18,324 research outputs found
Critical Properties of the transition between the Haldane phase and the large-D phase of the spin-1/2 ferromagnetic-antiferromagnetic Heisenberg chain with on-site anisotropy"
We analytically study the ground-state quantum phase transition between the
Haldane phase and the large- (LD) phase of the
ferromagnetic-antiferromagnetic alternating Heisenberg chain with on-site
anisotropy. We transform this model into a generalized version of the
alternating antiferromagnetic Heisenberg model with anisotropy. In the
transformed model, the competition between the transverse and longitudinal bond
alternations yields the Haldane-LD transition. Using the bosonization method,
we show that the critical exponents vary continuously on the Haldane-LD
boundary. Our scaling relations between critical exponents very well explains
the numerical results by Hida.Comment: text 12 pages (Plain TeX), LaTeX sourse files of a table and a figure
on reques
Non-Collinear Magnetic Phases of a Triangular-Lattice Antiferromagnet and Doped CuFeO
We obtain the non-collinear ground states of a triangular-lattice
antiferromagnet with exchange interactions up to third nearest neighbors as a
function of the single-ion anisotropy . At a critical value of , the
collinear \uudd phase transforms into a complex non-collinear phase with
odd-order harmonics of the fundamental ordering wavevector \vQ . The observed
elastic peaks at 2\pi \vx -\vQ in both Al- and Ga- doped CuFeO are
explained by a "scalene" distortion of the triangular lattice produced by the
repulsion of neighboring oxygen atoms.Comment: 4 pages 3 figures, accepted for publication by Phys. Rev. B Rapid
communication
Three-Body-Cluster Effects on Lambda Single-Particle Energies in _{Lambda}^{17}O and_{Lambda}^{41}Ca
A method for a microscopic description of Lambda hypernuclei is formulated in
the framework of the unitary-model-operator approach. A unitarily transformed
hamiltonian is introduced and given in a cluster expansion form. The structure
of three-body-cluster terms are discussed especially on the Lambda
single-particle energy. The Lambda single-particle energies including the
three-body-cluster contributions are calculated for the 0s_{1/2}, 0p_{3/2} and
0p_{1/2} states in_{Lambda}^{17}O, and for the 0s_{1/2}, 0p_{3/2}, 0p_{1/2},
0d_{5/2}, 0d_{3/2} and 1s_{1/2} states in_{Lambda}^{41}Ca, using the Nijmegen
soft-core (NSC), NSC97a-f, the Juelich A (J A) and J B hyperon-nucleon
interactions. It is indicated that the three-body-cluster terms bring about
sizable effects in the magnitudes of the Lambda single-particle energies, but
hardly affect the Lambda spin-orbit splittings.Comment: LaTeX 19 pages including 7 figures, ptptex.sty is use
Shell structures in oxygen isotopes described with modern nucleon-nucleon interactions
Shell structures in the N\simeq Z nucleus ^{17}O and the neutron-rich oxygen
isotopes ^{23}O and ^{25}O are microscopically described by calculating
single-particle energies with modern nucleon-nucleon interactions within the
framework of the unitary-model-operator approach. It is found that the effect
of three-body cluster terms on the single-particle energy is more important in
^{23}O and ^{25}O than ^{17}O.Comment: 5 pages, 1 figure, Talk at the International Symposium on "A New Era
of Nuclear Structure Physics (NENS03)", 19-22 Nov. 2003, Niigata, Japa
Charge-dependent calculations of single-particle energies in nuclei around ^{16}O with modern nucleon-nucleon interactions
The binding energies of the ground states and several excited states related
to single-particle and -hole states in nuclei around ^{16}O are calculated
taking charge dependence into account. Effective interactions on the particle
basis are constructed from modern charge-dependent nucleon-nucleon interactions
and the Coulomb force within the framework of the unitary-model-operator
approach. Single-particle (-hole) energies are obtained from the energy
differences of the binding energies between a particle (hole) state in ^{17}O
or ^{17}F (^{15}N or ^{15}O) and the ground state of ^{16}O. The resultant
spin-orbit splittings are small for the hole state and large for the particle
state in comparison with the experimental values though the differences between
the experimental and calculated values are not very large. The charge
dependence of the calculated single-particle energies for the ground states are
in good agreement with the experimental values. Furthermore, the Thomas-Ehrman
shift due to the Coulomb force for the 1s_{1/2} states in ^{17}O and ^{17}F can
be observed.Comment: 14 pages, 12 figures, submitted to Phys. Rev.
Ground-state and single-particle energies of nuclei around ^{16}O, ^{40}Ca, and ^{56}Ni from realistic nucleon-nucleon forces
We perform ab initio calculations for nuclei around ^{16}O, ^{40}Ca, and
^{56}Ni using realistic nucleon-nucleon forces. In particular, ^{56}Ni is
computed as the heaviest nucleus in this kind of ab initio calculation.
Ground-state and single-particle energies including three-body-cluster effects
are obtained within the framework of the unitary-model-operator approach. It is
shown that the CD-Bonn nucleon-nucleon potential gives quite good results close
to the experimental values for all nuclei in the present work.Comment: 4 pages, 4 figures; accepted for publication in Physical Review
Letter
Irregular conformal blocks, with an application to the fifth and fourth Painlev\'e equations
We develop the theory of irregular conformal blocks of the Virasoro algebra.
In previous studies, expansions of irregular conformal blocks at regular
singular points were obtained as degeneration limits of regular conformal
blocks; however, such expansions at irregular singular points were not clearly
understood. This is because precise definitions of irregular vertex operators
had not been provided previously. In this paper, we present precise definitions
of irregular vertex operators of two types and we prove that one of our vertex
operators exists uniquely. Then, we define irregular conformal blocks with at
most two irregular singular points as expectation values of given irregular
vertex operators. Our definitions provide an understanding of expansions of
irregular conformal blocks and enable us to obtain expansions at irregular
singular points.
As an application, we propose conjectural formulas of series expansions of
the tau functions of the fifth and fourth Painlev\'e equations, using
expansions of irregular conformal blocks at an irregular singular point.Comment: 26 page
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