1,261 research outputs found
Gauge Theory of Composite Fermions: Particle-Flux Separation in Quantum Hall Systems
Fractionalization phenomenon of electrons in quantum Hall states is studied
in terms of U(1) gauge theory. We focus on the Chern-Simons(CS) fermion
description of the quantum Hall effect(QHE) at the filling factor
, and show that the successful composite-fermions(CF) theory
of Jain acquires a solid theoretical basis, which we call particle-flux
separation(PFS). PFS can be studied efficiently by a gauge theory and
characterized as a deconfinement phenomenon in the corresponding gauge
dynamics. The PFS takes place at low temperatures, , where
each electron or CS fermion splinters off into two quasiparticles, a fermionic
chargeon and a bosonic fluxon. The chargeon is nothing but Jain's CF, and the
fluxon carries units of CS fluxes. At sufficiently low temperatures , fluxons Bose-condense uniformly and (partly)
cancel the external magnetic field, producing the correlation holes. This
partial cancellation validates the mean-field theory in Jain's CF approach.
FQHE takes place at as a joint effect of (i) integer QHE of
chargeons under the residual field and (ii) Bose condensation of
fluxons. We calculate the phase-transition temperature and the CF
mass. PFS is a counterpart of the charge-spin separation in the t-J model of
high- cuprates in which each electron dissociates into holon and
spinon. Quasiexcitations and resistivity in the PFS state are also studied. The
resistivity is just the sum of contributions of chargeons and fluxons, and
changes its behavior at , reflecting the change of
quasiparticles from chargeons and fluxons at to electrons at
.Comment: 18 pages, 7 figure
Fluctuation effects of gauge fields in the slave-boson t-J model
We present a quantitative study of the charge-spin separation(CSS) phenomenon
in a U(1) gauge theory of the t-J model of high-Tc superconductures. We
calculate the critical temperature of confinement-deconfinement phase
transition below which the CSS takes place.Comment: Latex, 9 pages, 3 figure
Wall and Anti-Wall in the Randall-Sundrum Model and A New Infrared Regularization
An approach to find the field equation solution of the Randall-Sundrum model
with the extra axis is presented. We closely examine the infrared
singularity. The vacuum is set by the 5 dimensional Higgs field. Both the
domain-wall and the anti-domain-wall naturally appear, at the {\it ends} of the
extra compact axis, by taking a {\it new infrared regularization}. The
stability is guaranteed from the outset by the kink boundary condition. A {\it
continuous} (infrared-)regularized solution, which is a truncated {\it Fourier
series} of a {\it discontinuous} solution, is utilized.The ultraviolet-infrared
relation appears in the regularized solution.Comment: 36 pages, 29 eps figure file
Effective gauge field theory of the t-J model in the charge-spin separated state and its transport properties
We study the slave-boson t-J model of cuprates with high superconducting
transition temperatures, and derive its low-energy effective field theory for
the charge-spin separated state in a self-consistent manner. The phase degrees
of freedom of the mean field for hoppings of holons and spinons can be regarded
as a U(1) gauge field, . The charge-spin separation occurs below certain
temperature, , as a deconfinement phenomenon of the dynamics of
. Below certain temperature , the spin-gap
phase develops as the Higgs phase of the gauge-field dynamics, and
acquires a mass . The effective field theory near takes the
form of Ginzburg-Landau theory of a complex scalar field coupled with
, where represents d-wave pairings of spinons. Three
dimensionality of the system is crucial to realize a phase transition at
.
