REINA() DE TRABALHO SOBRE FiSICA NUCLEAR NO BRASIL

XX RTFINIR Resumos
distances.
[1] G. Brown and D. W. Durso, Phys. Lett. 1335
(1971) 120
CHIRAL SYMMETRY AND
NUCLEON-NUCLEON SCATTERING
MANUEL ROBERT() ROBILOTTA
Institute de Fisica, Universidade de Silo Paula
JOEL CdSAR PEPIN
Institute de Fisica 'Tedrica, Universidade Estadual Paulista
We assume that the nucleon-nucleon interaction for low
and intermediate energies is given just by the exchanges
of one and two pions. In the latter case we adopt a
model based on chiral symmetry and subthreshold pionnucleon
interaction amplitude, which contains no free
parameters. Chiral symmetry is very relevant because
it is the responsible for the organization of various processes
into autonomous families. This gives rise to cancellations
in the intermediate pion-nucleon interaction,
which is the main building block of the nucleon-nucleon
interaction. The subthreshold pion-nucleon amplitude
is supplemented by empirical information in the form of
the Miler, Jacob and Strauss (HIS) coefficients. Predictions
from this model for nucleon-nucleon observables
are calculated in the momentum space and compared
with experimental data.
Null Plane Model of Proton
W. R. B. DE ARAXT.10, J. P. 13. C. DE MELD
Thstituto de Fisica, Universidade de Siio Paulo
T. FREDERIC°
Depto. de Fisica, ITA, Centro Tdcnieo Acrocspacial, Sao
Jose dos Campos, Siin Paulo
We present a calculation of the proton electric formfactor
(GB(9 2)), using a three quark Faddeev wavefunction
in the null-plane[1]. The null-plane wavefunction
is obtained from the solution of the Faddeev
equation with zero-range force acting between the constituent
quarks. No confinement is present in our effective
model. The totally symmetric spatial part of
the wave-function is obtained numerically in a threeboson
calculation. We use the covariance of the proton
model under kinematical front-form boosts to calculate
GE(q 2), and compare our numerical results with the
available experimental data. GE(q 2) scales with q4 in
the asymptotic region and describes the data for low
momentum transfers.
Our attempt, using such a schematical model, is based
on the notion of relativistic constituent quarks. We
have also seen examples in the literature [2], in which
the spontaneous breaking of chiral symmetry creates
the constituent quark mass. Such a mechanism is modeled
using the Nambu-Jona-Lasinio contact interaction
and applied to hadronic phenomenology.
Our schematical model has both ingredients together:
relativistic constituent quark and a contact interaction.
We test the totally symmetric spatial part of the proton
wave-function with these two minimal ingredients in a
calculation of the proton eletric form-factor. The confinement
has no explicit role in the model but is buried in
the effective degrees of freedom. Relativistic dynamics
is required by the mass of the constituent quarks and
the size of the nucleon wave-function. The reason for
choosing a three boson dynamics, is to just concentrate
on the specific form of the spatial wave-function, and
obtain insight in to it without the complications arising
with the use of the spin.
The relativistic spin structure is planned to be included
in our model through the Melosh rotation of the spins.
[3]-
References
[1] W.R.B. dc Araujo, J.P.D.0 de Melo and T.Prederico,
Phys. Rev. C52 (1995)2733.
[2] II.Vogl and W. Weise, Prog. Burl. Part. Phys, 27
(1991) 195.
[3] P.L.Chung and F. Coester, Phys. Rev. D44 (1991) 229.
Deformed algebras and chiral symmetry
breaking
VARESE SALVADOR TIIVIOTEO, CELSO LUIZ LIMA
IFUSP
In the beginning of the sixties, Nambu and Jona-Lasinio
proposed a model based in an analogy with the theory
of superconductivity [1]. Originally the Nambu—jona-
Lasinio model (NJL) was constructed as a pre-QCD
theory of nucleons that interact via an effective twobody
interaction. This model is reinterpreted today as
a theory with quarks degrees of freedom. The Lagrangian
of the NU model was constructed in such a way
that the symmetries of QCD are also part of it. One of
the most important of these symmetries is the chiral symmetry,
which is essential to the understanding of the
lightest hadrons and is spontaneously broken in QCD.
The NIL model is very useful for observing how these
things happen. In particular, the clynammic generation
of fermion masses brought about by the breaking
of chiral symmetry is one of the features of this model.
Our porpose is to simulate the explicit chiral symmetry
breaking by deforming the algebra of the model. This
idea was motivated by recent applications of q-deformed
algebras in nuclear structure problems. In this context,
for instance, the pairing in a single j shell, the spectra
of rotational nuclei and the phase transitions in the
Lipkin model were studied [2].
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