353 research outputs found
Quantization of Soliton Cellular Automata
A method of quantization of classical soliton cellular automata (QSCA) is put
forward that provides a description of their time evolution operator by means
of quantum circuits that involve quantum gates from which the associated
Hamiltonian describing a quantum chain model is constructed.
The intrinsic parallelism of QSCA, a phenomenon first known from quantum
computers, is also emphasized.Comment: Latex, 6 pages, 1 figure in eps format included. Submitted to Journal
of Nonlinear Mathematical Physics. Special Issue of Proccedings of NEEDS'9
Exact charged black-hole solutions in D-dimensional f(T) gravity: torsion vs curvature analysis
We extract exact charged black-hole solutions with flat transverse sections
in the framework of D-dimensional Maxwell-f(T) gravity, and we analyze the
singularities and horizons based on both torsion and curvature invariants.
Interestingly enough, we find that in some particular solution subclasses there
appear more singularities in the curvature scalars than in the torsion ones.
This difference disappears in the uncharged case, or in the case where f(T)
gravity becomes the usual linear-in-T teleparallel gravity, that is General
Relativity. Curvature and torsion invariants behave very differently when
matter fields are present, and thus f(R) gravity and f(T) gravity exhibit
different features and cannot be directly re-casted each other.Comment: 24 pages, 3 figures. arXiv admin note: text overlap with
arXiv:1110.402
Rip/singularity free cosmology models with bulk viscosity
In this paper we present two concrete models of non-perfect fluid with bulk
viscosity to interpret the observed cosmic accelerating expansion phenomena,
avoiding the introduction of exotic dark energy. The first model we inspect has
a viscosity of the form by
taking into account of the decelerating parameter q, and the other model is of
the form . We give out the
exact solutions of such models and further constrain them with the latest
Union2 data as well as the currently observed Hubble-parameter dataset (OHD),
then we discuss the fate of universe evolution in these models, which confronts
neither future singularity nor little/pseudo rip. From the resulting curves by
best fittings we find a much more flexible evolution processing due to the
presence of viscosity while being consistent with the observational data in the
region of data fitting. With the bulk viscosity considered, a more realistic
universe scenario is characterized comparable with the {\Lambda}CDM model but
without introducing the mysterious dark energy.Comment: 9 pages, 6 figures, submitted to EPJ-
Quintom model with O() symmetry
We investigate the quintom model of dark energy in the generalized case where
the corresponding canonical and phantom fields possess O() symmetries.
Assuming exponential potentials we find that this O quintom paradigm
exhibits novel properties comparing to the simple canonical and phantom
scenarios. In particular, we find that the universe cannot result in a
quintessence-type solution with , even in the cases where the phantom
field seems to be irrelevant. On the contrary, there are always late-time
attractors which correspond to accelerating universes with and with a
recent crossing of the phantom divide, and for a very large area of the
parameter space they are the only ones. This is in contrast with the previous
simple-quintom results, where an accelerating universe is a possible late-time
stable solution but it is not guaranteed.Comment: 13 pages, no figur
Preventing eternality in phantom inflation
We have investigated the necessary conditions that prevent phantom inflation
from being eternal. Allowing additionally for a nonminimal coupling between the
phantom field and gravity, we present the slow-climb requirements, perform an
analysis of the fluctuations, and finally we extract the overall conditions
that are necessary in order to prevent eternality. Furthermore, we verify our
results by solving explicitly the cosmological equations in a simple example of
an exponential potential, formulating the classical motion plus the stochastic
effect of the fluctuations through Langevin equations. Our analysis shows that
phantom inflation can be finite without the need of additional exotic
mechanisms.Comment: 8 pages, V2 references added. V3 version published in Phys. Rev.
Braneworld models with a non-minimally coupled phantom bulk field: a simple way to obtain the -1-crossing at late times
We investigate general braneworld models, with a non-minimally coupled
phantom bulk field and arbitrary brane and bulk matter contents. We show that
the effective dark energy of the brane-universe acquires a dynamical nature, as
a result of the non-minimal coupling which provides a mechanism for an indirect
"bulk-brane interaction" through gravity. For late-time cosmological evolution
and without resorting to special ansatzes or to specific areas of the parameter
space, we show that the -1-crossing of its equation-of-state parameter is
general and can be easily achieved. As an example we provide a simple, but
sufficiently general, approximate analytical solution, that presents the
crossing behavior.Comment: 11 pages, 2 figure
Validity of the Generalized Second Law of Thermodynamics of the Universe Bounded by the Event Horizon in Holographic Dark Energy Model
In this letter, we investigate the validity of the generalized second law of
thermodynamics of the universe bounded by the event horizon in the holographic
dark energy model. The universe is chosen to be homogeneous and isotropic and
the validity of the first law has been assumed here. The matter in the universe
is taken in the form of non-interacting two fluid system- one component is the
holographic dark energy model and the other component is in the form of dust.Comment: 8 page
Interacting Three Fluid System and Thermodynamics of the Universe Bounded by the Event Horizon
The work deals with the thermodynamics of the universe bounded by the event
horizon. The matter in the universe has three constituents namely dark energy,
dark matter and radiation in nature and interaction between then is assumed.
The variation of entropy of the surface of the horizon is obtained from unified
first law while matter entropy variation is calculated from the Gibbss' law.
Finally, validity of the generalized second law of thermodynamics is examined
and conclusions are written point wise.Comment: 7 page
Aspects of Horava-Lifshitz cosmology
We review some general aspects of Horava-Lifshitz cosmology. Formulating it
in its basic version, we extract the cosmological equations and we use
observational data in order to constrain the parameters of the theory. Through
a phase-space analysis we extract the late-time stable solutions, and we show
that eternal expansion, and bouncing and cyclic behavior can arise naturally.
Concerning the effective dark energy sector we show that it can describe the
phantom phase without the use of a phantom field. However, performing a
detailed perturbation analysis, we see that Horava-Lifshitz gravity in its
basic version suffers from instabilities. Therefore, suitable generalizations
are required in order for this novel theory to be a candidate for the
description of nature.Comment: 10 pages, 4 figures, invited talk given at the 2nd International
Workshop on Dark Matter, Dark Energy and Matter-Antimatter Assymetry,
National Tsing Hua University, Hsinchu, Taiwan, November 5-6, 201
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