15,352 research outputs found
Atomic Ground-State Energies
It is demonstrated that atomic Hartree–Fock binding energies may be reproduced with great accuracy (within about four parts in a thousand) by a scaled model system in which the electrons are noninteracting, and are bound in a bare Coulomb potential. </jats:p
An Approximate Light Cone Method to Investigate Meson Structure
To appear in the proceedings of The Phenomenology of Large N(c) QCD, Tempe,
Arizona, 9-11 Jan 2002.Comment: 5 pages, 2 figures, other comment
On Subleading Contributions to the AdS/CFT Trace Anomaly
In the context of the AdS/CFT correspondence, we perform a direct computation
in AdS_5 supergravity of the trace anomaly of a d=4, N=2 SCFT. We find
agreement with the field theory result up to next to leading order in the 1/N
expansion. In particular, the order N gravitational contribution to the anomaly
is obtained from a Riemann tensor squared term in the 7-brane effective action
deduced from heterotic - type I duality. We also discuss, in the AdS/CFT
context, the order N corrections to the trace anomaly in d=4, N=4 SCFTs
involving SO or Sp gauge groups.Comment: 25 pages, LaTeX, v2: references adde
Complex Matrix Models and Statistics of Branched Coverings of 2D Surfaces
We present a complex matrix gauge model defined on an arbitrary
two-dimensional orientable lattice. We rewrite the model's partition function
in terms of a sum over representations of the group U(N). The model solves the
general combinatorial problem of counting branched covers of orientable Riemann
surfaces with any given, fixed branch point structure. We then define an
appropriate continuum limit allowing the branch points to freely float over the
surface. The simplest such limit reproduces two-dimensional chiral U(N)
Yang-Mills theory and its string description due to Gross and Taylor.Comment: 21 pages, 2 figures, TeX, harvmac.tex, epsf.tex, TeX "big
Symmetrized importance samplers for stochastic differential equations
We study a class of importance sampling methods for stochastic differential
equations (SDEs). A small-noise analysis is performed, and the results suggest
that a simple symmetrization procedure can significantly improve the
performance of our importance sampling schemes when the noise is not too large.
We demonstrate that this is indeed the case for a number of linear and
nonlinear examples. Potential applications, e.g., data assimilation, are
discussed.Comment: Added brief discussion of Hamilton-Jacobi equation. Also made various
minor corrections. To appear in Communciations in Applied Mathematics and
Computational Scienc
Small-noise analysis and symmetrization of implicit Monte Carlo samplers
Implicit samplers are algorithms for producing independent, weighted samples
from multi-variate probability distributions. These are often applied in
Bayesian data assimilation algorithms. We use Laplace asymptotic expansions to
analyze two implicit samplers in the small noise regime. Our analysis suggests
a symmetrization of the algo- rithms that leads to improved (implicit) sampling
schemes at a rel- atively small additional cost. Computational experiments
confirm the theory and show that symmetrization is effective for small noise
sampling problems
Spin excitations in fluctuating stripe phases of doped cuprate superconductors
Using a phenomenological lattice model of coupled spin and charge modes, we
determine the spin susceptibility in the presence of fluctuating stripe charge
order. We assume the charge fluctuations to be slow compared to those of the
spins, and combine Monte Carlo simulations for the charge order parameter with
exact diagonalization of the spin sector. Our calculations unify the spin
dynamics of both static and fluctuating stripe phases and support the notion of
a universal spin excitation spectrum in doped cuprate superconductors.Comment: 4 pages, 4 figs, minor changes, final version as publishe
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