REINA() DE TRABALHO SOBRE FiSICA NUCLEAR NO BRASIL

24 Estrutura Nuclear - XX RTFNB
of the several characteristic nuclear matter parameters
such as volume energy, a o saturation density, pe , incompressibility,
K symmetry energy, J, as well as other
higher order parameters, like, L, K' and K, 5,,,. For
the density dependent RMF parameterization the analytical
expressions of these coefficients arc obtained for
the first time.
From the obtained results it is shown that non-linear
forces reproduce reasonably well the semi-empirical results,
while the density dependent approach provide an
unexpected small value for the incompressibility although
giving a better value for the symmetry energy.
The advantage of this last. approach is the elimination
of non-linear terms (which are of difficult physical interpretation)
and also to give a parameter free description
of the nuclear interaction, since the density dependence
of the coupling constants is fitted to Brueckner-Flatree-
Pock calculations for nuclear matter. The fact that we
get a too small incompressibility points out that the
used dependence (the single one available in the literature)
needs to be improved.
Density Dependent Relativistic Mean Field
Calculations for Semi-infinite Nuclear Matter
WELLINGTON GOMES DANTAS, MARIA LUIZA
CESCATO
UFPB
In the last years a density dependent Relativistic Mean
Field (RMF) approach has been proposed and applied
for the description of spherical and deformed nuclei. A
motivation for this description is to avoid the introduction
of non-linear, not well understood, self-interaction
terms in the cr7field, which are needed in order to achieve
a quantitative reproduction of nuclear surface properties.
The recent studies applying the density dependent approach
to infinite nuclear matter have shown that a too
low incompressibility is obtained, although a better value
for the symmetry energy is obtained. On the other
hand, the density dependent studies for deformed nuclei
have shown that a poor description of deformation
is obtained in this approach. These results were interpreted
as an indication that the density dependence of
the coupling constants available in the literature and
used in these works cannot well reproduce nuclear surface
properties.
In the present work we examine directly this point performing
Thomas-Fermi density dependent relativistic
mean field calculations for semi-infinite asymmetric nuclear
matter. The e — p-Walecka model is used and
the characteristic surface parameters for symmetric and
asymmetric nuclear matter are obtained. The results
are compared with semi-empirical mass formulae parameters
and also with the results of the usual linear and
non-linear RMF parameterization.
A RELATIVISTIC SEPARABLE
POTENTIAL TO DESCRIBE PAIRING IN
NUCLEAR MATTER
B. V. CARLSON, T. FREDERICO
Institute TecnolOgico de Aerondutica - CTA
F. B. GUIMARAES
EAN-N Institute dc Estudos Avangados - CTA
In two recent works[1,2], we have extended the usual
relativistic mean-field approximation to Quantum Hadrodynamics
(QHD) for the study of the short range
correlations in nuclear matter. These correlations have
been found to be rather simply related with the pairing
phenomenon between nucleons. This happens due to
the domination of the of the scattering N-N T-matrix
pole over the size of the pairing gap and, also, due to
the connection between the pairing field at low baryon
densities and the 1 80 N-N bound/virtual state wave
function. This simplicity suggests that a simple though
precise formulation of the nuclear pairing phenomenon
can he done by an approximation that adequately take
these results into account.
In this work we propose a separable approximation for
the pairing potential in nuclear matter, which correctly
takes into account the high momentum contributions of
the short range NN-correlations and is much easier to
handle than the complete set of the relativistic Hartree-
Fock-Bogolinbov(11F13)-field equations. The approximation
is based on the properties of the relativistic pairing
field in the zero baryon density limit (vacuum) and
on the observed numerical correlation between the magnitude
of the T-matrix pole and the size of the pairing
field for finite baryon densities.
The determination of the separable potential depends
on the precision which can be achieved for the determination
of the components of the vertex-function field
r(k). We have compared the usual relativistic
11PB-calculations for A with the corresponding separable
potential results, and the calculations for various
(ow)-potentials indicate that the above prescription is
adequate. The relativistic separable potential correctly
yields either the gap parameter, A9 , or the two bigger
components of the A field, A0 and A,, at all baryon
densities.
[1] F.B.Guirnaries, B.V.Carlson, and T.Frederico,
Phys. Rev. C 54, 2385 (1996).
[2]B.V.Carlson, T.Frederico and F.B.Guimaries, submitted
to Phys. Rev. C .