91,496 research outputs found
Axial U(1) dynamics in eta and eta' photoproduction
We discuss the sensitivity of eta and eta' photoproduction near threshold to
the gluonic OZI breaking parameters in the U_A(1)-extended effective chiral
Lagrangian for low-energy QCD. Our coupled-channels analysis hints at a strong
correlation between the gluon-induced contributions to the eta' mass and the
low-energy pp -> pp eta' reaction and the near-threshold behaviour of the gamma
p -> eta p cross-section.Comment: 19 pages, 9 figure
Weightlifting competitions: lessons for performance management
Christos Genakos and Mario Pagliero look at professional weightlifters to assess the effects of reward systems based on relative performance.
Estimates for parameters and characteristics of the confining SU(3)-gluonic field in charged pions and kaons from leptonic decays and chiral symmetry breaking
The confinement mechanism proposed earlier by the author is employed for to
compute the decay constants corresponding to leptonic decays , , where stands for any meson from ,
. For this aim the weak axial form factor of -meson is
nonperturbatively calculated. The study entails estimates for parameters of the
confining SU(3)-gluonic field in charged pions and kaons. The corresponding
estimates of the gluon concentrations, electric and magnetic colour field
strengths are also adduced for the mentioned field at the scales of the mesons
under consideration. Further the obtained results are applied to the problem of
chiral symmetry breaking in quantum chromodynamics (QCD). It is shown that in
chirally symmetric world masses of pions and kaons are fully determined by the
confining SU(3)-gluonic field among (massless) , and quarks and not
equal to zero. Accordingly chiral symmetry is sufficiently rough approximate
one holding true only when neglecting the mentioned SU(3)-gluonic field between
quarks and no additional mechanism of the spontaneous chiral symmetry breaking
connected to the so-called Goldstone bosons is required. Finally, a possible
relation of the results obtained with a phenomenological string-like picture of
confinement is discussed too.Comment: 31 pages, LaTeX, 2 figures. Nucl. Phys. A812 (2008) to appea
The U(1) Problem in Chiral Random Matrix Models
We show that conventional asymmetric chiral random matrix models (ChRMM),
with a gaussian distribution in the asymmetry, provide for a screening of the
topological charge and a resolution of the problem in the unquenched
approximation. Our exact results to order are in agreement with numerical
estimates using large ensembles of asymmetric ChRMM with gaussian
distributions.Comment: ReVTaeX, 9 pages with 2 EPS figures. Uses the feynmf package version
1.0 for Feynman graph
Level crossing of particle-hole and mesonic modes in eta mesic nuclei
We study eta meson properties in the infinite nuclear matter and in atomic
nuclei with an emphasis on effects of the eta coupling to
N*(1535)--nucleon-hole modes. The N*(1535) resonance, which dominates the
low-energy eta-nucleon scattering, can be seen as a chiral partner of the
nucleon. The change of the chiral mass gap between the N* and the nucleon in a
nuclear medium has an impact on the properties of the eta-nucleus system. If
the N*-nucleon mass gap decreases with a density increase (chiral symmetry
restoration) the calculations show the existence of the resonance state at the
energy about 60 MeV and two bound eta-nucleus states with the binding energies
about -80 MeV. These states can have strong effect on predicted cross sections
of the ^12C (gamma,p) ^11B reaction with eta-meson production.Comment: 22 pages, 12 figure
Axial Vector Couplings of the Nucleon in Chiral Quark Model Incorporating Anomaly Effects
Renormalization of the axial vector currents due to Goldstone loops is
studied in a simple extension of Manohar - Georgi chiral quark model which
incorporates anomaly effects. The polarized strage quark sea in the
polarized nucleon results from different renormalization of the flavor singlet
and octet currents and is in reasonable agreement with the experiment.Comment: 11 pages REVtex, 2 figures sent upon reques
Fermion production despite fermion number conservation
Lattice proposals for a nonperturbative formulation of the Standard Model
easily lead to a global U(1) symmetry corresponding to exactly conserved
fermion number. The absence of an anomaly in the fermion current would then
appear to inhibit anomalous processes, such as electroweak baryogenesis in the
early universe. One way to circumvent this problem is to formulate the theory
such that this U(1) symmetry is explicitly broken. However we argue that in the
framework of spectral flow, fermion creation and annihilation still in fact
occurs, despite the exact fermion number conservation. The crucial observation
is that fermions are excitations relative to the vacuum, at the surface of the
Dirac sea. The exact global U(1) symmetry prohibits a state from changing its
fermion number during time evolution, however nothing prevents the fermionic
ground state from doing so. We illustrate our reasoning with a model in two
dimensions which has axial-vector couplings, first using a sharp momentum
cutoff, then using the lattice regulator with staggered fermions. The
difference in fermion number between the time evolved state and the ground
state is indeed in agreement with the anomaly. A study of the vacuum energy
shows that the perturbative counterterm needed for restoration of gauge
invariance is insufficient in a nonperturbative setting. For reference we also
study a closely related model with vector couplings, the Schwinger model, and
we examine the emergence of the -vacuum structure of both theories.Comment: 31 pages, LaTeX + uuencoded figs file (=5 PS figs). UvA-ITFA 94-17,
UCSD/PTH 94-0
Christos Tsiolkas's Style
This article takes up a specific feature of Christos Tsiolkas's writing, his style. Focusing on Tsiolkas's fourth novel, The Slap, this article argues that Tsiolkas’s style is an inarticulate style: a style that does not always use the right word at the right moment, that employs language for narrative utility rather than its own sake, and that sporadically departs from standard usage and correctness in ways that do not appear artistically motivated. My argument is that The Slap is notable among contemporary fiction in that what I consider to be Tsiolkas’s worst sentences are the most revealing of his inclinations as a novelist. Consequently, I depart from what has become a standard formula in Tsiolkas's reception, that where Tsiolkas succeeds as a writer he succeeds in spite of his style. Finally, this article also contributes to recent debates about the purpose and vocabulary of Australian literary discussion: how critics debate the work of a prize-winning author, how criticism and praise operate in critical judgements, and the significance of style in evaluations of literature
Neutral and Charged Polymers at Interfaces
Chain-like macromolecules (polymers) show characteristic adsorption
properties due to their flexibility and internal degrees of freedom, when
attracted to surfaces and interfaces. In this review we discuss concepts and
features that are relevant to the adsorption of neutral and charged polymers at
equilibrium, including the type of polymer/surface interaction, the solvent
quality, the characteristics of the surface, and the polymer structure. We pay
special attention to the case of charged polymers (polyelectrolytes) that have
a special importance due to their water solubility. We present a summary of
recent progress in this rapidly evolving field. Because many experimental
studies are performed with rather stiff biopolymers, we discuss in detail the
case of semi-flexible polymers in addition to flexible ones. We first review
the behavior of neutral and charged chains in solution. Then, the adsorption of
a single polymer chain is considered. Next, the adsorption and depletion
processes in the many-chain case are reviewed. Profiles, changes in the surface
tension and polymer surface excess are presented. Mean-field and corrections
due to fluctuations and lateral correlations are discussed. The force of
interaction between two adsorbed layers, which is important in understanding
colloidal stability, is characterized. The behavior of grafted polymers is also
reviewed, both for neutral and charged polymer brushes.Comment: a review: 130 pages, 30 ps figures; final form, added reference
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