45,461 research outputs found
Degeneracy of Ground State in Two-dimensional Electron-Lattice System
We discuss the ground state of a two dimensional electron-lattice system
described by a Su-Schrieffer-Heeger type Hamiltonian with a half-filled
electronic band, for which it has been pointed out in the previous paper [J.
Phys. Soc. Jpn. 69 (2000) 1769-1776] that the ground state distortion pattern
is not unique in spite of a unique electronic energy spectrum and the same
total energy. The necessary and sufficient conditions to be satisfied by the
distortion patterns in the ground state are derived numerically. As a result
the degrees of degeneracy in the ground state is estimated to be about
for with the linear dimension of the system.Comment: 2pages, 2figure
Polarization as a Probe to the Production Mechanisms of Charmonium in Collisions
Measurements of the polarization of \jp produced in pion-nucleus collisions
are in disagreement with leading twist QCD prediction where \jp is observed
to have negligible polarization whereas theory predicts substantial
polarization. We argue that this discrepancy cannot be due to poorly known
structure functions nor the relative production rates of \jp and .
The disagreement between theory and experiment suggests important higher twist
corrections, as has earlier been surmised from the anomalous non-factorized
nuclear -dependence of the \jp cross section.Comment: 8 page
SATMC: Spectral Energy Distribution Analysis Through Markov Chains
We present the general purpose spectral energy distribution (SED) fitting
tool SED Analysis Through Markov Chains (SATMC). Utilizing Monte Carlo Markov
Chain (MCMC) algorithms, SATMC fits an observed SED to SED templates or models
of the user's choice to infer intrinsic parameters, generate confidence levels
and produce the posterior parameter distribution. Here we describe the key
features of SATMC from the underlying MCMC engine to specific features for
handling SED fitting. We detail several test cases of SATMC, comparing results
obtained to traditional least-squares methods, which highlight its accuracy,
robustness and wide range of possible applications. We also present a sample of
submillimetre galaxies that have been fitted using the SED synthesis routine
GRASIL as input. In general, these SMGs are shown to occupy a large volume of
parameter space, particularly in regards to their star formation rates which
range from ~30-3000 M_sun yr^-1 and stellar masses which range from
~10^10-10^12 M_sun. Taking advantage of the Bayesian formalism inherent to
SATMC, we also show how the fitting results may change under different
parametrizations (i.e., different initial mass functions) and through
additional or improved photometry, the latter being crucial to the study of
high-redshift galaxies.Comment: 17 pages, 11 figures, MNRAS accepte
Zero-temperature criticality in the two-dimensional gauge glass model
The zero-temperature critical state of the two-dimensional gauge glass model
is investigated. It is found that low-energy vortex configurations afford a
simple description in terms of gapless, weakly interacting vortex-antivortex
pair excitations. A linear dielectric screening calculation is presented in a
renormalization group setting that yields a power-law decay of spin-wave
stiffness with distance. These properties are in agreement with low-temperature
specific heat and spin-glass susceptibility data obtained in large-scale
multi-canonical Monte Carlo simulations.Comment: 4 pages, 4 figure
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