111 research outputs found
Scalar mesons nonet in a scaled effective Lagrangian
A scaled SU(3) Nambu - Jona-Lasinio Lagrangian is used to compute the mass of
the nine scalar mesons in the vacuum and the mass of the gluball. It is shown
that a suitable choice of the vacuum gluon condensate allows to reproduce the
experimental masses of the scalar mesons except for the {}(1430). This
choice corresponds to a weak coupling between the gluon and quark condensates,
giving a {}(1500) or a {}(1710) which is nearly a pure glueball.Comment: 12 pages, Latex, use elsart.st
Phase transition and thermodynamics of a hot and dense system in a scaled NJL model
The chiral phase transition of a hot and dense system of quarks is studied
within a modified SU(3) NJL lagrangian that implements the QCD scale anomaly.
The u- and s-quark condensates can feel or not the same chiral restoration
depending on the considered region of the 3-dimension space T_c(\mu_uc,\mu_sc).
The temperature behaviour of the pressure and of the energy and entropy
densities of the u- and s-quark system is investigated. At high temperature,
the non-vanishing bare s-quark mass only modifies slightly the usual behaviour
associated with an ideal quark gas.Comment: 23 pages, LaTeX, uses elsart.sty. This version of the paper includes
the figures (ps
The Valence Quark Distribution of the Pion
The pion structure function is investigated in a simple model, where the pion
and its constituent quark fields are coupled through the simplest pseudoscalar
coupling. The imaginary part of the forward gamma* pi -> gamma* pi scattering
amplitude is evaluated and related to the structure functions. It is shown that
the introduction of non-perturbative effects, linked to the size of the pion,
allows a connection with the quark distribution. It is predicted that
higher-twist terms become negligible for Q^2 larger than ~2 GeV^2, that quarks
in the pion have a momentum fraction smaller than in the proton case, and that
the momentum sum rule is violated for the pion.Comment: Presented by J. P. Lansberg at the XXII Physics in Collision
Conference (PIC02), Stanford, California, June 20-22, 2002, 3 pages, 4
figures, LaTeX, uses pic02.sty (included
A toy model for generalised parton distributions
We give the results of a simple model for the diagonal and off-diagonal
valence quark distributions of a pion. We show that structure can be
implemented in a gauge-invariant manner. This explicit model questions the
validityof the momentum sum rule, and gives an explicit counter-example to the
Wandzura-Wilczek ansatz for twist-3 GPD's.Comment: 11 pages, presented at HADRONIC PHYSICS (HLPR 2004): Joint
Meeting-Heidelberg-Liege-Paris-Rostock, Spa, Belgium, 16-18 December 2004, 11
pages, 11 figures, LaTe
Confinement and cut-off: a model for the pion quark distribution function
The pion structure function is investigated in a simple pseudo-scalar
coupling model of pion and constituent quark fields. The imaginary part of the
forward Compton scattering amplitude is evaluated. We show that the
introduction of non-perturbative effects, linked through a cut-off to the size
of the pion, allows the reproduction of important features of the pion quark
distribution function.Comment: 3 pages, 1 figur
Pion Structure Function and Violation of the Momentum Sum Rule
We present a method to evaluate the pion structure functions from a box
diagram calculation. Pion and constituent quark fields are coupled through the
simplest pseudoscalar coupling. The gamma^* pi -> q \bar q cross-section is
evaluated and related to the structure functions. We then show that the
introduction of non-perturbative effects, related to the pion size and
preserving gauge invariance, provides us with a straighforward relation with
the quark distribution. It is predicted that higher-twist terms become
negligible for Q^2 larger than about 2 GeV^2 and that quarks in the pion have a
momentum fraction smaller than in the proton. We enlarge the discussion
concerning this violation of the momentum sum rule, emphasizing that the sum
rule is recovered in the chiral limit and also when the finite size condition
is not imposed.Comment: Presented by J.P. Lansberg at the II International Workshop on Hadron
Physics, 25-29 September, 2002, Coimbra, Portugal, 14 pages, 9 figures,
LaTeX, uses aip-6s.clo, aipproc.cls and aipxfm.sty (included
A Model for the Pion Structure Function
The pion structure function is investigated in a simple model, where pion and
constituent quark fields are coupled through the simplest pseudoscalar
coupling. The imaginary part of the forward gamma* pi-> gamma* pi scattering
amplitude is evaluated and related to the structure functions. It is shown that
the introduction of non-perturbative effects, linked to the size of the pion
and preserving gauge invariance, allows a connection with the quark
distribution. It is predicted that higher-twist terms become negligible for Q2
larger than about 2 GeV2 and that quarks in the pion have a momentum fraction
smaller than in the proton case.Comment: 14 pages, 6 figures, LaTeX, elsart clas
On the relativistic origin of the kink effect in the chain of Pb isotopes
We investigate the origin of the kink effect (KE) in the relativistic mean
field theory by transforming the single-particle Dirac equation into a
Schrodinger-like equation. It is found that relativistic self-consistent
effects as well as contributions from the rho meson determine the actual
structure of the KE. However, the spin-orbit force generated by the rho meson
has no significant influence on the KE.Comment: 11 pages, RevTeX, 3 postscript figs., Phys. Lett.
Correlations and the relativistic structure of the nucleon self-energy
A key point of Dirac Brueckner Hartree Fock calculations for nuclear matter
is to decompose the self energy of the nucleons into Lorentz scalar and vector
components. A new method is introduced for this decomposition. It is based on
the dependence of the single-particle energy on the small component in the
Dirac spinors used to calculate the matrix elements of the underlying NN
interaction. The resulting Dirac components of the self-energy depend on the
momentum of the nucleons. At densities around and below the nuclear matter
saturation density this momentum dependence is dominated by the non-locality of
the Brueckner G matrix. At higher densities these correlation effects are
suppressed and the momentum dependence due to the Fock exchange terms is
getting more important. Differences between symmetric nuclear matter and
neutron matter are discussed. Various versions of the Bonn potential are
considered.Comment: 18 pages LaTeX, including 6 figure
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