By using this field theory, we calculate the dc resistivity . At , is proportional to . At , it deviates
downward from the -linear behavior as . When the system is near (but not) two dimensional, due to the compactness
of the phase of the field , the exponent deviates from its
mean-field value 1/2 and becomes a nonuniversal quantity which depends on
temperature and doping. This significantly improves the comparison with the
experimental data
Quasi-excitations and superconductivity in the t-J model on a ladder
We study the t-J model on a ladder by using slave-fermion-CP^1 formalism
which is quite useful for study of lightly-doped high-T_c cuprates. By
integrating half of spin variables, we obtain a low-energy effective field
theory whose spin part is nothing but CP^1 sigma model. We especially focus on
dynamics of composite gauge field which determines properties of
quasi-excitations. Value of the coefficient of the topological term strongly
influences gauge dynamics and explaines why properties of quasi-excitations
depend on the number of legs of ladder. We also show that superconductivity
appears as a result of short-range antiferromagnetism and order parameter has
d-wave type symmetry.Comment: Latex, 28 pages and 1 figur
Spin-gap effect on resistivity in the t-J model
We calculate the spin-gap effect on dc resistivity in the t-J model of
high- cuprates by using the Ginzburg-Landau theory coupled with a
gauge field as its effective field theory to get , where is the spin-gap onset temperature. By taking the
compactness of massive gauge field into account, the exponent deviates from
its mean-field value 1/2 and becomes a nonuniversal -dependent quantity,
which improves the correspondence with the experiments.Comment: 4 pages, REVTeX format, 2 eps-figure
Random-mass Dirac fermions in an imaginary vector potential: Delocalization transition and localization length
One dimensional system of Dirac fermions with a random-varying mass is
studied by the transfer-matrix methods which we developed recently. We
investigate the effects of nonlocal correlation of the spatial-varying Dirac
mass on the delocalization transition. Especially we numerically calculate both
the "typical" and "mean" localization lengths as a function of energy and the
correlation length of the random mass. To this end we introduce an imaginary
vector potential as suggested by Hatano and Nelson and solve the eigenvalue
problem. Numerical calculations are in good agreement with the results of the
analytical calculations.Comment: 4 page
Critical phenomena of thick branes in warped spacetimes
We have investigated the effects of a generic bulk first-order phase
transition on thick Minkowski branes in warped geometries. As occurs in
Euclidean space, when the system is brought near the phase transition an
interface separating two ordered phases splits into two interfaces with a
disordered phase in between. A remarkable and distinctive feature is that the
critical temperature of the phase transition is lowered due to pure geometrical
effects. We have studied a variety of critical exponents and the evolution of
the transverse-traceless sector of the metric fluctuations.Comment: revtex4, 4 pages, 4 figures, some comments added, typos corrected,
published in PR
Effects of cariprazine on extracellular levels of glutamate, GABA, dopamine, noradrenaline and serotonin in the medial prefrontal cortex in the rat phencyclidine model of schizophrenia studied by microdialysis and simultaneous recordings of locomotor activity
Aberrant glutamatergic, dopaminergic, and GABAergic neurotransmission has been implicated in schizophrenia. Cariprazine reverses the behavioral effects observed in the rat phencyclidine (PCP)-induced model of schizophrenia; however, little is known about its in vivo neurochemistry. The study aims to compare the effects of cariprazine and aripiprazole on PCP-induced changes in the extracellular levels of glutamate, dopamine, serotonin, noradrenaline, and GABA in the rat medial prefrontal cortex (mPFC), and on locomotor activation. Microdialysis was performed in awake rats with probes placed into the mPFC. Rats (n = 7/group) received vehicle (saline), cariprazine (0.05, 0.2, or 0.8 mg/kg), or aripiprazole (3 or 20 mg/kg) via gavage. After 60 min, 5 mg/kg PCP was administered intraperitoneally (i.p.). Samples were taken before drug administration, during pretreatment, and after PCP injection. Locomotor activity recording and microdialysis sampling occurred simultaneously. PCP treatment increased extracellular levels of all the neurotransmitters tested except GABA, for which there were no significant changes. Cariprazine and aripiprazole dose-dependently inhibited the PCP-induced increases of tested neurotransmitters. Overall effects were significant for higher cariprazine doses and both aripiprazole doses for glutamate and noradrenaline, for higher cariprazine doses and 20 mg/kg aripiprazole for dopamine, and for 0.8 mg/kg cariprazine and 20 mg/kg aripiprazole for serotonin and locomotor activity. Both cariprazine and aripiprazole dose-dependently attenuated PCP-induced hyperlocomotion and acute increases in glutamate, dopamine, noradrenaline, and serotonin levels in the mPFC; cariprazine was approximately 5-fold more potent than aripiprazole
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