5,596 research outputs found
The Stochastic Quantization Method in Phase Space and a New Gauge Fixing Procedure
We study the stochastic quantization of the system with first class
constraints in phase space. Though the Langevin equations of the canonical
variables are defined without ordinary gauge fixing procedure, gauge fixing
conditions are automatically selected and introduced by imposing stochastic
consistency conditions upon the first class constraints. Then the equilibrium
solution of the Fokker-Planck equation is identical with corresponding path
integral distribution.Comment: 18 pages (Plain TeX), CHIBA-EP-7
(D+1)-Dimensional Formulation for D-Dimensional Constrained Systems
D-dimensional constrained systems are studied with stochastic Lagrangian
and\break Hamiltonian. It is shown that stochastic consistency conditions are
second class constraints and Lagrange multiplier fields can be determined in
(D+1)-dimensional canonical formulation. The Langevin equations for the
constrained system are obtained as Hamilton's equations of motion where
conjugate momenta play a part of noise fields.Comment: 10 pages (Plain TeX), CHIBA-EP-58-Re
Dynamical Symmetry Breaking on Langevin Equation : Nambu Jona-Lasinio Model
In order to investigate dynamical symmetry breaking, we study
NambuJona-Lasinio model in the large-N limit in the stochastic
quantization method. Here in order to solve Langevin equation, we impose
specified initial conditions and construct ``effective Langevin equation'' in
the large-N limit and give the same non-perturbative results as path-integral
approach gives. Moreover we discuss stability of vacuum by means of ``effective
potential''.Comment: 12 pages (Plain TeX), 7 figures(not included, sorry!), CHIBA-EP-6
Eternally accelerating spacelike braneworld cosmologies
We construct an eternally inflating spacelike brane world model. If the space
dimension of the brane is three (SM2) or six (SM5) for M theory or four (SD3)
for superstring theory, a time-dependent -form field would supply a constant
energy density and cause exponentially expansion of the spacelike brane. In
these cases, the hyperbolic space perpendicular to the brane would not vary in
size. In the other cases, however, the extra space would vary in size.Comment: 8 pages, Mod. Phys. Lett. A Vol.21, No.40(2006) 2989-299
Ferromagnetic insulating phase in Pr{1-x}Ca{x}MnO3
A ferromagnetic insulating (FM-I) state in Pr0.75Ca0.25MnO3 has been studied
by neutron scattering experiment and theoretical calculation. The insulating
behavior is robust against an external magnetic field, and is ascribed to
neither the phase separation between a ferromagnetic metallic (FM-M) phase and
a non-ferromagnetic insulating one, nor the charge ordering. We found that the
Jahn-Teller type lattice distortion is much weaker than PrMnO3 and the magnetic
interaction is almost isotropic. These features resembles the ferromagnetic
metallic state of manganites, but the spin exchange interaction J is much
reduced compared to the FM-M state. The theoretical calculation based on the
staggered type orbital order well reproduces several features of the spin and
orbital state in the FM-I phase.Comment: REVTeX4, 10 pages, 9 figure
Specific Heat and Superfluid Density for Possible Two Different Superconducting States in NaxCoO2.yH2O
Several thermodynamic measurements for the cobaltate superconductor,
NaxCoO2.yH2O, have so far provided results inconsistent with each other. In
order to solve the discrepancies, we microscopically calculate the temperature
dependences of specific heat and superfluid density for this superconductor. We
show that two distinct specific-heat data from Oeschler et al. and Jin et al.
are reproduced, respectively, for the extended s-wave state and the p-wave
state. Two different superfluid-density data are also reproduced for each case.
These support our recent proposal of possible two different pairing states in
this material. In addition, we discuss the experimentally proposed large
residual Sommerfeld coefficient and extremely huge effective carrier mass.Comment: 5 pages, 4 figures, Submitted to J. Phys. Soc. Jp
Roles of Bond Alternation in Magnetic Phase Diagram of RMnO3
In order to investigate nature of the antiferromagnetic structures in
perovskite RMnO3, we study a Heisenberg J1-J2 model with bond alternation using
analytical and numerical approaches. The magnetic phase diagram which includes
incommensurate spiral states and commensurate collinear states is reproduced.
We discuss that the magnetic structure with up-up-down-down spin configuration
(E-type structure) and the ferroelectricity emerge cooperatively to stabilize
this phase. Magnetoelastic couplings are crucial to understand the magnetic and
electric phase diagram of RMnO3.Comment: 5 pages, 6 figure
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