381 research outputs found
Analytic structure of meson propagators in the proper-time regularized Nambu--Jona-Lasinio model
We analyze the analytic structure of meson propagators in the
Nambu--Jona-Lasinio model with a proper-time regulator. We show that the
regulator produces unphysical complex singularities. As a result the naive use
of the Wick rotation is no longer allowed. Formulas involving integration over
mesonic momenta, such as meson-loop contributions or dispersion relations for
meson Green's functions, cannot be written in usual forms.Comment: revised versio
On nucleon exchange mechanism in heavy-ion collisions at near-barrier energies
Nucleon drift and diffusion mechanisms in central collisions of asymmetric
heavy-ions at near-barrier energies are investigated in the framework of a
stochastic mean-field approach. Expressions for diffusion and drift
coefficients for nucleon transfer deduced from the stochastic mean-field
approach in the semiclassical approximation have similar forms familiar from
the phenomenological nucleon exchange model. The variance of fragment mass
distribution agrees with the empirical formula . The comparison with the time-dependent Hartree-Fock calculations
shows that, below barrier energies, the drift coefficient in the semiclassical
approximation underestimates the mean number of nucleon transfer obtained in
the quantal framework. Motion of the window in the dinuclear system has a
significant effect on the nucleon transfer in asymmetric collisions.Comment: 10 pages, 10 figures, submitted for publicatio
Electromagnetic properties of the Delta(1232) and decuplet baryons in the self-consistent SU(3) chiral quark-soliton model
We examine the electromagnetic properties of the Delta(1232) resonance within
the self-consistent chiral quark-soliton model. In particular we present the
Delta form factors of the vector-current GE0, GE2 and GM1 for a
momentum-transfer range of . We apply the
symmetry-conserving quantization of the soliton and take 1/N_c rotational
corrections into account. Values for the magnetic moments of all decuplet
baryons as well as for the N-Delta transition are given. Special interest is
also given to the electric quadrupole moment of the Delta.Comment: 24 pages, 8 figure
Mass dispersion in transfer reactions with a stochastic mean-field theory
Nucleon transfer in symmetric heavy-ion reactions at energies below the
Coulomb barrier is investigated in the framework of a microscopic stochastic
mean-field theory. While mean-field alone is known to significantly
underpredict the dispersion of the fragment mass distribution, a considerable
enhancement of the dispersion is obtained in the stochastic mean-field theory.
The variance of the fragment mass distribution deduced from the stochastic
theory scales with the number of exchanged nucleon. Therefore, the new approach
provides the first fully microscopic theory consistent with the
phenomenological analysis of the experimental data.Comment: 4 pages, 2 figures, 1 tabl
Weak electricity of the Nucleon in the Chiral Quark-Soliton Model
The induced pseudotensor constant (weak electricity) of the nucleon is
calculated in the framework of the chiral quark soliton model. This quantity
originates from the G-parity violation and hence is proportional to .
We obtain for a value of .Comment: The final version. Accepted for publication in Phys. Rev.
The Skyrme energy functional and low lying 2+ states in Sn, Cd and Te isotopes
We study the predictive power of Skyrme forces with respect to low lying
quadrupole spectra along the chains of Sn, Cd, and Te isotopes. Excitation
energies and B(E2) values for the lowest quadrupole states are computed from a
collective Schroedinger equation which as deduced through collective path
generated by constraint Skyrme-Hartree-Fock (SHF) plus self-consistent cranking
for the dynamical response. We compare the results from four different Skyrme
forces, all treated with two different pairing forces (volume versus
density-dependent pairing). The region around the neutron shell closure N=82 is
very sensitive to changes in the Skyrme while the mid-shell isotopes in the
region N<82 depend mainly on the adjustment of pairing. The neutron rich
isotopes are most sensitive and depend on both aspects
Positivity bounds on generalized parton distributions in impact parameter representation
New positivity bounds are derived for generalized (off-forward) parton
distributions using the impact parameter representation. These inequalities are
stable under the evolution to higher normalization points. The full set of
inequalities is infinite. Several particular cases are considered explicitly.Comment: 8 page
Nuclear Giant Resonances and Linear Response
We search for nonlinear effects in nuclear giant resonances (GRs), in
particular the isovector dipole and the isoscalar quadrupole modes. To that
end, we employ a spectral analysis of time-dependent Hartree-Fock (TDHF)
dynamics using Skyrme forces. Based on TDHF calculations over a wide range of
excitation amplitudes, we explore the collectivity and degree of harmonic
motion in these modes. Both GR modes turn out to be highly harmonic in heavy
nuclei from A=100 on. There is no trace of a transition to irregular motion and
multiple resonances are predicted. Slight anharmonicities are seen for light
nuclei, particularly for O. These are mainly caused by the spin-orbit
splitting.Comment: 5 page
Octet, decuplet and antidecuplet magnetic moments in the chiral quark soliton model revisited
We reanalyse the magnetic moments of the baryon octet, decuplet, and
antidecuplet within the framework of the chiral quark-soliton model, with SU(3)
symmetry breaking taken into account. We consider the contributions of the
mixing of higher representations to the magnetic moment operator arising from
the SU(3) symmetry breaking. Dynamical parameters of the model are fixed by
experimental data for the magnetic moments of the baryon octet and from the
masses of the octet, decuplet and of . The magnetic moment of
depends rather strongly on the pion-nucleon sigma term and reads
to for and 75 MeV
respectively. The recently reported mass of is
compatible with MeV. As a byproduct the strange magnetic
moment of the nucleon is obtained with a value of n.m.Comment: RevTeX is used. 12 pages, 3 figures, final version for publication in
Phys. Rev.
Electromagnetic Form Factors of the SU(3) Octet Baryons in the semibosonized SU(3) Nambu-Jona-Lasinio Model
The electromagnetic form factors of the SU(3) octet baryons are investigated
in the semibosonized SU(3) Nambu--Jona-Lasinio model (chiral quark-soliton
model). The rotational and strange quark mass corrections in linear
order are taken into account. The electromagnetic charge radii of the nucleon
and magnetic moments are also evaluated. It turns out that the model is in a
remarkable good agreement with the experimental data.Comment: RevTex is used. 37 pages. The final version to appear in Phys. Rev.
D. 13 figures are include
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