23 research outputs found
Structure of the Vacuum in Nuclear Matter - A Nonperturbative Approach
We compute the vacuum polarisation correction to the binding energy of
nuclear matter in the Walecka model using a nonperturbative approach. We first
study such a contribution as arising from a ground state structure with
baryon-antibaryon condensates. This yields the same results as obtained through
the relativistic Hartree approximation of summing tadpole diagrams for the
baryon propagator. Such a vacuum is then generalized to include quantum effects
from meson fields through scalar-meson condensates. The method is applied to
study properties of nuclear matter and leads to a softer equation of state
giving a lower value of the incompressibility than would be reached without
quantum effects. The density dependent effective sigma mass is also calculated
including such vacuum polarisation effects.Comment: 26 pages including 5 eps files, uses revtex style; PACS number:
21.65.+f,21.30.+
Chiral Lagrangian for strange hadronic matter
A generalized Lagrangian for the description of hadronic matter based on the
linear -model is proposed. Besides the baryon
octet, the spin-0 and spin-1 nonets, a gluon condensate associated with broken
scale invariance is incorporated. The observed values for the vacuum masses of
the baryons and mesons are reproduced. In mean-field approximation, vector and
scalar interactions yield a saturating nuclear equation of state. We discuss
the difficulties and possibilities to construct a chiral invariant baryon-meson
interaction that leads to a realistic equation of state. It is found that a
coupling of the strange condensate to nucleons is needed to describe the
hyperon potentials correctly. The effective baryon masses and the appearance of
an abnormal phase of nearly massless nucleons at high densities are examined. A
nonlinear realization of chiral symmetry is considered, to retain a Yukawa-type
baryon-meson interaction and to establish a connection to the Walecka-model.Comment: Revtex, submitted to Phys. Rev.
Phase Transition in the chiral - model with dilatons
We investigate the properties of different modifications to the linear
-model (including a dilaton field associated with broken scale
invariance) at finite baryon density and nonzero temperature . The
explicit breaking of chiral symmetry and the way the vector meson mass is
generated are significant for the appearance of a phase of nearly vanishing
nucleon mass besides the solution describing normal nuclear matter. The
elimination of the abnormal solution prohibits the onset of a chiral phase
transition but allows to lower the compressibility to a reasonable range. The
repulsive contributions from the vector mesons are responsible for the wide
range of stability of the normal phase in the -plane. The abnormal
solution becomes not only energetically preferable to the normal state at high
temperature or density, but also mechanically stable due to the inclusion of
dilatons.Comment: 21 pages, RevTe