179 research outputs found
Spectral change of sigma and omega mesons in a dense nuclear medium
The spectra of the scalar () and vector () mesons in nuclear
matter are studied in detail using the quark-meson coupling (QMC) model. It is
shown that above normal nuclear matter density the effects of -
mixing and the decay of the into change the spectra of
and mesons considerably. As in Quantum Hadrodynamics we find a
remarkable spectral change in the meson and the longitudinal mode of
the meson, namely a two-peak structure.Comment: 14 pages + 9 ps files for 4 figs. The paper was revised, and accepted
for publication in Physics Letters
Taming the Pion Cloud of the Nucleon
We present a light-front determination of the pionic contribution to the
nucleon self-energy, , to second-order in pion-baryon coupling
constants that allows the pion-nucleon vertex function to be treated in a
model-independent manner constrained by experiment. The pion mass
dependence of is consistent with chiral perturbation theory
results for small values of and is also linearly dependent on for
larger values, in accord with the results of lattice QCD calculations. The
derivative of with respect to yields the dominant
contribution to the pion content, which is consistent with the
difference observed experimentally in the violation of the
Gottfried sum rule.Comment: 11 pages, 3 figure
Meson-meson correlations in baryon-baryon and antibaryon-baryon interactions
Recent work of the J\"ulich group about the role of meson-meson correlations
in baryon-baryon and antibaryon-baryon interactions is reviewed.Comment: Lecture given at the Erice School 1995, TEX, 10 pages, 15 figure
Effect of Nucleon Structure Variation in Super-allowed Fermi Beta-decay
There is a well known anomaly between the value of the Fermi decay constant
extracted from super-allowed Fermi beta-decay of nuclear isotriplets and that
required by unitarity of the Cabibbo-Kobayashi-Maskawa matrix. This discrepancy
remains at the level of a few tenths of a percent after the most rigorous
investigation of conventional nuclear and radiative corrections. Within the
framework of the quark-meson coupling model of nuclear matter, which has been
previously applied successfully to phenomena such as nuclear saturation and
nuclear charge symmetry violation, we show that it is possible to understand a
significant fraction of the observed anomaly.Comment: 11 pages with 1 figure and 1 tabl
Progress in Understanding the Nuclear Equation of State at the Quark Level
At the present time there is a lively debate within the nuclear community
concerning the relevance of quark degrees of freedom in understanding nuclear
structure. We outline the key issues and review the impressive progress made
recently within the framework of the quark-meson coupling model. In particular,
we explain in quite general terms how the modification of the internal
structure of hadrons in-medium leads naturally to three- and four-body forces,
or equivalently, to density dependent effective interactions.Comment: Invited presentation at XXX Symposium on Nuclear Physics, Hacienda
Cocoyoc, Jan. 3-6, 200
The Nolen-Schiffer anomaly and isospin symmetry breaking in nuclear matter
The quark-meson coupling model which we have developed previously is extended
to incorporate the meson. It is then used to study the Nolen-Schiffer
anomaly and isospin symmetry breaking in nuclear matter. We find that, in
combination with the {\it u-d\/} mass difference, the difference between quark
scalar densities in protons and neutrons generates an effective neutron-proton
mass difference of the right magnitude. Finally we find that isospin symmetry
breaking in the quark condensates can be directly related to the meson
field.Comment: 13 page
Protein phosphatase 2A associates with and regulates atypical PKC and the epithelial tight junction complex
Tight junctions (TJs) play a crucial role in the establishment of cell polarity and regulation of paracellular permeability in epithelia. Here, we show that upon calcium-induced junction biogenesis in Madin-Darby canine kidney cells, ABαC, a major protein phosphatase (PP)2A holoenzyme, is recruited to the apical membrane where it interacts with the TJ complex. Enhanced PP2A activity induces dephosphorylation of the TJ proteins, ZO-1, occludin, and claudin-1, and is associated with increased paracellular permeability. Expression of PP2A catalytic subunit severely prevents TJ assembly. Conversely, inhibition of PP2A by okadaic acid promotes the phosphorylation and recruitment of ZO-1, occludin, and claudin-1 to the TJ during junctional biogenesis. PP2A negatively regulates TJ assembly without appreciably affecting the organization of F-actin and E-cadherin. Significantly, inhibition of atypical PKC (aPKC) blocks the calcium- and serum-independent membrane redistribution of TJ proteins induced by okadaic acid. Indeed, PP2A associates with and critically regulates the activity and distribution of aPKC during TJ formation. Thus, we provide the first evidence for calcium-dependent targeting of PP2A in epithelial cells, we identify PP2A as the first serine/threonine phosphatase associated with the multiprotein TJ complex, and we unveil a novel role for PP2A in the regulation of epithelial aPKC and TJ assembly and function
Quark-meson coupling model with the cloudy bag
Using the volume coupling version of the cloudy bag model, the quark-meson
coupling model is extended to study the role of pion field and the properties
of nuclear matter. The extended model includes the effect of gluon exchange as
well as the pion-cloud effect, and provides a good description of the nuclear
matter properties. The relationship between the extended model and the EFT
approach to nuclear matter is also discussed.Comment: 13 pages, 3 figure
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