4,256 research outputs found
Facets of confinement and dynamical chiral symmetry breaking
The gap equation is a cornerstone in understanding dynamical chiral symmetry
breaking and may also provide clues to confinement. A symmetry-preserving
truncation of its kernel enables proofs of important results and the
development of an efficacious phenomenology. We describe a model of the kernel
that yields: a momentum-dependent dressed-quark propagator in fair agreement
with quenched lattice-QCD results; and chiral limit values: f_pi= 68 MeV and
= -(190 MeV)^3. It is compared with models inferred from studies of
the gauge sector.Comment: 5 pages, 3 figures; contribution to the proceedings of Quark Nuclear
Physics (QNP 2002), Juelich, Germany, 9-14 Jun 200
Logic system aids in evaluation of project readiness
Measurement Operational Readiness Requirements /MORR/ assignments logic is used for determining the readiness of a complex project to go forward as planned. The system used logic network which assigns qualities to all important criteria in a project and establishes a logical sequence of measurements to determine what the conditions are
Mind the gap
In this summary of the application of Dyson-Schwinger equations to the theory
and phenomenology of hadrons, some deductions following from a nonperturbative,
symmetry-preserving truncation are highlighted, notable amongst which are
results for pseudoscalar mesons. We also describe inferences from the gap
equation relating to the radius of convergence of a chiral expansion,
applications to heavy-light and heavy-heavy mesons, and quantitative estimates
of the contribution of quark orbital angular momentum in pseudoscalar mesons;
and recapitulate upon studies of nucleon electromagnetic form factors.Comment: 7 pages, 3 figures. Contribution to Proceedings of 4th International
Conference on Quarks and Nuclear Physics (QNP06), Madrid, Spain, 5-10 Jun
200
Evaluating Rice Straw as a Substitute for Barley Straw in Inhibiting Algal Growth in Farm Ponds
Algal blooms disrupt aquatic ecosystems and are more common in lakes, ponds, and rivers during the summer months due to nutrient pollution. Livestock production can contribute increased quantities of nutrients to water bodies from runoff of manure. Commonly used mechanical and chemical control methods may have limited success because algae are small and propagate quickly. Barley (Hordeum vulgare) straw has been shown to inhibit the growth of algae as the straw decomposes aerobically in ponds. Therefore, barley represents a natural option for algal biomass control. However, the small amount of barley production in Arkansas limits the availability of barley straw as a solution to control algal blooms locally. Other cereal grain straws may produce similar inhibitory effects during decomposition. Rice (Oryza sativa) is produced in large quantities in Arkansas, making rice straw a locally sourced straw product. The objective of this research was to determine the efficacy of using rice compared to barley straw to inhibit algal growth in freshwater ponds. Data were collected from nine farm ponds, three treated with rice straw, three treated with barley straw, and three without amendment to serve as the experimental control. Dissolved oxygen, pH, nitrate-nitrogen (NO3--N), dissolved phosphorus (P), temperature, and turbidity were measured for 14 weeks from June 12 to September 17, 2018. Algal biomass was measured as chlorophyll-a concentration to evaluate treatment effectiveness over time. Dissolved oxygen was significantly influenced by treatment and time. The NO3--N concentration in ponds treated with rice straw was significantly greater than the control and barley treatment. Chlorophyll-a concentrations were variable, and there were no consistent trends through time within a treatment. More research under controlled conditions to understand impacts of abiotic conditions, microbial and algal community compositions, and mode of action of algal inhibition is required before cereal straw can be a reliable, locally sourced method of algal control in farm ponds
Leading-order calculation of hadronic contributions to the muon using the Dyson-Schwinger approach
We present a calculation of the hadronic vacuum polarization (HVP) tensor
within the framework of Dyson--Schwinger equations. To this end we use a
well-established phenomenological model for the quark-gluon interaction with
parameters fixed to reproduce hadronic observables. From the HVP tensor we
compute both the Adler function and the HVP contribution to the anomalous
magnetic moment of the muon, . We find which deviates about two percent from the value extracted from
experiment. Additionally, we make comparison with a recent lattice
determination of and find good agreement within our approach. We
also discuss the implications of our result for a corresponding calculation of
the hadronic light-by-light scattering contribution to .Comment: 9 pages, 8 figure
Confinement Phenomenology in the Bethe-Salpeter Equation
We consider the solution of the Bethe-Salpeter equation in Euclidean metric
for a qbar-q vector meson in the circumstance where the dressed quark
propagators have time-like complex conjugate mass poles. This approximates
features encountered in recent QCD modeling via the Dyson-Schwinger equations;
the absence of real mass poles simulates quark confinement. The analytic
continuation in the total momentum necessary to reach the mass shell for a
meson sufficiently heavier than 1 GeV leads to the quark poles being within the
integration domain for two variables in the standard approach. Through Feynman
integral techniques, we show how the analytic continuation can be implemented
in a way suitable for a practical numerical solution. We show that the would-be
qbar-q width to the meson generated from one quark pole is exactly cancelled by
the effect of the conjugate partner pole; the meson mass remains real and there
is no spurious qbar-q production threshold. The ladder kernel we employ is
consistent with one-loop perturbative QCD and has a two-parameter infrared
structure found to be successful in recent studies of the light SU(3) meson
sector.Comment: Submitted for publication; 10.5x2-column pages, REVTEX 4, 3
postscript files making 3 fig
Strong Decays of Light Vector Mesons
The vector meson strong decays rho-->pi pi, phi-->KK, and K^star-->pi K are
studied within a covariant approach based on the ladder-rainbow truncation of
the QCD Dyson--Schwinger equation for the quark propagator and the
Bethe--Salpeter equation for the mesons. The model preserves the one-loop
behavior of QCD in the ultraviolet, has two infrared parameters, and implements
quark confinement and dynamical chiral symmetry breaking. The 3-point decay
amplitudes are described in impulse approximation. The Bethe--Salpeter study
motivates a method for estimating the masses for heavier mesons within this
model without continuing the propagators into the complex plane. We test the
accuracy via the rho, phi and K^{star} masses and then produce estimates of the
model results for the a_1 and b_1 masses as well as the mass of the proposed
exotic vector pi_1(1400).Comment: Submitted for publication; 10x2-column pages, REVTEX 4, 3 .eps files
making 3fig
Vector meson form factors and their quark-mass dependence
The electromagnetic form factors of vector mesons are calculated in an
explicitly Poincar\'e covariant formulation, based on the Dyson--Schwinger
equations of QCD, that respects electromagnetic current conservation, and
unambiguously incorporates effects from vector meson poles in the quark-photon
vertex. This method incorporates a 2-parameter effective interaction, where the
parameters are constrained by the experimental values of chiral condensate and
. This approach has successfully described a large amount of
light-quark meson experimental data, e.g. ground state pseudoscalar masses and
their electromagnetic form factors; ground state vector meson masses and strong
and electroweak decays. Here we apply it to predict the electromagnetic
properties of vector mesons. The results for the static properties of the
-meson are: charge radius , magnetic
moment , and quadrupole moment . We investigate
the quark mass dependence of these static properties and find that our results
at the charm quark mass are in agreement with recent lattice simulations. The
charge radius decreases with increasing quark mass, but the magnetic moment is
almost independent of the quark mass.Comment: 13 pages, 7 figure
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