29,603 research outputs found
On the equivalence of Lambda(t) and gravitationally induced particle production cosmologies
The correspondence between cosmological models powered by a decaying vacuum
energy density and gravitationally induced particle production is investigated.
Although being physically different in the physics behind them we show that
both classes of cosmologies under certain conditions can exhibit the same
dynamic and thermodynamic behavior. Our method is applied to obtain three
specific models that may be described either as Lambda(t)CDM or gravitationally
induced particle creation cosmologies. In the point of view of particle
production models, the later class of cosmologies can be interpreted as a kind
of one-component unification of the dark sector. By using current type Ia
supernovae data, recent estimates of the cosmic microwave background shift
parameter and baryon acoustic oscillations measurements we also perform a
statistical analysis to test the observational viability within the two
equivalent classes of models and we obtain the best-fit of the free parameters.
By adopting the Akaike information criterion we also determine the rank of the
models considered here. Finally, the particle production cosmologies (and the
associated decaying Lambda(t)-models) are modeled in the framework of field
theory by a phenomenological scalar field model.Comment: 9 pages, 3 figures, new comments and 8 references added. Accepted for
publication in Physics Letters
Accessing the Acceleration of the Universe with Sunyaev-Zel'dovich and X-ray Data from Galaxy Clusters
By using exclusively the Sunyaev-Zel'dovich effect and X-ray surface
brightness data from 25 galaxy clusters in the redshift range 0.023< z < 0.784
we access cosmic acceleration employing a kinematic description. Such result is
fully independent on the validity of any metric gravity theory, the possible
matter-energy contents filling the Universe, as well as on the SNe Ia Hubble
diagram.Comment: 3 pages, 4 figures, To appear in the Proceedings of the Twelfth
Marcel Grossmann Meeting on General Relativit
Are Galaxy Clusters Suggesting an Accelerating Universe?
The present cosmic accelerating stage is discussed through a new kinematic
method based on the Sunyaev- Zel'dovich effect (SZE) and X-ray surface
brightness data from galaxy clusters. By using the SZE/X-ray data from 38
galaxy clusters in the redshift range [Bonamente et
al., Astrop. J. {\bf 647}, 25 (2006)] it is found that the present Universe is
accelerating and that the transition from an earlier decelerating to a late
time accelerating regime is relatively recent. The ability of the ongoing
Planck satellite mission to obtain tighter constraints on the expansion history
through SZE/X-ray angular diameters is also discussed. Our results are fully
independent on the validity of any metric gravity theory, the possible matter-
energy contents filling the Universe, as well as on the SNe Ia Hubble diagram
from which the presenting accelerating stage was inferred.Comment: 6 pages, 6 figures, AIP Conf. Proc. Invisible Universe: Proceedings
of the Conferenc
Formation of Dark Matter Haloes in a Homogeneous Dark Energy Universe
Several independent cosmological tests have shown evidences that the energy
density of the Universe is dominated by a dark energy component, which cause
the present accelerated expansion. The large scale structure formation can be
used to probe dark energy models, and the mass function of dark matter haloes
is one of the best statistical tools to perform this study. We present here a
statistical analysis of mass functions of galaxies under a homogeneous dark
energy model, proposed in the work of Percival (2005), using an observational
flux-limited X-ray cluster survey, and CMB data from WMAP. We compare, in our
analysis, the standard Press-Schechter (PS) approach (where a Gaussian
distribution is used to describe the primordial density fluctuation field of
the mass function), and the PL (Power Law) mass function (where we apply a
nonextensive q-statistical distribution to the primordial density field). We
conclude that the PS mass function cannot explain at the same time the X-ray
and the CMB data (even at 99% confidence level), and the PS best fit dark
energy equation of state parameter is , which is distant from the
cosmological constant case. The PL mass function provides better fits to the
HIFLUGCS X-ray galaxy data and the CMB data; we also note that the
parameter is very sensible to modifications in the PL free parameter, ,
suggesting that the PL mass function could be a powerful tool to constrain dark
energy models.Comment: 4 pages, 2 figures, Latex. Accepted for publication in the
International Journal of Modern Physics D (IJMPD)
Experience with the Open Source based implementation for ATLAS Conditions Data Management System
Conditions Data in high energy physics experiments is frequently seen as
every data needed for reconstruction besides the event data itself. This
includes all sorts of slowly evolving data like detector alignment, calibration
and robustness, and data from detector control system. Also, every Conditions
Data Object is associated with a time interval of validity and a version.
Besides that, quite often is useful to tag collections of Conditions Data
Objects altogether. These issues have already been investigated and a data
model has been proposed and used for different implementations based in
commercial DBMSs, both at CERN and for the BaBar experiment. The special case
of the ATLAS complex trigger that requires online access to calibration and
alignment data poses new challenges that have to be met using a flexible and
customizable solution more in the line of Open Source components. Motivated by
the ATLAS challenges we have developed an alternative implementation, based in
an Open Source RDBMS. Several issues were investigated land will be described
in this paper:
-The best way to map the conditions data model into the relational database
concept considering what are foreseen as the most frequent queries.
-The clustering model best suited to address the scalability problem.
-Extensive tests were performed and will be described.
The very promising results from these tests are attracting the attention from
the HEP community and driving further developments.Comment: 8 pages, 4 figures, 3 tables, conferenc
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