2,870 research outputs found
Magnetic properties of the spin-1/2 XXZ model on the Shastry-Sutherland lattice: Effect of long-range interactions
We study magnetic properties of the Ising-like XXZ model on the
Shastry-Sutherland lattices with long-range interactions, using the quantum
Monte Carlo method. This model shows magnetization plateau phases at one-half
and one-third of the saturation magnetization when additional couplings are
considered. We investigate the finite temperature transition to one-half and
one-third plateau phases. The obtained results suggest that the former case is
of the first order and the latter case is of the second order. We also find
that the system undergoes two successive transitions with the 2D Ising model
universality, although there is a single phase transition in the Ising limit
case. Finally, we estimate the coupling ratio to explain the magnetization
process observed in Comment: 5 pages, 6 figure
Double- Order in a Frustrated Random Spin System
We use the three-dimensional Heisenberg model with site randomness as an
effective model of the compound Sr(FeMn)O. The model consists
of two types of ions that correspond to Fe and Mn ions. The nearest-neighbor
interactions in the ab-plane are antiferromagnetic. The nearest-neighbor
interactions along the c-axis between Fe ions are assumed to be
antiferromagnetic, whereas other interactions are assumed to be ferromagnetic.
From Monte Carlo simulations, we confirm the existence of the
double- ordered phase characterized by two wave numbers,
and . We also identify the spin ordering pattern in
the double- ordered phase.Comment: 5pages, 3figure
Non-Gaussianity analysis of GW background made by short-duration burst signals
We study an observational method to analyze non-Gaussianity of a
gravitational wave (GW) background made by superposition of weak burst signals.
The proposed method is based on fourth-order correlations of data from four
detectors, and might be useful to discriminate the origin of a GW background.
With a formulation newly developed to discuss geometrical aspects of the
correlations, it is found that the method provides us with linear combinations
of two interesting parameters, I_2 and V_2 defined by the Stokes parameters of
individual GW burst signals. We also evaluate sensitivities of specific
detector networks to these parameters.Comment: 18 pages, to appear in PR
Global network structure of dominance hierarchy of ant workers
Dominance hierarchy among animals is widespread in various species and
believed to serve to regulate resource allocation within an animal group.
Unlike small groups, however, detection and quantification of linear hierarchy
in large groups of animals are a difficult task. Here, we analyse
aggression-based dominance hierarchies formed by worker ants in Diacamma sp. as
large directed networks. We show that the observed dominance networks are
perfect or approximate directed acyclic graphs, which are consistent with
perfect linear hierarchy. The observed networks are also sparse and random but
significantly different from networks generated through thinning of the perfect
linear tournament (i.e., all individuals are linearly ranked and dominance
relationship exists between every pair of individuals). These results pertain
to global structure of the networks, which contrasts with the previous studies
inspecting frequencies of different types of triads. In addition, the
distribution of the out-degree (i.e., number of workers that the focal worker
attacks), not in-degree (i.e., number of workers that attack the focal worker),
of each observed network is right-skewed. Those having excessively large
out-degrees are located near the top, but not the top, of the hierarchy. We
also discuss evolutionary implications of the discovered properties of
dominance networks.Comment: 5 figures, 2 tables, 4 supplementary figures, 2 supplementary table
Uniqueness of canonical tensor model with local time
Canonical formalism of the rank-three tensor model has recently been
proposed, in which "local" time is consistently incorporated by a set of first
class constraints. By brute-force analysis, this paper shows that there exist
only two forms of a Hamiltonian constraint which satisfies the following
assumptions: (i) A Hamiltonian constraint has one index. (ii) The kinematical
symmetry is given by an orthogonal group. (iii) A consistent first class
constraint algebra is formed by a Hamiltonian constraint and the generators of
the kinematical symmetry. (iv) A Hamiltonian constraint is invariant under time
reversal transformation. (v) A Hamiltonian constraint is an at most cubic
polynomial function of canonical variables. (vi) There are no disconnected
terms in a constraint algebra. The two forms are the same except for a slight
difference in index contractions. The Hamiltonian constraint which was obtained
in the previous paper and behaved oddly under time reversal symmetry can
actually be transformed to one of them by a canonical change of variables. The
two-fold uniqueness is shown up to the potential ambiguity of adding terms
which vanish in the limit of pure gravitational physics.Comment: 21 pages, 12 figures. The final result unchanged. Section 5 rewritten
for clearer discussions. The range of uniqueness commented in the final
section. Some other minor correction
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