575 research outputs found
Ultraslow light propagation in an inhomogeneously broadened rare-earth ion-doped crystal
We show that Coherent Population Oscillations effect allows to burn a narrow
spectral hole (26Hz) within the homogeneous absorption line of the optical
transition of an Erbium ion-doped crystal. The large dispersion of the index of
refraction associated with this hole permits to achieve a group velocity as low
as 2.7m/s with a ransmission of 40%. We especially benefit from the
inhomogeneous absorption broadening of the ions to tune both the transmission
coefficient, from 40% to 90%, and the light group velocity from 2.7m/s to
100m/s
Proton Sea Quark Flavour Asymmetry and Roper Resonance
We study the proton and the Roper resonance together with the meson cloud
model, by constructing a Hamiltonian matrix and solving the eigenvalue
equation. The proton sea quark flavour asymmetry and some properties of the
Roper resonance are thus reproduced in one scheme
Principle of Balance and the Sea Content of the Proton
In this study, the proton is taken as an ensemble of quark-gluon Fock states.
Using the principle of balance that every Fock state should be balanced with
all of the nearby Fock states (denoted as the balance model), instead of the
principle of detailed balance that any two nearby Fock states should be
balanced with each other (denoted as the detailed balance model), the
probabilities of finding every Fock state of the proton are obtained. The
balance model can be taken as a revised version of the detailed balance model,
which can give an excellent description of the light flavor sea asymmetry
(i.e., ) without any parameter. In case of
sub-processes not considered, the balance model and the
detailed balance model give the same results. In case of
sub-processes considered, there is about 10 percent difference between the
results of these models. We also calculate the strange content of the proton
using the balance model under the equal probability assumption.Comment: 32 latex pages, 4 ps figures, to appear in PR
Flavor and Charge Symmetry in the Parton Distributions of the Nucleon
Recent calculations of charge symmetry violation(CSV) in the valence quark
distributions of the nucleon have revealed that the dominant symmetry breaking
contribution comes from the mass associated with the spectator quark
system.Assuming that the change in the spectator mass can be treated
perturbatively, we derive a model independent expression for the shift in the
parton distributions of the nucleon. This result is used to derive a relation
between the charge and flavor asymmetric contributions to the valence quark
distributions in the proton, and to calculate CSV contributions to the nucleon
sea. The CSV contribution to the Gottfried sum rule is also estimated, and
found to be small
Chiral Quark Model with Configuration Mixing
The implications of one gluon exchange generated configuration mixing in the
Chiral Quark Model (QM) with SU(3) and axial U(1) symmetry
breakings are discussed in the context of proton flavor and spin structure as
well as the hyperon -decay parameters. We find that QM
with SU(3) symmetry breaking is able to give a satisfactory unified fit for
spin and quark distribution functions, with the symmetry breaking parameters
, and the mixing angle , both for NMC and the
most recent E866 data. In particular, the agreement with data, in the case of
, F, D, and , is quite striking.Comment: 16 pages, LaTex, Table and Appendix adde
Octet Baryon Magnetic Moments in the Chiral Quark Model with Configuration Mixing
The Coleman-Glashow sum-rule for magnetic moments is always fulfilled in the
chiral quark model, independently of SU(3) symmetry breaking. This is due to
the structure of the wave functions, coming from the non-relativistic quark
model. Experimentally, the Coleman-Glashow sum-rule is violated by about ten
standard deviations. To overcome this problem, two models of wave functions
with configuration mixing are studied. One of these models violates the
Coleman-Glashow sum-rule to the right degree and also reproduces the octet
baryon magnetic moments rather accurately.Comment: 22 pages, RevTe
The Flavor Asymmetry of the Nucleon Sea
We re-examine the effects of anti-symmetry on the anti-quarks in the nucleon
sea arising from gluon exchange and pion exchange between confined quarks.
While the effect is primarily to suppress anti-down relative to anti-up quarks,
this is numerically insignificant for the pion terms.Comment: To appear in Phys. Rev.
Unified description of light- and strange-baryon spectra
We present a chiral constituent quark model for light and strange baryons
providing a unified description of their ground states and excitation spectra.
The model relies on constituent quarks and Goldstone bosons arising as
effective degrees of freedom of low-energy QCD from the spontaneous breaking of
chiral symmetry. The spectra of the three-quark systems are obtained from a
precise variational solution of the Schr\"odinger equation with a
semirelativistic Hamiltonian. The theoretical predictions are found in close
agreement with experiment.Comment: 9 pages, including 2 figure
Pion Content of the Nucleon as seen in the NA51 Drell-Yan experiment
In a recent CERN Drell-Yan experiment the NA51 group found a strong asymmetry
of and densities in the proton at . We interpret
this result as a decisive confirmation of the pion-induced sea in the nucleon.Comment: 10 pages + 3 figures, Preprint KFA-IKP(TH)-1994-14 .tex file. After
\enddocument a uu-encodeded Postscript file comprising the figures is
appende
Nucleon spin-flavor structure in SU(3) breaking chiral quark model
The SU(3) symmetric chiral quark model, which describes interactions between
quarks, gluons and the Goldstone bosons, explains reasonably well many aspects
of the flavor and spin structure of the proton, except for the values of
and . Introducing the SU(3)-breaking effect
suggested by the mass difference between the strange and nonstrange quarks, we
find that this discrepancy can be removed and better overall agreement
obtained.Comment: 18 pages, Latex, 4 tables. Phys. Rev. D (in press, submitted/revised
in June/Nov 1996
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