2,533 research outputs found
WZW model based on the extended de Sitter group
We study the WZW model based on the centrally extended 2D de Sitter algebra.
We obtain the spacetime metric and its explicitly conformally flat expression.
The symmetries of the spacetime are found by identifying the Killing vectors
with the group generators. The energy-momentum tensor obtained from the
affine-Sugawara construction agrees with that from the more conventional
approach. The exact center charge agrees to one-loop order with the one-loop
beta function equations. We have also studied the representations of the
corresponding enveloping Virasoro algebra.Comment: 16 page
A Possible Mechanism for Pseudo-Gap in Cuprates
The electron spectrum in the normal phase of cuprates is analyzed in terms of
the boson-fermion model. It is argued that the existence of the uncondensed
pairs and the quasi-two-dimensional nature of the crystal structure are
responsible for the pseudo-gap above T_C observed recently.Comment: 19 pages, Plain Te
Color Superconductivity of QCD at High Baryon Density
At sufficiently high baryon density, a quark matter is expected to become a
color superconductor because of the pairing forces mediated by gluons. The
theoretical aspect of this novel phase of the strong interaction is reviewed
with the emphasis on the perturbation theory of QCD at high chemical potential
and low temperature. The derivation of the scaling formula of the
superconducting transition temperature at weak coupling is explained in detail.
The Ginzburg-Landau theory of the color superconductivity is also discussed.Comment: 52 pages, 10 figures, Lecture notes at CCAST domestic workshop
"Progresses in Color Superconductivity", Beijing, China, Dec.8-Dec.11, 200
Boson-Fermion Model of High-T_C Superconductivity ----A Progress Report
This is an invited lecture at the XXII International School of Theoretical
Physics, Ustron, Poland, 9/10-9/15, 1998. The boson-fermion model of high T_C
superconductivity is reviewed. Its applications to the pseudo-gap and DC
transport coefficients are discussed.Comment: 14 pages, 3 figures; A few changes in the quotation
The Meissner Effect in a Two Flavor LOFF Color Superconductor
We calculate the magnetic polarization tensor of the photon and of the gluons
in a two flavor color superconductor with a LOFF pairing that consists of a
single plane wave. We show that at zero temperature and within the range of the
values of the displacement of the Fermi sea that favors the LOFF state, all the
eigenvalues of the magnetic polarization tensor are positive. Therefore the
chromomagnetic instabilities pertaining to a gapless color superconductor
disappear.Comment: 20 pages and 7 figures, Latex, typos were corrected, references adde
A Novel Carrier Waveform Inter-Displacement Modulation Method in Underwater Communication Channel
As the main way of underwater wireless communication, underwater acoustic
communication is one of the focuses of ocean research. Compared with the free
space wireless communication channel, the underwater acoustic channel suffers
from more severe multipath effect, the less available bandwidth and the even
complex noise. The underwater acoustic channel is one of the most complicated
wireless communication channels. To achieve a reliable underwater acoustic
communication, Phase Shift Keying (PSK) modulation and Passive Time Reversal
Mirror (PTRM) equalization are considered to be a suitable scheme. However, due
to the serious distortion of the received signal caused by the channel, this
scheme suffers from a high Bit Error Rate (BER) under the condition of the low
Signal to Noise Ratio (SNR). To solve this problem, we proposes a Carrier
Waveform Inter-Displacement (CWID) modulation method based on the Linear
Frequency Modulation (LFM) PSK and PTRM scheme. The new communication scheme
reduces BER by increasing the difference from the carrier waveform for
different symbols. Simulation results show the effectiveness and superiority of
the proposed method.Comment: 8 pages, 11 figure
Chromomagnetic Instability and the LOFF state in a two flavor Color Superconductor
We explore the relation between the chromomagnetic instability of a
homogeneous two flavor color superconductor and the LOFF state. We perturb the
free energy of the 2SC by generating a small net momentum for the quark pair.
We find that the imaginary Meissner mass of a particular gluon implies that the
LOFF state is energetically favored.Comment: 11 pages, no figures, latex, discussion on charge neutrality, new
references were adde
On T-violation signals originating from magnetic orders through double exchange mechanism
The photon self energy tensor in a crystal with double exchange and
ferromagnetic or canting magnetic orders is analyzed at zero temperature with
emphasis on the signal of the time-reversal invariance breaking. Three
comparable contributions, spin susceptibility, local magnetic field and
spin-orbit coupling are estimated and the prospect of their experimental
detection is discussed.Comment: 21 page
Physical properties of the double exchange and its relevance to the specific heat of double perovskite materials
In response to the experimental discovery of double perovskite Ru- base
material, The magnetic and electronic properties of the double exchange
mechanism are studied theoretically. The electron band structure and the spin
wave spectrum response at zero temperature with the canting background are
computed from the first principle Hamiltonian. The long range Coulomb
interaction between charge carriers is found to be crucial in stabilizing the
canting order. A Monte Carlo simulation is performed on de-Gennes's effective
magnetic Hamiltonian with classical spin approximation. The peaks of the
specific heat as a function of temperature, which correspond to FM(AF) and
canting transitions, and its response to the external magnetic field are
consistent with the observation. For certain region of parameters, a more
complex canting order than layer type is found at sufficiently low temperature.
The effective interaction between carriers via exchanging a magnon wave is
found to be rather similar to that via exchanging an acoustic phonon. The pros
and cons to a genuine superconducting order in this system is analyzed.Comment: 42 page
A Possible Higher Order Correction to the chiral Vortical Conductivity in a Gauge Field Plasma
The two loop contributions to the chiral vortical conductivity are
considered. The Kubo formula together with the anomalous Ward identity of the
axial vector current suggest that there may be a nonzero correction to the
coefficient of the term of the conductivity.Comment: 6 pages, 2 figues, in latex, minor changes with typos fixed and a few
references adde
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