845 research outputs found
Moments of Structure Functions in Full QCD
Moments of the quark density distribution, moments of the quark helicity
distribution, and the tensor charge are calculated in full QCD. Calculations of
matrix elements of operators from the operator product expansion have been
performed on lattices for Wilson fermions at
using configurations from the SESAM collaboration and at using
configurations from SCRI. One-loop perturbative renormalization corrections are
included. Selected results are compared with corresponding quenched
calculations and with calculations using cooled configurations.Comment: Lattice 2000 (Hadronic Matrix Elements), 4 pages, 5 figure
B_K from quenched overlap QCD
We present an exploratory calculation of the standard model Delta S=2 matrix
element relevant for indirect CP violation in K -> pi pi decays. The
computation is performed with overlap fermions in the quenched approximation at
beta=6.0 on a 16^3x32 lattice. The resulting bare matrix element is
renormalized non-perturbatively. Our preliminary result is B_K^{NDR}(2
GeV)=0.61(7), where the error does not yet include an estimate of systematic
uncertainties.Comment: 3 pages, 2 figures, Lattice2002(matrixel). Parallel session talk by
L. Lellouch at the 20th International Symposium on Lattice Field Theory
(Lattice 2002), Boston, Massachusetts, 24-29 June 200
Recent advances in analytical approaches for the standardization and quality of polyphenols of propolis
Analytical approaches utilized for the characterization of polyphenols from propolis useful for the
determination of its quality is investigated in this study. A qualitative and quantitative evaluation of
propolis bioactive molecules is of interest in medicine and nutraceuticals. Recent powerful analytical
techniques are of great utility to separate and quantify polyphenols in extracts and finished products
due to their capacity to produce typical fingerprints and a reliable identification of many components.
According to this, an HPLC-UV-MS procedure was validated and applied for the characterization and
quantification of bioactive substances in propolis and for an accurate assessment of their content in
extract samples. By using this analytical approach, we obtained specific compositions related to brown
propolis acquired from different geographic areas (and preparations and treatment). This is more
important by considering the scientific opinion of European Food Safety Authority (EFSA) which
provided a negative response related to health claims of propolis and its polyphenols. These results
prove that HPLC-MS is an attractive tool for the standardization and quality control of propolis and may
be realistically applied to screen raw material and to evaluate finished commercial preparations and
nutraceutical benefits
On the discretization of physical momenta in lattice QCD
The adoption of two distinct boundary conditions for two fermions species on
a finite lattice allows to deal with arbitrary relative momentum between the
two particle species, in spite of the momentum quantization rule due to a
limited physical box size. We test the physical significance of this
topological momentum by checking in the continuum limit the validity of the
expected energy-momentum dispersion relations.Comment: 9 pages, 3 figures; references added; no changes in text or results;
version accepted for pubblication in Phys. Lett.
Numerical Exploration of the RI/MOM Scheme Gauge Dependence
The gauge dependence of some fermion bilinear RI/MOM renormalization
constants is studied by comparing data which have been gauge-fixed in two
different realizations of the Landau gauge and in a generic covariant gauge.
The very good agreement between the various sets of results and the theory
indicates that the numerical uncertainty induced by the lattice gauge-fixing
procedure is below the statistical errors of our data sample which is of the
order of (1-1.5)%.Comment: 3 pages, 2 figures, Lattice2002(theoretical
Moments of Nucleon Light Cone Quark Distributions Calculated in Full Lattice QCD
Moments of the quark density, helicity, and transversity distributions are
calculated in unquenched lattice QCD. Calculations of proton matrix elements of
operators corresponding to these moments through the operator product expansion
have been performed on lattices for Wilson fermions at using configurations from the SESAM collaboration and at
using configurations from SCRI. One-loop perturbative renormalization
corrections are included. At quark masses accessible in present calculations,
there is no statistically significant difference between quenched and full QCD
results, indicating that the contributions of quark-antiquark excitations from
the Dirac Sea are small. Close agreement between calculations with cooled
configurations containing essentially only instantons and the full gluon
configurations indicates that quark zero modes associated with instantons play
a dominant role. Naive linear extrapolation of the full QCD calculation to the
physical pion mass yields results inconsistent with experiment. Extrapolation
to the chiral limit including the physics of the pion cloud can resolve this
discrepancy and the requirements for a definitive chiral extrapolation are
described.Comment: 53 Pages Revtex, 26 Figures, 9 Tables. Added additional reference and
updated referenced data in Table I
Factors influencing the first thousand days of life
The first 1,000 days is a vulnerable phase in which parents, institutions and health professionals should create early interventions for the proper development and promotion of good health
One loop matching coefficients for a variant overlap action--and some of its simpler relatives
I present one-loop perturbative calculations of matching coefficients between
matrix elements in continuum regulated QCD and lattice QCD with overlap
fermions, with emphasis a recently-proposed variant discretization of the
overlap. These fermions have extended (``fat link'') gauge connections. The
scale for evaluation of the running coupling constant (in the context of the
Lepage-Mackenzie fixing scheme) is also given.
A variety of results (for additive mass renormalization, local currents, and
some non-penguin four-fermion operators) for naive, Wilson, clover, and overlap
actions are shown.Comment: 17 pages, Revtex, 11 postscript figures. COLO-HEP-48
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