1,636 research outputs found
Occupation numbers in Self Consistent RPA
A method is proposed which allows to calculate within the SCRPA theory the
occupation numbers via the single particle Green function. This scheme complies
with the Hugenholtz van Hove theorem. In an application to the Lipkin model it
is found that this prescription gives consistently better results than two
other commonly used approximations: lowest order boson expansion and the number
operator method.Comment: 25 pages, 10 figures, submitted to Nucl. Phys.
The Linear Sigma-Model in the 1/N-Expansion via Dynamical Boson Mappings and Applications to -Scattering
We present a non-perturbative method for the study of the O(N+1)-version of
the linear sigma-model. Using boson-mapping techniques, in close analogy to
those well-known for fermionic systems, we obtain a systematic 1/N-expansion
for the Hamiltonian which is symmetry-conserving order by order. The leading
order for the Hamiltonian is evaluated explicitly and we apply the method to
-scattering, in deriving the T-matrix to leading order.Comment: 28 pages, Latex, (with minor corrections to some misprints in the
appendix of the old version
Two-particle spatial correlations in superfluid nuclei
We discuss the effect of pairing on two-neutron space correlations in
deformed nuclei. The spatial correlations are described by the pairing tensor
in coordinate space calculated in the HFB approach. The calculations are done
using the D1S Gogny force. We show that the pairing tensor has a rather small
extension in the relative coordinate, a feature observed earlier in spherical
nuclei. It is pointed out that in deformed nuclei the coherence length
corresponding to the pairing tensor has a pattern similar to what we have found
previously in spherical nuclei, i.e., it is maximal in the interior of the
nucleus and then it is decreasing rather fast in the surface region where it
reaches a minimal value of about 2 fm. This minimal value of the coherence
length in the surface is essentially determined by the finite size properties
of single-particle states in the vicinity of the chemical potential and has
little to do with enhanced pairing correlations in the nuclear surface. It is
shown that in nuclei the coherence length is not a good indicator of the
intensity of pairing correlations. This feature is contrasted with the
situation in infinite matter.Comment: 14 pages, 17 figures, submitted to PR
Nuclear Pairing in the T=0 channel revisited
Recent published data on the isoscalar gap in symmetric nuclear matter using
the Paris force and the corresponding BHF single particle dispersion are
corrected leading to an extremely high proton-neutron gap of
MeV at . Arguments whether this value can be reduced due
to screening effects are discussed. A density dependent delta interaction with
cut off is adjusted so as to approximately reproduce the nuclear matter values
with the Paris force.Comment: 4 pages, 4 figure
Fission from saddle to exit : influence of curvature and compression energies
We investigate the influence of terms beyond the standard Liquid Drop Model on the slope of the fission valley. An important reduction of the slope is obtained when using values of the curvature energy calculated from effective forces currently in use, thus corroborating a recent microscopic calculation by Berger et al
Enhancing teacher education practice through professional learning conversations
The paper discusses the value of peer observation followed by professional learning conversations for the professional development of teacher educators. The authors analyse their shared learning experiences and articulate what challenged them in these experiences. They discuss the ways in which their perceptions of this process differed or were similar. The grounding of the experience in a context of trust and professional relationship was seen as an essential part of the learning process. The authors highlight the importance of the cognitive-emotional and personal-professional aspects of teacher educators' lives in supporting their learning through the combination of peer observation and ongoing professional learning conversations. © 2008 Association for Teacher Education in Europe
Boson-Fermion pairing in a Boson-Fermion environment
Propagation of a Boson-Fermion (B-F) pair in a B-F environment is considered.
The possibility of formation of stable strongly correlated B-F pairs, embedded
in the continuum, is pointed out. The new Fermi gas of correlated B-F pairs
shows a strongly modified Fermi surface. The interaction between like particles
is neglected in this exploratory study. Various physical situations where our
new pairing mechanism could be of importance are invoked.Comment: 8 pages, 8 figers, to be published in Phys. Rev.
Dynamics of a trapped Fermi gas in the BCS phase
We derive semiclassical transport equations for a trapped atomic Fermi gas in
the BCS phase at temperatures between zero and the superfluid transition
temperature. These equations interpolate between the two well-known limiting
cases of superfluid hydrodynamics at zero temperature and the Vlasov equation
at the critical one. The linearized version of these equations, valid for small
deviations from equilibrium, is worked out and applied to two simple examples
where analytical solutions can be found: a sound wave in a uniform medium and
the quadrupole excitation in a spherical harmonic trap. In spite of some
simplifying approximations, the main qualitative results of quantum mechanical
calculations are reproduced, which are the different frequencies of the
quadrupole mode at zero and the critical temperature and strong Landau damping
at intermediate temperatures. In addition we suggest a numerical method for
solving the semiclassical equations without further approximations.Comment: 15 pages, 4 figures; v2: discussion and references adde
Continued fraction approximation for the nuclear matter response function
We use a continued fraction approximation to calculate the RPA response
function of nuclear matter. The convergence of the approximation is assessed by
comparing with the numerically exact response function obtained with a typical
effective finite-range interaction used in nuclear physics. It is shown that
just the first order term of the expansion can give reliable results at
densities up to the saturation density value
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