1,266 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
Field Quantization in 5D Space-Time with Z-parity and Position/Momentum Propagator
Field quantization in 5D flat and warped space-times with Z-parity is
comparatively examined. We carefully and closely derive 5D
position/momentum(P/M) propagators. Their characteristic behaviours depend on
the 4D (real world) momentum in relation to the boundary parameter () and
the bulk curvature (\om). They also depend on whether the 4D momentum is
space-like or time-like. Their behaviours are graphically presented and the
Z symmetry, the "brane" formation and the singularities are examined. It is
shown that the use of absolute functions is important for properly treating the
singular behaviour. The extra coordinate appears as a {\it directed} one like
the temperature. The problem, which is an important consistency
check of the bulk-boundary system, is solved {\it without} the use of
KK-expansion. The relation between P/M propagator (a closed expression which
takes into account {\it all} KK-modes) and the KK-expansion-series propagator
is clarified. In this process of comparison, two views on the extra space
naturally come up: orbifold picture and interval (boundary) picture.
Sturm-Liouville expansion (a generalized Fourier expansion) is essential there.
Both 5D flat and warped quantum systems are formulated by the Dirac's bra and
ket vector formalism, which shows the warped model can be regarded as a {\it
deformation} of the flat one with the {\it deformation parameter} \om. We
examine the meaning of the position-dependent cut-off proposed by
Randall-Schwartz.Comment: 44 figures, 22(fig.)+41 pages, to be published in Phys.Rev.D, Fig.4
is improve
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
CP Violation from a Higher Dimensional Model
It is shown that Randall-Sundrum model has the EDM term which violates the
CP-symmetry. The comparison with the case of Kaluza-Klein theory is done. The
chiral property, localization, anomaly phenomena are examined. We evaluate the
bulk quantum effect using the method of the induced effective action. This is a
new origin of the CP-violation.Comment: 15pages, Proc. of Int. Workshop on "Neutrino Masses and
Mixings"(Dec.17-19,2006,Univ.of Shizuoka,Japan
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
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
Quarks, Gluons and Frustrated Antiferromagnets
The Contractor Renormalization Group method (CORE) is used to establish the
equivalence of various Hamiltonian free fermion theories and a class of
generalized frustrated antiferromagnets. In particular, after a detailed
discussion of a simple example, it is argued that a generalized frustrated
SU(3) antiferromagnet whose single-site states have the quantum numbers of
mesons and baryons is equivalent to a theory of free massless quarks.
Furthermore, it is argued that for slight modification of the couplings which
define the frustrated antiferromagnet Hamiltonian, the theory becomes a theory
of quarks interacting with color gauge-fields.Comment: 21 pages, Late
Bad expression influences time to androgen escape in prostate cancer
<b>OBJECTIVE</b>: To assess the role of selected downstream Bcl-2 family members (Bad, Bax, Bcl-2 and Bcl-xL) in the development of androgen-independent prostate cancer (AIPC), as androgen-deprivation therapy is the treatment of choice in advanced prostate cancer, yet patients generally relapse and progress to an AI state within 18â24 months.
<b>PATIENTS, MATERIALS AND METHODS</b>: The patient cohort was established by retrospectively selecting patients with prostate cancer who had an initial response to androgen-deprivation therapy, but subsequently relapsed with AIPC. In all, 58 patients with prostate cancer were included with matched androgen-dependent (AD) and AI prostate tumours available for immunohistochemical analysis; two independent observers using a weighted-histoscore method scored the staining. Changes in Bad, Bax, Bcl-2 and Bcl-xL expression during transition to AIPC were evaluated and then correlated to known clinical variables.
<b>RESULTS</b>: High Bad expression in AD tumours was associated with an increased time to biochemical relapse (<i>P</i> = 0.007) and a trend towards improved overall survival (<i>P</i> = 0.053). There were also trends towards a decrease in Bad (<i>P</i> = 0.068) and Bax (<i>P</i> = 0.055) expression with progression to AIPC. There were no significant results for Bcl-2 or Bcl-xL.
<b>CONCLUSION</b>: There is evidence to suggest that Bad expression levels at diagnosis influence time to biochemical relapse and overall survival, and that levels of pro-apoptotic proteins Bad and Bax fall during AIPC development. Bad might therefore represent a possible positive prognostic marker and potential therapeutic target for AIPC in the future
- âŠ