5 research outputs found
Low-energy interaction of composite spin-half systems with scalar and vector fields
We consider a composite spin-half particle moving in spatially-varying scalar
and vector fields. The vector field is assumed to couple to a conserved charge,
but no assumption is made about either the structure of the composite or its
coupling to the scalar field. A general form for the piece of the spin-orbit
interaction of the composite with the scalar and vector fields which is
first-order in momentum transfer and second-order in the fields is
derived.Comment: 10 pages, RevTe
Chiral quark-soliton model in the Wigner-Seitz approximation
In this paper we study the modification of the properties of the nucleon in
the nucleus within the quark-soliton model. This is a covariant, dynamical
model, which provides a non-linear representation of the spontaneously broken
SU(2)_L X SU(2)_R symmetry of QCD. The effects of the nuclear medium are
accounted for by using the Wigner-Seitz approximation and therefore reducing
the complex many-body problem to a simpler single-particle problem. We find a
minimum in the binding energy at finite density, a change in the isoscalar
nucleon radius and a reduction of the in-medium pion decay constant. The latter
is consistent with a partial restoration of chiral symmetry at finite density,
which is predicted by other models.Comment: 30 pages, 13 figures; uses REVTeX and epsfi
Atomic Parity Nonconservation: Electroweak Parameters and Nuclear Structure
There have been suggestions to measure atomic parity nonconservation (PNC)
along an isotopic chain, by taking ratios of observables in order to cancel
complicated atomic structure effects. Precise atomic PNC measurements could
make a significant contribution to tests of the Standard Model at the level of
one loop radiative corrections. However, the results also depend upon certain
features of nuclear structure, such as the spatial distribution of neutrons in
the nucleus. To examine the sensitivity to nuclear structure, we consider the
case of Pb isotopes using various recent relativistic and non-relativistic
nuclear model calculations. Contributions from nucleon internal weak structure
are included, but found to be fairly negligible. The spread among present
models in predicted sizes of nuclear structure effects may preclude using Pb
isotope ratios to test the Standard Model at better than a one percent level,
unless there are adequate independent tests of the nuclear models by various
alternative strong and electroweak nuclear probes. On the other hand,
sufficiently accurate atomic PNC experiments would provide a unique method to
measure neutron distributions in heavy nuclei.Comment: 44 pages, INT Preprint DOE/ER/40561-050-INT92-00-1
Ghost Poles in the Nucleon Propagator: Vertex Corrections and Form Factors
Vertex corrections are taken into account in the Schwinger-Dyson equation for
the nucleon propagator in a relativistic field theory of fermions and mesons.
The usual Hartree-Fock approximation for the nucleon propagator is known to
produce the appearance of complex (ghost) poles which violate basic theorems of
quantum field theory. In a theory with vector mesons there are vertex
corrections that produce a strongly damped vertex function in the ultraviolet.
One set of such corrections is known as the Sudakov form factor in quantum
electrodynamics. When the Sudakov form factor generated by massive neutral
vector mesons is included in the Hartree-Fock approximation to the
Schwinger-Dyson equation for the nucleon propagator, the ghost poles disappear
and consistency with basic requirements of quantum field theory is recovered.Comment: 18 page