369 research outputs found
The nuclear pseudospin symmetry along an isotopic chain
We investigate the isospin dependence of pseudospin symmetry in the chain of
tin isotopes (from Sn until Sn). Using a Woods-Saxon
parametrization of the nuclear potential for these isotopes we study in detail
the effect of the vector-isovector and Coulomb potentials in the energy
splittings of neutron and proton pseudospin partners in the isotopic chain. We
conclude that the realization of nuclear pseudospin symmetry does not change
considerably with the mass number, and is always favored for neutrons. We also
find that the potential accounts for essentially all the pseudospin
isospin asymmetry observed and that the Coulomb potential plays a negligible
role in this asymmetry. This can be explained by the dynamical nature of
pseudospin symmetry in nuclei, namely the dependence of the pseudospin
splittings on the shape of the nuclear mean-field potential.Comment: 4 pages, 4 figures, to be published in Brazilian Journal of Physic
Dynamical nature of the nuclear pseudospin and its isospin asymmetry
Pseudospin symmetry in nuclei is investigated by solving the Dirac equation
with Woods-Saxon scalar and vector radial potentials. We relate the pseudospin
interaction with a pseudospin-orbit term in a Schroedinger-like equation for
the lower component of the Dirac spinor. We show that this term gives a large
contribution to the energy splittings of pseudospin partners, so that the near
pseudospin degeneracy arises from a significant cancellation among the
different terms in that equation. This is a manifestation of the dynamical
character of this symmetry in the nucleus. We analyze the isospin dependence of
the pseudospin symmetry in a nuclear isotope chain by including a
vector-isovector potential V_rho and a Coulomb potential and conclude that
V_rho gives the main contribution to the observed pseudospin isospin asymmetry.Comment: 4 pages, 2 figures, uses World Scientific style file. Contribution
presented at the VIII International Workshop on Hadron Physics, Bento
Goncalves, RS, Brazil, April 14-19, 2002. To be published by World Scientific
in the proceedings of the "International Workshop on Hadron Physics 2002
Tensor coupling and pseudospin symmetry in nuclei
In this work we study the contribution of the isoscalar tensor coupling to
the realization of pseudospin symmetry in nuclei. Using realistic values for
the tensor coupling strength, we show that this coupling reduces noticeably the
pseudospin splittings, especially for single-particle levels near the Fermi
surface. By using an energy decomposition of the pseudospin energy splittings,
we show that the changes in these splittings come by mainly through the changes
induced in the lower radial wave function for the low-lying pseudospin
partners, and by changes in the expectation value of the pseudospin-orbit
coupling term for surface partners. This allows us to confirm the conclusion
already reached in previous studies, namely that the pseudospin symmetry in
nuclei is of a dynamical nature.Comment: 11 pages, 5 figures, uses REVTeX macro
White dwarfs with a surface electrical charge distribution: Equilibrium and stability
The equilibrium configuration and the radial stability of white dwarfs
composed of charged perfect fluid are investigated. These cases are analyzed
through the results obtained from the solution of the hydrostatic equilibrium
equation. We regard that the fluid pressure and the fluid energy density follow
the relation of a fully degenerate electron gas. For the electric charge
distribution in the object, we consider that it is centralized only close to
the white dwarfs' surfaces. We obtain larger and more massive white dwarfs when
the total electric charge is increased. To appreciate the effects of the
electric charge in the structure of the star, we found that it must be in the
order of with which the electric field is about
. For white dwarfs with electric fields close to the
Schwinger limit, we obtain masses around . We also found that in
a system constituted by charged static equilibrium configurations, the maximum
mass point found on it marks the onset of the instability. This indicates that
the necessary and sufficient conditions to recognize regions constituted by
stable and unstable equilibrium configurations against small radial
perturbations are respectively and .Comment: This is a preprint. The original paper will be published in EPJ
Small quark stars in the chromodielectric model
Equations of state for strange quark matter in beta equilibrium at high
densities are used to investigate the structure (mass and radius) of compact
objects. The chromodielectric model is used as a general framework for the
quark interactions, which are mediated by chiral mesons, and , and by a confining chiral singlet dynamical field, . Using a
quartic potential for , two equations of state for the same set of model
parameters are obtained, one with a minimum at around the nuclear matter
density and the other at . Using the latter
equation of state in the Tolman-Oppenheimer-Volkoff equations we found
solutions corresponding to compact objects with km and . The phenomenology of recently discovered X-ray sources is compatible
with the type of quark stars that we have obtained.Comment: 8 pages, AIP macros; Talk delivered at the Pan American Advanced
Studies Institute (PASI) Conference "New States of Matter in Hadronic
Interactions", Campos do Jordao, Brazil, January 200
- …