156 research outputs found
A mechanism for the Double-Spin Asymmetry in Electromagnetic Production at HERMES
We calculate the contribution of meson and pomeron exchanges to the
double-spin asymmetry in -meson electromagnetic production at HERMES
energies. We show that the observed double-spin asymmetries, which are large,
can be explained by the interference between the natural parity -secondary
Reggeon and the unnatural parity anomalous exchanges.Comment: 7 pages, 3 figures, Late
"Free" Constituent Quarks and Dilepton Production in Heavy Ion Collisions
An approach is suggested, invoking vitally the notion of constituent massive
quarks (valons) which can survive and propagate rather than hadrons (except of
pions) within the hot and dense matter formed below the chiral transition
temperature in course of the heavy ion collisions at high energies. This
approach is shown to be quite good for description of the experimentally
observed excess in dilepton yield at masses 250 MeV < M < 700 MeV over the
prompt resonance decay mechanism (CERES cocktail) predictions. In certain
aspects, it looks to be even more successful, than the conventional approaches:
it seems to match the data somewhat better at dilepton masses before the
two-pion threshold and before the rho-meson peak as well as at higher dilepton
masses (beyond the phi-meson one). The approach implies no specific assumptions
on the equation of state (EOS) or peculiarities of phase transitions in the
expanding nuclear matter.Comment: 13 pages, 3 PNG figures. submitted to Sov. Nucl. Phy
QCD sum rule analysis for light vector and axial-vector mesons in vacuum and nuclear matter
Extending previous work we study the constraints of QCD sum rules on mass and
width of light vector and axial-vector mesons in vacuum and in a medium with
finite nuclear density. For the latter case especially the effect of nuclear
pions leading to vector-axial-vector mixing is included in the analysis.Comment: RevTeX, 32 pages, 10 eps figure
Spin-Isospin Structure and Pion Condensation in Nucleon Matter
We report variational calculations of symmetric nuclear matter and pure
neutron matter, using the new Argonne v18 two-nucleon and Urbana IX
three-nucleon interactions. At the equilibrium density of 0.16 fm^-3 the
two-nucleon densities in symmetric nuclear matter are found to exhibit a
short-range spin-isospin structure similar to that found in light nuclei. We
also find that both symmetric nuclear matter and pure neutron matter undergo
transitions to phases with pion condensation at densities of 0.32 fm^-3 and 0.2
fm^-3, respectively. Neither transtion occurs with the Urbana v14 two-nucleon
interaction, while only the transition in neutron matter occurs with the
Argonne v14 two-nucleon interaction. The three-nucleon interaction is required
for the transition to occur in symmetric nuclear matter, whereas the the
transition in pure neutron matter occurs even in its absence. The behavior of
the isovector spin-longitudinal response and the pion excess in the vicinity of
the transition, and the model dependence of the transition are discussed.Comment: 44 pages RevTeX, 15 postscript figures. Minor modifications to
original postin
Contribution of the massive photon decay channel to neutrino cooling of neutron stars
We consider massive photon decay reactions via intermediate states of
electron-electron-holes and proton-proton-holes into neutrino-antineutrino
pairs in the course of neutron star cooling. These reactions may become
operative in hot neutron stars in the region of proton pairing where the photon
due to the Higgs-Meissner effect acquires an effective mass that
is small compared to the corresponding plasma frequency. The contribution of
these reactions to neutrino emissivity is calculated; it varies with the
temperature and the photon mass as
for . Estimates show that these processes appear as extra
efficient cooling channels of neutron stars at temperatures K.Comment: accepted to publication in Zh. Eksp. Teor. Fiz. (JETP
The decay and the coupling constant g
The experimental branching ratio for the radiative decay
is used to estimate the coupling constant
for a set of values of -meson parameters
M and . Our results are quite different than the
values of this constant used in the literature.Comment: 9 pages(RevTex), 5 ps figure
Reduced diversity and increased virulence-gene carriage in intestinal enterobacteria of coeliac children
