31,585 research outputs found
Semiclassical description of spin ladders
The Heisenberg spin ladder is studied in the semiclassical limit, via a
mapping to the nonlinear model. Different treatments are needed if the
inter-chain coupling is small, intermediate or large. For intermediate
coupling a single nonlinear model is used for the ladder. Its predicts
a spin gap for all nonzero values of if the sum of the spins
of the two chains is an integer, and no gap otherwise. For small , a better
treatment proceeds by coupling two nonlinear sigma models, one for each chain.
For integer , the saddle-point approximation predicts a sharp drop
in the gap as increases from zero. A Monte-Carlo simulation of a spin 1
ladder is presented which supports the analytical results.Comment: 8 pages, RevTeX 3.0, 4 PostScript figure
Quantum Heisenberg Chain with Long-Range Ferromagnetic Interactions at Low Temperature
A modified spin-wave theory is applied to the one-dimensional quantum
Heisenberg model with long-range ferromagnetic interactions. Low-temperature
properties of this model are investigated. The susceptibility and the specific
heat are calculated; the relation between their behaviors and strength of the
long-range interactions is obtained. This model includes both the
Haldane-Shastry model and the nearest-neighbor Heisenberg model; the
corresponding results in this paper are in agreement with the solutions of both
the models. It is shown that there exists an ordering transition in the region
where the model has longer-range interactions than the HS model. The critical
temperature is estimated.Comment: 17 pages(LaTeX REVTeX), 1 figure appended (PostScript), Technical
Report of ISSP A-274
Quantum Spin Chains and Riemann Zeta Function with Odd Arguments
Riemann zeta function is an important object of number theory. It was also
used for description of disordered systems in statistical mechanics. We show
that Riemann zeta function is also useful for the description of integrable
model. We study XXX Heisenberg spin 1/2 anti-ferromagnet. We evaluate a
probability of formation of a ferromagnetic string in the anti-ferromagnetic
ground state in thermodynamics limit. We prove that for short strings the
probability can be expressed in terms of Riemann zeta function with odd
arguments.Comment: LaTeX, 7 page
Entropy production by Q-ball decay for diluting long-lived charged particles
The cosmic abundance of a long-lived charged particle such as a stau is
tightly constrained by the catalyzed big bang nucleosynthesis. One of the ways
to evade the constraints is to dilute those particles by a huge entropy
production. We evaluate the dilution factor in a case that non-relativistic
matter dominates the energy density of the universe and decays with large
entropy production. We find that large Q balls can do the job, which is
naturally produced in the gauge-mediated supersymmetry breaking scenario.Comment: 8 pages, 1 figur
Exact results for the 1D interacting mixed Bose-Fermi gas
The exact solution of the 1D interacting mixed Bose-Fermi gas is used to
calculate ground-state properties both for finite systems and in the
thermodynamic limit. The quasimomentum distribution, ground-state energy and
generalized velocities are obtained as functions of the interaction strength
both for polarized and non-polarized fermions. We do not observe any demixing
instability of the system for repulsive interactions.Comment: 12 pages, 4 figures, better comparison with hydrodynamic approach,
typos corrected, references added, improved figure
The Evolution of Globular Clusters in the Galaxy
We investigate the evolution of globular clusters using N-body calculations
and anisotropic Fokker-Planck (FP) calculations. The models include a mass
spectrum, mass loss due to stellar evolution, and the tidal field of the parent
galaxy. Recent N-body calculations have revealed a serious discrepancy between
the results of N-body calculations and isotropic FP calculations. The main
reason for the discrepancy is an oversimplified treatment of the tidal field
employed in the isotropic FP models. In this paper we perform a series of
calculations with anisotropic FP models with a better treatment of the tidal
boundary and compare these with N-body calculations. The new tidal boundary
condition in our FP model includes one free parameter. We find that a single
value of this parameter gives satisfactory agreement between the N-body and FP
models over a wide range of initial conditions.
Using the improved FP model, we carry out an extensive survey of the
evolution of globular clusters over a wide range of initial conditions varying
the slope of the mass function, the central concentration, and the relaxation
time. The evolution of clusters is followed up to the moment of core collapse
or the disruption of the clusters in the tidal field of the parent galaxy. In
general, our model clusters, calculated with the anisotropic FP model with the
improved treatment for the tidal boundary, live longer than isotropic models.
The difference in the lifetime between the isotropic and anisotropic models is
particularly large when the effect of mass loss via stellar evolution is rather
significant. On the other hand the difference is small for relaxation-
dominated clusters which initially have steep mass functions and high central
concentrations.Comment: 36 pages, 11 figures, LaTeX; added figures and tables; accepted by
Ap
Fundamental Cycle of a Periodic Box-Ball System
We investigate a soliton cellular automaton (Box-Ball system) with periodic
boundary conditions. Since the cellular automaton is a deterministic dynamical
system that takes only a finite number of states, it will exhibit periodic
motion. We determine its fundamental cycle for a given initial state.Comment: 28 pages, 6 figure
Spin-Wave Theory of the Spiral Phase of the t-J Model
A graded H.P,realization of the SU(2|1) algebra is proposed.A spin-wave
theory with a condition that the sublattice magnetization is zero is
discussed.The long-range spiral phase is investigated.The spin-spin correlator
is calculated.Comment: 17 page
Excitation Spectrum of Antiferromagnetic Chains
The dynamical structure factor of the antiferromagnetic
Heisenberg chain with length 20 at zero temperature is calculated. The lowest
energy states have the delta-function peak at the region . At the lowest energy states are the lower-edge
of the continuum of the scattering state, the strength of which decreases for
large systems. This gives a reasonable explanation for the experimental fact
that no clear peak is observed at the region . This situation is more
apparent for valence-bond solid state. On the contrary for
antiferromagnetic Heisenberg chain the lowest energy states are always the edge
of the continuum.Comment: 14pages, Revtex 3.0, No.279
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