32,733 research outputs found
Majority-vote on directed Small-World networks
On directed Small-World networks the
Majority-vote model with noise is now studied through Monte Carlo
simulations. In this model, the order-disorder phase transition of the order
parameter is well defined in this system. We calculate the value of the
critical noise parameter q_c for several values of rewiring probability p of
the directed Small-World network. The critical exponentes beta/nu, gamma/nu and
1/nu were calculated for several values of p.Comment: 16 pages including 9 figures, for Int. J. Mod. Phys.
Remarks on a Decrumpling Model of the Universe
It is argued that when the dimension of space is a constant integer the full
set of Einstein's field equations has more information than the spatial
components of Einstein's equation plus the energy conservation law. Applying
the former approach to the decrumpling FRW cosmology recently proposed, it is
shown that the spacetime singularity cannot be avoided and that turning points
are absent. This result is in contrast to the decrumpling nonsingular spacetime
model with turning points previously obtained using the latter approach.Comment: 8 pages, latex, no figure
Ising model spin S=1 on directed Barabasi-Albert networks
On directed Barabasi-Albert networks with two and seven neighbours selected
by each added site, the Ising model with spin S=1/2 was seen not to show a
spontaneous magnetisation. Instead, the decay time for flipping of the
magnetisation followed an Arrhenius law for Metropolis and Glauber algorithms,
but for Wolff cluster flipping the magnetisation decayed exponentially with
time. On these networks the
Ising model spin S=1 is now studied through Monte Carlo simulations.
However, in this model, the order-disorder phase transition is well defined
in this system. We have obtained a first-order phase transition for values of
connectivity m=2 and m=7 of the directed Barabasi-Albert network.Comment: 8 pages for Int. J. Mod. Phys. C; e-mail: [email protected]
Simulation of majority rule disturbed by power-law noise on directed and undirected Barabasi-Albert networks
On directed and undirected Barabasi-Albert networks the Ising model with spin
S=1/2 in the presence of a kind of noise is now studied through Monte Carlo
simulations. The noise spectrum P(n) follows a power law, where P(n) is the
probability of flipping randomly select n spins at each time step. The noise
spectrum P(n) is introduced to mimic the self-organized criticality as a model
influence of a complex environment. In this model, different from the square
lattice, the order-disorder phase transition of the order parameter is not
observed. For directed Barabasi-Albert networks the magnetisation tends to zero
exponentially and for undirected Barabasi-Albert networks, it remains constant.Comment: 6 pages including many figures, for Int. J. Mod. Phys.
Dynamics and Constraints of the Massive Gravitons Dark Matter Flat Cosmologies
We discuss the dynamics of the universe within the framework of Massive
Graviton Dark Matter scenario (MGCDM) in which gravitons are geometrically
treated as massive particles. In this modified gravity theory, the main effect
of the gravitons is to alter the density evolution of the cold dark matter
component in such a way that the Universe evolves to an accelerating expanding
regime, as presently observed. Tight constraints on the main cosmological
parameters of the MGCDM model are derived by performing a joint likelihood
analysis involving the recent supernovae type Ia data, the Cosmic Microwave
Background (CMB) shift parameter and the Baryonic Acoustic Oscillations (BAOs)
as traced by the Sloan Digital Sky Survey (SDSS) red luminous galaxies. The
linear evolution of small density fluctuations is also analysed in detail. It
is found that the growth factor of the MGCDM model is slightly different
() from the one provided by the conventional flat CDM
cosmology. The growth rate of clustering predicted by MGCDM and CDM
models are confronted to the observations and the corresponding best fit values
of the growth index () are also determined. By using the expectations
of realistic future X-ray and Sunyaev-Zeldovich cluster surveys we derive the
dark-matter halo mass function and the corresponding redshift distribution of
cluster-size halos for the MGCDM model. Finally, we also show that the Hubble
flow differences between the MGCDM and the CDM models provide a halo
redshift distribution departing significantly from the ones predicted by other
DE models. These results suggest that the MGCDM model can observationally be
distinguished from CDM and also from a large number of dark energy
models recently proposed in the literature.Comment: Accepted for publication in Physical Review D (12 pages, 4 figures
Thermodynamics of Decaying Vacuum Cosmologies
The thermodynamic behavior of vacuum decaying cosmologies is investigated
within a manifestly covariant formulation. Such a process corresponds to a
continuous irreversible energy flow from the vacuum component to the created
matter constituents. It is shown that if the specific entropy per particle
remains constant during the process, the equilibrium relations are preserved.
In particular, if the vacuum decays into photons, the energy density and
average number density of photons scale with the temperature as and . The temperature law is determined and a generalized
Planckian type form of the spectrum, which is preserved in the course of the
evolution, is also proposed. Some consequences of these results for decaying
vacuum FRW type cosmologies as well as for models with ``adiabatic'' photon
creation are discussed.Comment: 21 pages, uses LATE
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