28,242 research outputs found
Critical behavior of the spin-3/2 Blume-Capel model on a random two-dimensional lattice
We investigate the critical properties of the spin-3/2 Blume-Capel model in
two dimensions on a random lattice with quenched connectivity disorder. The
disordered system is simulated by applying the cluster hybrid Monte Carlo
update algorithm and re-weighting techniques. We calculate the critical
temperature as well as the critical point exponents , ,
, and . We find that, contrary of what happens to the spin-1/2
case, this random system does not belong to the same universality class as the
regular two-dimensional ferromagnetic model.Comment: 5 pages and 5 figure
Newtonian Perturbations on Models with Matter Creation
Creation of Cold Dark Matter (CCDM) can macroscopically be described by a
negative pressure, and, therefore, the mechanism is capable to accelerate the
Universe, without the need of an additional dark energy component. In this
framework we discuss the evolution of perturbations by considering a
Neo-Newtonian approach where, unlike in the standard Newtonian cosmology, the
fluid pressure is taken into account even in the homogeneous and isotropic
background equations (Lima, Zanchin and Brandenberger, MNRAS {\bf 291}, L1,
1997). The evolution of the density contrast is calculated in the linear
approximation and compared to the one predicted by the CDM model. The
difference between the CCDM and CDM predictions at the perturbative
level is quantified by using three different statistical methods, namely: a
simple -analysis in the relevant space parameter, a Bayesian
statistical inference, and, finally, a Kolmogorov-Smirnov test. We find that
under certain circumstances the CCDM scenario analysed here predicts an overall
dynamics (including Hubble flow and matter fluctuation field) which fully
recovers that of the traditional cosmic concordance model. Our basic conclusion
is that such a reduction of the dark sector provides a viable alternative
description to the accelerating CDM cosmology.Comment: Physical Review D in press, 10 pages, 4 figure
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