251 research outputs found
Triangular bases of integral closures
In this work, we consider the problem of computing triangular bases of
integral closures of one-dimensional local rings.
Let be a discrete valued field with valuation ring and
let be the maximal ideal. We take , a
monic irreducible polynomial of degree and consider the extension as well as the integral closure of
in , which we suppose to be finitely generated as an -module.
The algorithm , presented in this paper, computes
triangular bases of fractional ideals of . The theoretical
complexity is equivalent to current state of the art methods and in practice is
almost always faster. It is also considerably faster than the routines found in
standard computer algebra systems, excepting some cases involving very small
field extensions
Vector Positronium States in QED3
The homogeneous Bethe-Salpeter equation is solved in the quenched ladder
approximation for the vector positronium states of 4-component quantum
electrodynamics in 2 space and 1 time dimensions. Fermion propagator input is
from a Rainbow approximation Dyson-Schwinger solution, with a broad range of
fermion masses considered. This work is an extension of earlier work on the
scalar spectrum of the same model. The non-relativistic limit is also
considered via the large fermion mass limit. Classification of states via their
transformation properties under discrete parity transformations allows
analogies to be drawn with the meson spectrum of QCD.Comment: 24 pages, 2 encapsulated postscript figure
Self-consistent solution of the Schwinger-Dyson equations for the nucleon and meson propagators
The Schwinger-Dyson equations for the nucleon and meson propagators are
solved self-consistently in an approximation that goes beyond the Hartree-Fock
approximation. The traditional approach consists in solving the nucleon
Schwinger-Dyson equation with bare meson propagators and bare meson-nucleon
vertices; the corrections to the meson propagators are calculated using the
bare nucleon propagator and bare nucleon-meson vertices. It is known that such
an approximation scheme produces the appearance of ghost poles in the
propagators. In this paper the coupled system of Schwinger-Dyson equations for
the nucleon and the meson propagators are solved self-consistently including
vertex corrections. The interplay of self-consistency and vertex corrections on
the ghosts problem is investigated. It is found that the self-consistency does
not affect significantly the spectral properties of the propagators. In
particular, it does not affect the appearance of the ghost poles in the
propagators.Comment: REVTEX, 7 figures (available upon request), IFT-P.037/93,
DOE/ER/40427-12-N9
Automation and data processing with the immucor Galileo (R) system in a university blood bank
Background: The implementation of automated techniques improves the workflow and quality of immuno-hematological results. The workflows of our university blood bank were reviewed during the implementation of an automated immunohematological testing system. Methods: Work impact of blood grouping and subgrouping, cross- matching and antibody search using the Immucor Galileo system was compared to the previous used standard manual and semi- automated methods. Results: The redesign of our workflow did not achieve a significant reduction of the specimen's working process time, the operator's time however was reduced by 23%. Corresponding results were achieved for blood grouping, Rhesus typing, antibody screen and for autocontrol when changing from two semi- automated to the Galileo system. Because of the higher sensitivity of the Immucor antibody detection system, the rate of the initial positive antibody screens rose from 4 to 6% Conclusion: The Immucor Galileo system automates routine blood bank testing with high reliability, specificity and higher sensitivity compared to our previous used standard manual and semi- automated methods
The analytic structure of heavy quark propagators
The renormalised quark Dyson-Schwinger equation is studied in the limit of
the renormalised current heavy quark mass m_R --> infinity. We are particularly
interested in the analytic pole structure of the heavy quark propagator in the
complex momentum plane. Approximations in which the quark-gluon vertex is
modelled by either the bare vertex or the Ball-Chiu Ansatz, and the Landau
gauge gluon propagator takes either a gaussian form or a gaussian form with an
ultraviolet asymptotic tail are used.Comment: 21 pages Latex and 5 postscript figures. The original version of this
paper has been considerably extended to include a formalism dealing with the
renormalised heavy quark Dyson-Schwinger equation and uses a more realistic
Ansatz for the gluon propagator
Analytic Structure of the Quark Propagator in a Model with an infrared vanishing Gluon Propagator
The Dyson-Schwinger equation for the quark self energy is solved in rainbow
approximation using an infrared (IR) vanishing gluon propagator that introduces
an IR mass scale . There exists a dependent critical coupling indicating
the spontaneous breakdown of chiral symmetry. If one chooses realistic QCD
coupling constants the strength and the scale of spontaneous chiral symmetry
breaking decouple from the IR scale for small while for large no
dynamical chiral symmetry breaking occurs. At timelike momenta the quark
propagator possesses a pole, at least for a large range of the parameter .
Therefore it is suggestive that quarks are not confined in this model for all
values of . Furthermore, we argue that the quark propagator is analytic
within the whole complex momentum plane except on the timelike axis. Hence the
na\"{\i}ve Wick rotation is allowed.Comment: 19 pages, revtex, 7 figures, improved analysis of asymptotic
behaviour and slight changes in conclusion; to appear in Phys.Rev.
Dynamical chiral symmetry breaking and confinement with an infrared-vanishing gluon propagator?
We study a model Dyson-Schwinger equation for the quark propagator closed
using an {\it Ansatz} for the gluon propagator of the form \mbox{} and two {\it Ans\"{a}tze} for the quark-gluon vertex: the
minimal Ball-Chiu and the modified form suggested by Curtis and Pennington.
Using the quark condensate as an order parameter, we find that there is a
critical value of such that the model does not support dynamical chiral
symmetry breaking for . We discuss and apply a confinement test which
suggests that, for all values of , the quark propagator in the model {\bf is
not} confining. Together these results suggest that this Ansatz for the gluon
propagator is inadequate as a model since it does not yield the expected
behaviour of QCD.Comment: 21 Pages including 4 PostScript figures uuencoded at the end of the
file. Replacement: slight changes of wording and emphasis. ADP-93-215/T133,
ANL-PHY-7599-TH-93, FSU-SCRI-93-108, REVTEX 3.
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
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