640 research outputs found
Anomalous tag diffusion in the asymmetric exclusion model with particles of arbitrary sizes
Anomalous behavior of correlation functions of tagged particles are studied
in generalizations of the one dimensional asymmetric exclusion problem. In
these generalized models the range of the hard-core interactions are changed
and the restriction of relative ordering of the particles is partially brocken.
The models probing these effects are those of biased diffusion of particles
having size S=0,1,2,..., or an effective negative "size" S=-1,-2,..., in units
of lattice space. Our numerical simulations show that irrespective of the range
of the hard-core potential, as long some relative ordering of particles are
kept, we find suitable sliding-tag correlation functions whose fluctuations
growth with time anomalously slow (), when compared with the normal
diffusive behavior (). These results indicate that the critical
behavior of these stochastic models are in the Kardar-Parisi-Zhang (KPZ)
universality class. Moreover a previous Bethe-ansatz calculation of the
dynamical critical exponent , for size particles is extended to
the case and the KPZ result is predicted for all values of .Comment: 4 pages, 3 figure
Low energy and dynamical properties of a single hole in the t-Jz model
We review in details a recently proposed technique to extract information
about dynamical correlation functions of many-body hamiltonians with a few
Lanczos iterations and without the limitation of finite size. We apply this
technique to understand the low energy properties and the dynamical spectral
weight of a simple model describing the motion of a single hole in a quantum
antiferromagnet: the model in two spatial dimension and for a double
chain lattice. The simplicity of the model allows us a well controlled
numerical solution, especially for the two chain case. Contrary to previous
approximations we have found that the single hole ground state in the infinite
system is continuously connected with the Nagaoka fully polarized state for
. Analogously we have obtained an accurate determination of the
dynamical spectral weight relevant for photoemission experiments. For
an argument is given that the spectral weight vanishes at the Nagaoka energy
faster than any power law, as supported also by a clear numerical evidence. It
is also shown that spin charge decoupling is an exact property for a single
hole in the Bethe lattice but does not apply to the more realistic lattices
where the hole can describe closed loop paths.Comment: RevTex 3.0, 40 pages + 16 Figures in one file self-extracting, to
appear in Phys. Rev
The Dimensional-Reduction Anomaly in Spherically Symmetric Spacetimes
In D-dimensional spacetimes which can be foliated by n-dimensional
homogeneous subspaces, a quantum field can be decomposed in terms of modes on
the subspaces, reducing the system to a collection of (D-n)-dimensional fields.
This allows one to write bare D-dimensional field quantities like the Green
function and the effective action as sums of their (D-n)-dimensional
counterparts in the dimensionally reduced theory. It has been shown, however,
that renormalization breaks this relationship between the original and
dimensionally reduced theories, an effect called the dimensional-reduction
anomaly. We examine the dimensional-reduction anomaly for the important case of
spherically symmetric spaces.Comment: LaTeX, 19 pages, 2 figures. v2: calculations simplified, references
adde
Numerical renormalization group study of the 1D t-J model
The one-dimensional (1D) model is investigated using the density matrix
renormalization group (DMRG) method. We report for the first time a
generalization of the DMRG method to the case of arbitrary band filling and
prove a theorem with respect to the reduced density matrix that accelerates the
numerical computation. Lastly, using the extended DMRG method, we present the
ground state electron momentum distribution, spin and charge correlation
functions. The anomaly of the momentum distribution function first
discussed by Ogata and Shiba is shown to disappear as increases. We also
argue that there exists a density-independent beyond which the system
becomes an electron solid.Comment: Wrong set of figures were put in the orginal submissio
Noise Kernel and Stress Energy Bi-Tensor of Quantum Fields in Hot Flat Space and Gaussian Approximation in the Optical Schwarzschild Metric
Continuing our investigation of the regularization of the noise kernel in
curved spacetimes [N. G. Phillips and B. L. Hu, Phys. Rev. D {\bf 63}, 104001
(2001)] we adopt the modified point separation scheme for the class of optical
spacetimes using the Gaussian approximation for the Green functions a la
Bekenstein-Parker-Page. In the first example we derive the regularized noise
kernel for a thermal field in flat space. It is useful for black hole
nucleation considerations. In the second example of an optical Schwarzschild
spacetime we obtain a finite expression for the noise kernel at the horizon and
recover the hot flat space result at infinity. Knowledge of the noise kernel is
essential for studying issues related to black hole horizon fluctuations and
Hawking radiation backreaction. We show that the Gaussian approximated Green
function which works surprisingly well for the stress tensor at the
Schwarzschild horizon produces significant error in the noise kernel there. We
identify the failure as occurring at the fourth covariant derivative order.Comment: 21 pages, RevTeX
Dispersion of a single hole in the t-J model
The dispersion of a single hole in the t-J model obtained by the exact result
of 32 sites and the results obtained by self-consistent Born approximation and
the Green function Monte Carlo method can be simply derived by a mean-field
theory with d-RVB and antiferromagnetic order parameters. In addition, it
offers a simple explanation for the difference observed between those results.
The presence of the extended van Hove region at (pi,0) is a consequence of the
d-RVB pairing independenct of the antiferromagnetic order. Results including t'
and t" are also presented and explained consistently in a similar way.Comment: LaTex file, 5 pages with 5 embedded eps figure
Hubbard model versus t-J model: The one-particle spectrum
The origin of the apparent discrepancies between the one-particle spectra of
the Hubbard and t-J models is revealed: Wavefunction corrections, in addition
to the three-site terms, should supplement the bare t-J. In this way a
quantitative agreement between the two models is obtained, even for the
intermediate- values appropriate for the high-Tc cuprate superconductors.
Numerical results for clusters of up to 20 sites are presented. The momentum
dependence of the observed intensities in the photoemission spectra of
Sr2CuO2Cl2 are well described by this complete strong-coupling approach.Comment: 4 two-column RevTeX pages, including 4 Postscript figures. Uses epsf.
Accepted for publication in Physical Review B, Rapid Communicatio
- âŠ