1,231 research outputs found
On the physics behind the form factor ratio
We point out that there exist two natural definitions of the nucleon
magnetization densities : the density introduced in Kelly's
phenomenological analysis and theoretically more standard one . We
can derive an explicit analytical relation between them, although Kelly's
density is more useful to disentangle the physical origin of the different
dependence of the Sachs electric and magnetic form factors of the
nucleon. We evaluate both of and as well as the
charge density of the proton within the framework of the chiral
quark soliton model, to find a noticeable qualitative difference between
and , which is just consistent with Kelly's result
obtained from the empirical information on the Sachs electric and magnetic form
factors of the proton.Comment: 12 pages, 5 figures. version to appear in J. Phys. G.: Nucl. Part.
Phy
Field dynamics and kink-antikink production in rapidly expanding systems
Field dynamics in a rapidly expanding system is investigated by transforming
from space-time to the rapidity - proper-time frame. The proper-time dependence
of different contributions to the total energy is established. For systems
characterized by a finite momentum cut-off, a freeze-out time can be defined
after which the field propagation in rapidity space ends and the system decays
into decoupled solitons, antisolitons and local vacuum fluctuations. Numerical
simulations of field evolutions on a lattice for the (1+1)-dimensional
model illustrate the general results and show that the freeze-out time and
average multiplicities of kinks (plus antikinks) produced in this 'phase
transition' can be obtained from simple averages over the initial ensemble of
field configurations. An extension to explicitly include additional dissipation
is discussed. The validity of an adiabatic approximation for the case of an
overdamped system is investigated. The (3+1)-dimensional generalization may
serve as model for baryon-antibaryon production after heavy-ion collisions.Comment: 18 pages, 7 figures. Two references added. New subsection III.E
added. Final version accepted for publication in PR
Towards a practical approach for self-consistent large amplitude collective motion
We investigate the use of an operatorial basis in a self-consistent theory of
large amplitude collective motion. For the example of the
pairing-plus-quadrupole model, which has been studied previously at
equilibrium, we show that a small set of carefully chosen state-dependent basis
operators is sufficient to approximate the exact solution of the problem
accuratly. This approximation is used to study the interplay of quadrupole and
pairing degrees of freedom along the collective path for realistic examples of
nuclei. We show how this leads to a viable calculational scheme for studying
nuclear structure, and discuss the surprising role of pairing collapse.Comment: 19 pages, 8 figures Revised version To be published in Phys. Rev.
Skyrmions and Bags in the 2D-O(3) model
Localized static solutions of the 2D-O(3) model are investigated in a
representation with the 3-vector field split into the unit vector
and the modulus . As in the nonlinear version of the model
this allows for the definition of a topological winding number , and for the
separation of the complete configuration space into distinct -sectors. For
small values of the -coupling strength the stable energy minima in
these sectors are characterized by bag formation in the modulus field which in
the standard cartesian representation of the linear O(3) model would be
unstable towards decay into the trivial B=0 vacuum. Stabilized by
-conservation they exhibit a surprising variety of very appealing features
for multiply charged systems. With the total charge bound into one common deep
bag opposite ways of distributing the topological charge density inside the bag
can be realized: Pointlike structures which retain the individuality of single
constituents (or doubly charged pairs), or a deconfined charge density spread
uniformly throughout the interior of the bag. It is suggested that this
extension supplies a crucial link to overcome the unsatisfactory existing
mismatch between multiskyrmion configurations and nuclear structure.Comment: 13 pages, 15 figure
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