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 $\nu=p/(2pq\pm 1)$, 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, $T \leq T_{\rm PFS}$, 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 $2q$ units of CS fluxes. At sufficiently low temperatures $T \leq T_{\rm BC} (< T_{\rm PFS})$, 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 $T < T_{\rm BC}$ as a joint effect of (i) integer QHE of chargeons under the residual field $\Delta B$ and (ii) Bose condensation of fluxons. We calculate the phase-transition temperature $T_{\rm PFS}$ and the CF mass. PFS is a counterpart of the charge-spin separation in the t-J model of high-$T_{\rm c}$ 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 $\rho_{xx}$ changes its behavior at $T = T_{\rm PFS}$, reflecting the change of quasiparticles from chargeons and fluxons at $T < T_{\rm PFS}$ to electrons at $T_{\rm PFS} < T$.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 $S^1/Z_2$ 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, $A_i$. The charge-spin separation occurs below certain temperature, $T_{\rm CSS}$, as a deconfinement phenomenon of the dynamics of $A_i$. Below certain temperature $T_{\rm SG} (< T_{\rm CSS})$, the spin-gap phase develops as the Higgs phase of the gauge-field dynamics, and $A_i$ acquires a mass $m_A$. The effective field theory near $T_{\rm SG}$ takes the form of Ginzburg-Landau theory of a complex scalar field $\lambda$ coupled with $A_i$, where $\lambda$ represents d-wave pairings of spinons. Three dimensionality of the system is crucial to realize a phase transition at $T_{\rm SG}$. By using this field theory, we calculate the dc resistivity $\rho$. At $T > T_{\rm SG}$, $\rho$ is proportional to $T$. At $T < T_{\rm SG}$, it deviates downward from the $T$-linear behavior as $\rho \propto T \{1 -c(T_{\rm SG}-T)^d \}$. When the system is near (but not) two dimensional, due to the compactness of the phase of the field $\lambda$, the exponent $d$ 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-$T_{\rm c}$ cuprates by using the Ginzburg-Landau theory coupled with a gauge field as its effective field theory to get $\rho(T) \propto T \{1-c\:(T^* -T)^d \}$, where $T^*$ is the spin-gap onset temperature. By taking the compactness of massive gauge field into account, the exponent $d$ deviates from its mean-field value 1/2 and becomes a nonuniversal $T$-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