60,651 research outputs found
Star Products and Geometric Algebra
The formalism of geometric algebra can be described as deformed super
analysis. The deformation is done with a fermionic star product, that arises
from deformation quantization of pseudoclassical mechanics. If one then extends
the deformation to the bosonic coefficient part of superanalysis one obtains
quantum mechanics for systems with spin. This approach clarifies on the one
hand the relation between Grassmann and Clifford structures in geometric
algebra and on the other hand the relation between classical mechanics and
quantum mechanics. Moreover it gives a formalism that allows to handle
classical and quantum mechanics in a consistent manner.Comment: 21 page
Theory of Electric Transport in the Pseudogap State of High-Tc Cuprates
We theoretically investigate the electric transport in the pseudogap state of
High-Tc cuprates. Starting from the repulsive Hubbard model, we perform the
microscopic calculation to describe the pseudogap phenomena which are induced
by the superconducting fluctuations. The single particle Green function, spin
susceptibility and superconducting fluctuations are self-consistently
determined by the SC-FLEX+T-matrix approximation. The longitudinal and
transverse conductivities are calculated by using the Eliashberg and
Kohno-Yamada formalism. The effects of the spin fluctuations and
superconducting fluctuations are estimated, respectively. The vertex
corrections arising from the two fluctuations are also calculated. The
additional contribution from the Aslamazov-Larkin term is also estimated beyond
the Eliashberg formalism.
It is shown that the main effect of the superconducting fluctuations is the
feedback effect through the spin fluctuations. The correct results are obtained
by considering the superconducting fluctuations and the spin fluctuations
simultaneously. The temperature and doping dependences of the resistivity and
the Hall coefficient are well explained. We point out that the characteristic
momentum dependence of the systems plays an essential role in this explanation.Comment: To appear in J. Phys. Soc. Jpn. Vol.71 No.1 (2002
Cooper pairing above the critical temperature in a unitary Fermi gas
We present an ab initio determination of spin responses of the unitary Fermi
gas, based on finite temperature quantum Monte Carlo calculations and the Kubo
linear-response formalism. We determine the temperature dependence of the spin
susceptibility and the spin conductivity. We show that both quantities exhibit
suppression above the critical temperature of the superfluid to normal phase
transition due to presence of the Cooper pairs. The spin diffusion transport
coefficient does not display the existence of a minimum in the vicinity of the
critical temperature and it drops to very low values D_s approx 0.8hbar/m in
the superfluid phase. All these spin observables show a smooth and monotonic
behavior with temperature when crossing the critical temperature T_c, until the
Fermi liquid regime is attained at the temperature T*, where the pseudogap
regime disappears.Comment: 9 pages, 8 figures; supplemental materials included; published
versio
Keldysh approach to the renormalization group analysis of the disordered electron liquid
We present a Keldysh nonlinear sigma-model approach to the renormalization
group analysis of the disordered electron liquid. We include both the Coulomb
interaction and Fermi-liquid type interactions in the singlet and triplet
channels into the formalism. Based on this model, we reproduce the coupled
renormalization group equations for the diffusion coefficient, the frequency,
and interaction constants previously derived with the replica model in the
imaginary time technique. With the help of source fields coupling to the
particle-number and spin densities, we study the density-density and spin
density-spin density correlation functions in the diffusive regime. This allows
us to obtain results for the electric conductivity and the spin susceptibility
and thereby to re-derive the main results of the one-loop renormalization group
analysis of the disordered electron liquid in the Keldysh formalism.Comment: 29 pages, 15 figure
Equations of Motion of Spinning Relativistic Particle in Electromagnetic and Gravitational Fields
We consider the motion of a spinning relativistic particle in external
electromagnetic and gravitational fields, to first order in the external field,
but to an arbitrary order in spin. The noncovariant spin formalism is crucial
for the correct description of the influence of the spin on the particle
trajectory. We show that the true coordinate of a relativistic spinning
particle is its naive, common coordinate \r. Concrete calculations are
performed up to second order in spin included. A simple derivation is presented
for the gravitational spin-orbit and spin-spin interactions of a relativistic
particle. We discuss the gravimagnetic moment (GM), a specific spin effect in
general relativity. It is shown that for the Kerr black hole the gravimagnetic
ratio, i.e., the coefficient at the GM, equals unity (just as for the charged
Kerr hole the gyromagnetic ratio equals two). The equations of motion obtained
for relativistic spinning particle in external gravitational field differ
essentially from the Papapetrou equations.Comment: 32 pages, latex, Plenary talk at the Fairbank Meeting on the
Lense--Thirring Effect, Rome-Pescara, 29/6-4/7 199
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