<p>Abstract</p> <p>Background</p> <p>Coeliac disease is an immune-mediated enteropathology triggered by the ingestion of cereal gluten proteins. This disorder is associated with imbalances in the composition of the gut microbiota that could be involved in its pathogenesis. The aim of the present study was to determine whether intestinal <it>Enterobacteriaceae </it>populations of active and non-active coeliac patients and healthy children differ in diversity and virulence-gene carriage, so as to establish a possible link between the pathogenic potential of enterobacteria and the disease.</p> <p>Methods</p> <p><it>Enterobacteriaceae </it>clones were isolated on VRBD agar from faecal samples of 31 subjects (10 active coeliac patients, 10 symptom-free coeliac patients and 11 healthy controls) and identified at species level by the API 20E system. <it>Escherichia coli </it>clones were classified into four phylogenetic groups A, B1, B2 and D and the prevalence of eight virulence-associated genes (type-1 fimbriae [<it>fimA</it>], P fimbriae [<it>papC</it>], S fimbriae [<it>sfaD/E</it>], Dr haemagglutinin [<it>draA</it>], haemolysin [<it>hlyA</it>], capsule K1 [<it>neuB</it>], capsule K5 [<it>KfiC</it>] and aerobactin [<it>iutA</it>]) was determined by multiplex PCR.</p> <p>Results</p> <p>A total of 155 <it>Enterobacteriaceae </it>clones were isolated. Non-<it>E. coli </it>clones were more commonly isolated in healthy children than in coeliac patients. The four phylogenetic <it>E. coli </it>groups were equally distributed in healthy children, while in both coeliac patients most commensal isolates belonged to group A. Within the virulent groups, B2 was the most prevalent in active coeliac disease children, while D was the most prevalent in non-active coeliac patients. <it>E coli </it>clones of the virulent phylogenetic groups (B2+D) from active and non-active coeliac patients carried a higher number of virulence genes than those from healthy individuals. Prevalence of P fimbriae (<it>papC</it>), capsule K5 (<it>sfaD/E</it>) and haemolysin (<it>hlyA</it>) genes was higher in <it>E. coli </it>isolated from active and non-active coeliac children than in those from control subjects.</p> <p>Conclusion</p> <p>This study has demonstrated that virulence features of the enteric microbiota are linked to coeliac disease.</p
Muons and emissivities of neutrinos in neutron star cores
In this work we consider the role of muons in various URCA processes relevant
for neutrino emissions in the core region of neutron stars. The calculations
are done for --stable nuclear matter with and without muons. We find
muons to appear at densities fm, slightly around the
saturation density for nuclear matter fm. The direct URCA
processes for nucleons are forbidden for densities below
fm, however the modified URCA processes with muons ), where is a
nucleon, result in neutrino emissivities comparable to those from
). This
opens up for further possibilities to explain the rapid cooling of neutrons
stars. Superconducting protons reduce however these emissivities at densities
below fm.Comment: 14 pages, Revtex style, 3 uuencoded figs include
Phi Mesons from a Hadronic Fireball
Production of mesons is considered in the course of heavy-ion
collisions at SPS energies. We investigate the possible difference in momentum
distributions of mesons measured via their leptonic () and
hadronic () decays. Rescattering of secondary kaons in the dense hadron
gas together with the influence of in-medium kaon potential can lead to a
relative decrease of a yield observed in the hadronic channel. We
analyze how the in-medium modifications of meson properties affect apparent -
reconstructed momentum distributions of mesons. Quantitative results are
presented for central Pb+Pb collisions at .Comment: style Revtex4,9 pages, 5 figures. submitted to Phys. Rev.
Sideward flow of K+ mesons in Ru+Ru and Ni+Ni reactions near threshold
Experimental data on K+ meson and proton sideward flow measured with the FOPI
detector at SIS/GSI in the reactions Ru+Ru at 1.69 AGeV and Ni+Ni at 1.93 AGeV
are presented. The K+ sideward flow is found to be anti-correlated (correlated)
with the one of protons at low (high) transverse momenta. When compared to the
predictions of a transport model, the data favour the existence of an in-medium
repulsive K+ nucleon potential.Comment: 16 pages Revtex, 3 ps-figures, submitted to Phys. Lett.
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