11,184 research outputs found
Contribution of Continuum in the QCD Sum Rule for
Using the soft-pion theorem and the assumption on the final-state
interactions, we include the contribution of continuum into the QCD sum
rules for meson. We find that this contribution can
significantly lower the mass and the decay constant of state. For
the value of the current quark mass , we obtain the
mass of in the interval , being in agreement with the experimental data, and the vector
current decay constant of , much
lower than those obtained in previous literature
Physical decomposition of the gauge and gravitational fields
Physical decomposition of the non-Abelian gauge field has recently solved the
two-decade-lasting problem of a meaningful gluon spin. Here we extend this
approach to gravity and attack the century-lasting problem of a meaningful
gravitational energy. The metric is unambiguously separated into a pure
geometric term which contributes null curvature tensor, and a physical term
which represents the true gravitational effect and always vanishes in a flat
space-time. By this decomposition the conventional pseudo-tensors of the
gravitational stress-energy are easily rescued to produce definite physical
result. Our decomposition applies to any symmetric tensor, and has interesting
relation to the transverse-traceless (TT) decomposition discussed by Arnowitt,
Deser and Misner, and by York.Comment: 11 pages, no figure; significant revision, with discussion on
relations of various metric decomposition
On the Cosmic Evolution of Fe/Mg in QSO Absorption Line Systems
We investigate the variation of the ratio of the equivalent widths of the
FeII2600 line to the MgII2796,2803 doublet as a
function of redshift in a large sample of absorption lines drawn from the
JHU-SDSS Absorption Line Catalog. We find that despite large scatter, the
observed ratio shows a trend where the equivalent width ratio
decreases monotonically with
increasing redshift over the range . Selecting the
subset of absorbers where the signal-to-noise ratio of the MgII equivalent
width is 3 and modeling the equivalent width ratio
distribution as a gaussian, we find that the mean of the gaussian distribution
varies as . We discuss various possible
reasons for the trend. A monotonic trend in the Fe/Mg abundance ratio is
predicted by a simple model where the abundances of Mg and Fe in the absorbing
clouds are assumed to be the result of supernova ejecta and where the cosmic
evolution in the SNIa and core-collapse supernova rates is related to the
cosmic star-formation rate. If the trend in reflects the
evolution in the abundances, then it is consistent with the predictions of the
simple model.Comment: 10 pages, 4 figures, final version published in MNRA
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