6,680 research outputs found
Parisi States in a Heisenberg Spin-Glass Model in Three Dimensions
We have studied low-lying metastable states of the Heisenberg model
in two () and three () dimensions having developed a hybrid genetic
algorithm. We have found a strong evidence of the occurrence of the Parisi
states in but not in . That is, in lattices, there exist
metastable states with a finite excitation energy of for
, and energy barriers between the ground state and
those metastable states are with in
but with in . We have also found droplet-like
excitations, suggesting a mixed scenario of the replica-symmetry-breaking
picture and the droplet picture recently speculated in the Ising SG model.Comment: 4 pages, 6 figure
Apparent Clustering of Intermediate-redshift Galaxies as a Probe of Dark Energy
We show the apparent redshift-space clustering of galaxies in redshift range
of 0.2--0.4 provides surprisingly useful constraints on dark energy component
in the universe, because of the right balance between the density of objects
and the survey depth. We apply Fisher matrix analysis to the the Luminous Red
Galaxies (LRGs) in the Sloan Digital Sky Survey (SDSS), as a concrete example.
Possible degeneracies in the evolution of the equation of state (EOS) and the
other cosmological parameters are clarified.Comment: 5 pages, 3 figures, Phys.Rev.Lett., replaced with the accepted
versio
Three Dimensional Heisenberg Spin Glass Models with and without Random Anisotropy
We reexamine the spin glass (SG) phase transition of the Heisenberg
models with and without the random anisotropy in three dimensions ()
using complementary two methods, i.e., (i) the defect energy method and (ii)
the Monte Carlo method. We reveal that the conventional defect energy method is
not convincing and propose a new method which considers the stiffness of the
lattice itself. Using the method, we show that the stiffness exponent
has a positive value () even when . Considering the
stiffness at finite temperatures, we obtain the SG phase transition temperature
of for . On the other hand, a large scale MC
simulation shows that, in contrary to the previous results, a scaling plot of
the SG susceptibility for is obtained using almost the
same transiton temperature of . Hence we believe that
the SG phase transition occurs in the Heisenberg SG model in .Comment: 15 pages, 9 figures, to be published in J. Phys.
Phase diagram of a dilute ferromagnet model with antiferromagnetic next-nearest-neighbor interactions
We have studied the spin ordering of a dilute classical Heisenberg model with
spin concentration , and with ferromagnetic nearest-neighbor interaction
and antiferromagnetic next-nearest-neighbor interaction . Magnetic
phases at absolute zero temperature are determined examining the
stiffness of the ground state, and those at finite temperatures are
determined calculating the Binder parameter and the spin correlation
length . Three ordered phases appear in the phase diagram: (i) the
ferromagnetic (FM) phase; (ii) the spin glass (SG) phase; and (iii) the mixed
(M) phase of the FM and the SG. Near below the ferromagnetic threshold , a reentrant SG transition occurs. That is, as the temperature is decreased
from a high temperature, the FM phase, the M phase and the SG phase appear
successively. The magnetization which grows in the FM phase disappears in the
SG phase. The SG phase is suggested to be characterized by ferromagnetic
clusters. We conclude, hence, that this model could reproduce experimental
phase diagrams of dilute ferromagnets FeAu and EuSrS.Comment: 9 pages, 23 figure
Ground-State Properties of a Heisenberg Spin Glass Model with a Hybrid Genetic Algorithm
We developed a genetic algorithm (GA) in the Heisenberg model that combines a
triadic crossover and a parameter-free genetic algorithm. Using the algorithm,
we examined the ground-state stiffness of the Heisenberg model in three
dimensions up to a moderate size range. Results showed the stiffness constant
of in the periodic-antiperiodic boundary condition method and that
of in the open-boundary-twist method. We considered the
origin of the difference in between the two methods and suggested that
both results show the same thing: the ground state of the open system is stable
against a weak perturbation.Comment: 11 pages, 5 figure
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