1,708 research outputs found
Quark zero modes in intersecting center vortex gauge fields
The zero modes of the Dirac operator in the background of center vortex gauge
field configurations in and are examined. If the net flux in D=2
is larger than 1 we obtain normalizable zero modes which are mainly localized
at the vortices. In D=4 quasi-normalizable zero modes exist for intersecting
flat vortex sheets with the Pontryagin index equal to 2. These zero modes are
mainly localized at the vortex intersection points, which carry a topological
charge of . To circumvent the problem of normalizability the
space-time manifold is chosen to be the (compact) torus \T^2 and \T^4,
respectively. According to the index theorem there are normalizable zero modes
on \T^2 if the net flux is non-zero. These zero modes are localized at the
vortices. On \T^4 zero modes exist for a non-vanishing Pontryagin index. As
in these zero modes are localized at the vortex intersection points.Comment: 20 pages, 4 figures, LaTeX2e, references added, treatment of ideal
vortices on the torus shortene
Heavy Quark Solitons in the Nambu--Jona-Lasinio Model
The Nambu--Jona-Lasinio model (NJL) is extended to incorporate heavy quark
spin-symmetry. In this model baryons containing one heavy quark are analyzed as
bound-states of light baryons, represented as chiral solitons, and mesons
containing one heavy quark. From related studies in Skyrme type models, the
ground-state heavy baryon is known to arise for the heavy meson in a P--wave
configuration. In the limit of an infinitely large quark mass the heavy meson
wave-function is sharply peaked at the center of the chiral soliton. Therefore
the bound state equation reduces to an eigenvalue problem for the coefficients
of the operators contained in the most general P-wave {\it ansatz} for the
heavy meson. Within the NJL model a novel feature arises from the coupling of
the heavy meson to the various light quark states. In this respect conceptual
differences to Skyrme model calculations are discovered: The strongest bound
state is given by a heavy meson configuration which is completely decoupled
from the grand spin zero channel of the light quarks.Comment: 16 pages REVTEX, one postscript figure, to appear in Phys. Rev.
Pesquisa com banana no Brasil: uma análise retrospectiva com visão de futuro.
A bananicultura brasileira tem se mantido estável em relação à área plantada, mas a partir dos anos 80 cresceu cerca de 130% em sua produtividade, em resposta à incorporação de tecnologias desenvolvidas ou adaptadas pela pesquisa. Uma análise crítica dos resultados obtidos pela pesquisa será realizada e caminhos que possam trazer maiores avanços serão sugeridos
Production Processes as a Tool to Study Parameterizations of Quark Confinement
We introduce diquarks as separable correlations in the two-quark Green's
function to facilitate the description of baryons as relativistic three-quark
bound states. These states then emerge as solutions of Bethe-Salpeter equations
for quarks and diquarks that interact via quark exchange. When solving these
equations we consider various dressing functions for the free quark and diquark
propagators that prohibit the existence of corresponding asymptotic states and
thus effectively parameterize confinement. We study the implications of
qualitatively different dressing functions on the model predictions for the
masses of the octet baryons as well as the electromagnetic and strong form
factors of the nucleon. For different dressing functions we in particular
compare the predictions for kaon photoproduction, , and
associated strangeness production, with experimental data.
This leads to conclusions on the permissibility of different dressing
functions.Comment: 43 pages, Latex, 28 eps files included via epsfig; version to be
published in Physical Review
A method for collective excitation of Bose-Einstein condensate
It is shown that by an appropriate modification of the trapping potential one
may create collective excitation in cold atom Bose-Einstein condensate. The
proposed method is complementary to earlier suggestions. It seems to be
feasible experimentally --- it requires only a proper change in time of the
potential in atomic traps, as realized in laboratories already.Comment: 4 pages, 4 figures; major revision, several references added,
interacting particles case adde
Impacts of both reference population size and inclusion of a residual polygenic effect on the accuracy of genomic prediction
<p>Abstract</p> <p>Background</p> <p>The purpose of this work was to study the impact of both the size of genomic reference populations and the inclusion of a residual polygenic effect on dairy cattle genetic evaluations enhanced with genomic information.</p> <p>Methods</p> <p>Direct genomic values were estimated for German Holstein cattle with a genomic BLUP model including a residual polygenic effect. A total of 17,429 genotyped Holstein bulls were evaluated using the phenotypes of 44 traits. The Interbull genomic validation test was implemented to investigate how the inclusion of a residual polygenic effect impacted genomic estimated breeding values.</p> <p>Results</p> <p>As the number of reference bulls increased, both the variance of the estimates of single nucleotide polymorphism effects and the reliability of the direct genomic values of selection candidates increased. Fitting a residual polygenic effect in the model resulted in less biased genome-enhanced breeding values and decreased the correlation between direct genomic values and estimated breeding values of sires in the reference population.</p> <p>Conclusions</p> <p>Genetic evaluation of dairy cattle enhanced with genomic information is highly effective in increasing reliability, as well as using large genomic reference populations. We found that fitting a residual polygenic effect reduced the bias in genome-enhanced breeding values, decreased the correlation between direct genomic values and sire's estimated breeding values and made genome-enhanced breeding values more consistent in mean and variance as is the case for pedigree-based estimated breeding values.</p
Yang-Mills Theory In Axial Gauge
The Yang-Mills functional integral is studied in an axial variant of 't
Hooft's maximal Abelian gauge. In this gauge Gau\ss ' law can be completely
resolved resulting in a description in terms of unconstrained variables.
Compared to previous work along this line starting with work of Goldstone and
Jackiw one ends up here with half as many integration variables, besides a
field living in the Cartan subgroup of the gauge group and in D-1 dimension.
The latter is of particular relevance for the infrared behaviour of the theory.
Keeping only this variable we calculate the Wilson loop and find an area law.Comment: 43 pages REVTeX, 6 figure
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