25 research outputs found
Quark and pion effective couplings from polarization effects
A flavor SU(2) effective model for pions and quarks is derived by considering
polarization effects departing from the usual quark-quark effective interaction
induced by dressed gluon exchange, i.e. a global color model for QCD. For that,
the quark field is decomposed into a component that yields light mesons and the
quark-antiquark condensate, being integrated out by means of the auxiliary
field method, and another component which yields constituent quarks, which is
basically a background quark field. Within a longwavelength and weak quark
field expansion (or large quark effective mass expansion) of a quark
determinant, the leading terms are found up to the second order in a zero order
derivative expansion, by neglecting vector mesons that are considerably heavier
than the pion. Pions are considered in the structureless limit and, besides the
chiral invariant terms that reproduce previously derived expressions, symmetry
breaking terms are also presented. The leading chiral quark-quark effective
couplings are also found corresponding to a NJL and a vector-NJL couplings. All
the resulting effective coupling constants and parameters are expressed in
terms of the current and constituent quark masses and of the coupling .Comment: 20 pages, revised version to be published in Eur. Phys. Journ.
Pion Mass Dependence of Nucleon Magnetic Moments
The relevance of the pion mass, provenient from a term which explicitely
breaks chiral symmetry in the Lagrangian, for nucleon magnetic moment in the
frame of the Skyrmion model in two different versions: the usual Skyrme model
and a modified one which includes a coupling to a light scalar meson field, the
sigma MeV). The results are compared to other
calculations. Our main motivation comes from usual extrapolations for values of
low energy QCD observables obtained in lattices with large values of pion/quark
masses toward realistic value of . which do not allow it. We do a
comparison with results from the Cloudy Bag Model and a chiral hadronic model
from chiral perturbation theory. There are several resulting extrapolations
from the region of large pion mass to the realistic value depending on the
considered model for low energy QCD.Comment: five pages, Contribution for the Proceedings of the Meeting on
Hadronic Interactions, Mackenzie University, S\~ao Paulo, SP, Brazil, May
200
Pion constituent quarks couplings strong form factors: a dynamical approach
Form factors for pions interactions with constituent quarks are investigated
as the leading effective couplings obtained from a one loop background field
method applied to a global color model. Two pion field definitions are
considered and the resulting eleven form factors are expressed in terms of
components of the quark and gluon propagators that compose only two momentum
dependent functions. A momentum dependent Goldberger Treiman relation is also
obtained as one of the ratios between the form factors. The resulting form
factors with pion momenta up to 1.5 GeV are exhibited for different quark
effective masses and two different non-perturbative gluon propagators and they
present similar behavior to fittings of experimental data from nucleons form
factors. The corresponding pseudoscalar averaged quadratic radii (a.q.r.) and
correction to the axial a.q.r. are presented as functions of the sea quark
effective mass, being equal respectively to the scalar and vector ones at the
present level of calculation.Comment: 25 pages, 12 figures, revised versio