211 research outputs found
Baryons in the Field Correlator Method: Effects of the Running Strong Coupling
The ground and P-wave excited states of nnn, nns and ssn baryons are studied
in the framework of the Field Correlator Method using the running strong
coupling constant in the Coulomb-like part of the three-quark potential. The
running coupling is calculated up to two loops in the background perturbation
theory. The three-quark problem has been solved using the hyperspherical
functions method. The masses of the S- and P-wave baryons are presented. Our
approach reproduces and improves the previous results for the baryon masses
obtained for the freezing value of the coupling constant. The string correction
for the confinement potential of the orbitally excited baryons, which is the
leading contribution of the proper inertia of the rotating strings, is
estimated.Comment: 13 pages, 1 figure, 5 table
Chiral symmetry restoration in excited hadrons, quantum fluctuations, and quasiclassics
In this paper, we discuss the transition to the semiclassical regime in
excited hadrons, and consequently, the restoration of chiral symmetry for these
states. We use a generalised Nambu-Jona-Lasinio model with the interaction
between quarks in the form of the instantaneous Lorentz-vector confining
potential. This model is known to provide spontaneous breaking of chiral
symmetry in the vacuum via the standard selfenergy loops for valence quarks. It
has been shown recently that the effective single-quark potential is of the
Lorentz-scalar nature, for the low-lying hadrons, while, for the high-lying
states, it becomes a pure Lorentz vector and hence the model exhibits the
restoration of chiral symmetry. We demonstrate explicitly the quantum nature of
chiral symmetry breaking, the absence of chiral symmetry breaking in the
classical limit as well as the transition to the semiclassical regime for
excited states, where the effect of chiral symmetry breaking becomes only a
small correction to the classical contributions.Comment: RevTeX4, 20 pages, 4 Postscript figures, uses epsfig.sty, typos
correcte
Baryon magnetic moments in the effective quark Lagrangian approach
An effective quark Lagrangian is derived from first principles through
bilocal gluon field correlators. It is used to write down equations for
baryons, containing both perturbative and nonperturbative fields. As a result
one obtains magnetic moments of octet and decuplet baryons without introduction
of constituent quark masses and using only string tension as an input. Magnetic
moments come out on average in reasonable agreement with experiment, except for
nucleons and . The predictions for the proton and neutron are shown
to be in close agreement with the empirical values once we choose the string
tension such to yield the proper nucleon mass. Pionic corrections to the
nucleon magnetic moments have been estimated. In particular, the total result
of the two-body current contributions are found to be small. Inclusion of the
anomalous magnetic moment contributions from pion and kaon loops leads to an
improvement of the predictions.Comment: 24 pages Revte
On Goldstone bosons decoupling from high-lying hadrons
In this paper, we discuss a decoupling of the Goldstone bosons from highly
excited hadrons in relation to the restoration of chiral symmetry in such
hadrons. We use a generalised Nambu-Jona-Lasinio model with the interaction
between quarks in the form of an instantaneous Lorentz-vector confining
potential. This model is known to provide spontaneous breaking of chiral
symmetry in the vacuum via the standard selfenergy loops for valence quarks.
For highly excited hadrons, where the typical momentum of valence quarks is
large, the loop contributions represent only a small correction to the
chiral-invariant classical contributions and asymptotically vanish.
Consequently the chiral symmetry violating Lorentz-scalar dynamical mass of
quarks vanishes. Then the conservation of the axial vector current in the
chiral limit requires, via the Goldberger-Treiman relation, that the valence
quarks decouple from the Goldstone boson. As a consequence, the whole hadron
decouples from the Goldstone boson as well, which implies that its axial
constant also vanishes.Comment: RevTeX4, 21 pages, 5 Postscript figures, uses epsfig.sty, new chapter
with numerical estimates added, to appear in Phys.Rev.
Gauge-invariant gluon mass, infrared Abelian dominance and stability of magnetic vacuum
We give an argument for deriving analytically the infrared ``Abelian''
dominance in a gauge invariant way for the Wilson loop average in SU(2)
Yang--Mills theory. In other words, we propose a possible mechanism for
realizing the dynamical Abelian projection in the SU(2) gauge-invariant manner
without breaking color symmetry. This supports validity of the dual
superconductivity picture for quark confinement. We also discuss the stability
of the vacuum with magnetic condensation as a by-product of this result.Comment: 25 pages, 3 figures (4 eps files); version accepted for publication
in Phys.Rev.D; One paragraph is added at each end of sections 3,4 and 5 for
comparing the analytical result with the lattice results of my group based on
the new formulation, together with the results in the conventional MAG if
available. footnote 4 is added, and a reference is added. A number of
sentences and phrases are improve
Interaction of Wilson loops in confining vacuum
Nonperturbative and perturbative interaction mechanisms of Wilson loops in
gluodynamics are studied within the background field formalism. The first one
operates when distance between minimal surfaces of the loops is small and may
be important for sea quark effects and strong decay processes. The second
mechanism -- perturbative interaction in nonperturbative confining background
is found to be physically dominant for all loop configurations characteristic
of scattering process. It reduces to perturbative gluon exchanges at small
distances, while at larger distances it corresponds to the t-channel exchange
of (reggeized) glueball states.
Comparison to other approaches is made and possible physical applications are
discussed.Comment: LaTeX, 25 pages, 5 EPS-figure
Central exclusive production of scalar \chi_c meson at the Tevatron, RHIC and LHC energies
We calculate several differential distributions for exclusive double
diffractive production in proton-antiproton collisions at the
Tevatron and in proton-proton collisions at RHIC and LHC in terms of
unintegrated gluon distributions (UGDFs) within the -factorisation
approach. The uncertainties of the Khoze-Martin-Ryskin approach are discussed
in detail. The transition vertex is calculated as
a function of gluon virtualities applying the standard pNRQCD technique. The
off-shell effects are discussed and quantified. They lead to a reduction of the
cross section by a factor 2--5, depending on the position in the phase space
and UGDFs. Different models of UGDFs are used and the results are shown and
discussed. The cross section for diffractive component depends strongly on
UGDFs. We calculate also the differential distributions for the fusion mechanism. The integrated cross section for
photon-photon fusion is much smaller than that of diffractive origin. The two
components have very different dependence on momentum transfers in
the nucleon lines as well as azimuthal-angle correlations between both outgoing
nucleons.Comment: 34 pages, 23 figures, 2 table
Baryon magnetic moments in the QCD string approach
Magnetic moments of baryons composed of light and strange quarks are computed
for the first time through the only parameter of the model -- string tension
. Resulting theoretical values differ from the experimental ones
typically by about
10%.Comment: LaTeX, 13 pages; misprints are correcte
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