9,913 research outputs found
Field-induced long-range order in the S=1 antiferromagnetic chain
The quasi-one dimensional S=1 antiferromagnet in magnetic field H is
investigated with the exact diagonalization of finite chains and the mean field
approximation for the interchain interaction. In the presence of the single-ion
anisotropy D, the full phase diagram in the plane is presented for H
\parallel D and H \perp D. The shape of the field-induced long-range ordered
phase is revealed to be quite different between the two cases, as observed in
the recent experiment of NDMAP. The estimated ratio of the interchain and
intrachain couplings of NDMAP (J'/J ~ 10^{-3}) is consistent with the neutron
scattering measurement.Comment: 4 pages, Revtex, with 6 eps figure
How Do Nonlinear Voids Affect Light Propagation ?
Propagation of light in a clumpy universe is examined. As an inhomogeneous
matter distribution, we take a spherical void surrounded by a dust shell where
the ``lost mass'' in the void is compensated by the shell. We study how the
angular-diameter distance behaves when such a structure exists. The
angular-diameter distance is calculated by integrating the Raychaudhuri
equation including the shear. An explicit expression for the junction condition
for the massive thin shell is calculated. We apply these results to a dust
shell embedded in a Friedmann universe and determine how the distance-redshift
relation is modified compared with that in the purely Friedmann universe. We
also study the distribution of distances in a universe filled with voids. We
show that the void-filled universe gives a larger distance than the FRW
universe by at if the size of the void is of the
Horizon radius.Comment: To appear in Prog. Theor. Phys. 10
Critical exponent in the magnetization curve of quantum spin chains
The ground state magnetization curve around the critical magnetic field
of quantum spin chains with the spin gap is investigated. We propose a size
scaling method to estimate the critical exponent defined as from finite cluster calculation. The applications of the
method to the S=1 antiferromagnetic chain and S=1/2 bond alternating chain lead
to a common conclusion . The same result is derived for both edges
of the magnetization plateau of the S=3/2 antiferromagnetic chain with the
single ion anisotropy.Comment: 4 pages, Revtex, with 4 eps figure
Metamagnetism of antiferromagnetic XXZ quantum spin chains
The magnetization process of the one-dimensional antiferromagnetic Heisenberg
model with the Ising-like anisotropic exchange interaction is studied by the
exact diagonalization technique. It results in the evidence of the first-order
spin flop transition with a finite magnetization jump in the N\'eel ordered
phase for . It implies that the S=1/2 chain is an exceptional case
where the metamagnetic transition becomes second-order due to large quantum
fluctuations.Comment: 4 pages, Revtex, with 6 eps figure
Field induced long-range-ordering in an S=1 quasi-one-dimensional Heisenberg antiferromagnet
We have measured the heat capacity and magnetization of the spin one
one-dimensional Heisenberg antiferromagnet NDMAP and constructed a magnetic
field versus temperature phase diagram. We found a field induced long-range
magnetic ordering. We have been successful in explaining the phase diagram
theoretically.Comment: 6 pages, 18 figure
Static Gravitational Global Monopoles
Static solutions in spherical symmetry are found for gravitating global
monopoles. Regular solutions lacking a horizon are found for , where is the scale of symmetry breaking. Apparently
regular solutions with a horizon are found for 1/\sqrt{8\pi} \le \eta \alt
\sqrt{3/8\pi}. Though they have a horizon, they are not Schwarzschild. The
solution for is argued to have a horizon at infinity.
The failure to find static solutions for
is consistent with findings that topological inflation begins at .Comment: 4 pages, 6 figure
Relativistic particle acceleration in an electronâpositron plasma with a relativistic electron beam
Results from threeâdimensional electromagnetic particle simulations of an electronâpositron plasma with a relativistic electron beam (Îł=2) are presented. As part of the initial conditions, a poloidal magnetic field is specified, consistent with the current carried by the beam electrons. The beam undergoes pinching oscillations due to the pressure imbalance. A transverse twoâstream instability is excited with large helical perturbations. In the process, background electrons and positrons are heated and accelerated up to relativistic energy levels. Only background electrons are accelerated farther along the z direction due the synergetic effects by both the damped transverse mode and the accompanying electrostatic waves caused by the breakdown of the helical perturbations. © 1994 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70513/2/PHPAEN-1-12-4114-1.pd
Quantum Restoration of the U(1)_Y Symmetry in Dynamically Broken SUSY-GUT's
We propose a supersymmetric hypercolor SU(3)_H gauge theory interacting
strongly at the grand unification scale, in which the hyperquark condensation
breaks SU(5)_GUT down to SU(3)_C x SU(2)_L without unbroken U(1)_Y at the
classical level. However, we show that the broken U(1)_Y symmetry is restored
by quantum mechanical effects and hence there remains the standard-model gauge
symmetry at the electroweak scale. The dynamics of the strong interactions also
produces naturally a pair of massless Higgs doublets. In addition to these
Higgs doublets, we have a pair of massless singlets which contributes to the
renormalization-group equations of gauge coupling constants and hence affects
the GUT unification. We discuss a simple solution to this problem.Comment: 12 pages, LaTeX, 1 Postscript figur
Critical properties of S=1/2 Heisenberg ladders in magnetic fields
The critical properties of the Heisenberg two-leg ladders are
investigated in a magnetic field. Combining the exact diagonalization method
and the finite-size-scaling analysis based on conformal field theory, we
calculate the critical exponents of spin correlation functions numerically. For
a strong interchain coupling, magnetization dependence of the critical
exponents shows characteristic behavior depending on the sign of the interchain
coupling. We also calculate the critical exponents for the Heisenberg
two-leg ladder with a diagonal interaction, which is thought as a model
Hamiltonian of the organic spin ladder compound
. Numerical results are compared with
experimental results of temperature dependence of the NMR relaxation rate
.Comment: REVTeX, 10 pages, 8 figures, accepted for Phys. Rev.
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