111 research outputs found
Screening Effects on Pairing in Neutron Matter
The superfluidity of neutron matter is studied in the framework of
the generalized Gorkov equation. The vertex corrections to the pairing
interaction and the self-energy corrections are introduced and approximated on
the same footing in the gap equation. A suppression of the pairing gap by more
than 50% with respect to the BCS prediction is found, which deeply changes the
scenario for the dynamical and thermal evolution of neutron stars.Comment: 5 pages, 5 figres, RevTeX4 styl
Solution of the microscopic gap equation for a slab of nuclear matter with the Paris NN-potential
The gap equation in the -channel is solved for a nuclear slab with the
separable form of the Paris potential. The gap equation is considered in the
model space in terms of the effective pairing interaction which is found in the
complementary subspace. The absolute value of the gap turned out to be
very sensitive to the cutoff in the momentum space in the equation
for the effective interaction. It is necessary to take to guarantee 1% accuracy for . The gap equation itself is
solved directly, without any additional approximations. The solution reveals
the surface enhancement of the gap which was earlier found with an
approximate consideration. A strong surface-volume interplay was found also
implying a kind of the proximity effect. The diagonal matrix elements of
turned out to be rather close to the empirical values for heavy atomic
nuclei.Comment: 17 pages, 12 figure
In medium T matrix for neutron matter
We calculate the equation of state of pure neutron matter, comparing the
G-matrix calculation with the in-medium T-matrix result. At low densities, we
obtain similar energies per nucleon, however some differences appear at higher
densities. We use the self-consistent spectral functions from the T-matrix
approach to calculate the 1S0 superfluid gap including self-energy effects. We
find a reduction of the superfluid gap by 30%
1S0 Proton and Neutron Superfluidity in beta-stable Neutron Star Matter
We investigate the effect of a microscopic three-body force on the proton and
neutron superfluidity in the channel in -stable neutron star
matter. It is found that the three-body force has only a small effect on the
neutron pairing gap, but it suppresses strongly the proton
superfluidity in -stable neutron star matter.Comment: 12 pages, 2 figure
In-Medium Properties of Hadrons - Observables II
In this review we discuss the observable consequences of in-medium changes of
hadronic properties in reactions with elementary probes, and in particular
photons, on nuclei. After an outline of the theoretical method used we focus on
a discussion of actual observables in photonuclear reactions; we discuss in
detail - and vector-meson production. We show that the
photoproduction data can be well described by final state interactions of the
pions produced whereas the semi-charged channel exhibits a major
discrepancy with theory. For production on nuclei in the TAPS/CB@ELSA
experiment we analyse the decay channel, and illustrate the
strength of the method by simulating experimental acceptance problems.
Completely free of final state interactions is dilepton production in the few
GeV range. We show that the sensitivity of this decay channel to changes of
hadronic properties in medium in photonuclear reactions on nuclei is as large
as in ultrarelativistic heavy ion collisions and make predictions for the
on-going G7 experiment at JLAB. Finally we discuss that hadron production in
nuclei at 10 -- 20 GeV photon energies can give important information on the
hadronization process, and in particular on the time-scales involved. We show
here detailed calculations for the low-energy (12 GeV) run at HERMES and
predictions for planned experiments at JLAB.Comment: Invited Talk by U. Mosel, Proceedings of the Int. School on Nuclear
Physics, 26th Course, "Lepton scattering and the structure of hadrons and
nuclei", Erice (Sicily), September 16th-24th, 2004, short piece of text adde
Nucleon deformation in finite nuclei
The deformation of a nucleon embedded in various finite nuclei is considered
by taking into account the distortion of the chiral profile functions under the
action of an external field representing the nuclear density. The baryon charge
distribution of the nucleon inside light, medium-heavy and heavy nuclei is
discussed. The mass of the nucleon decreases as it is placed deeper inside the
nucleus and reaches its minimum at the center of the nucleus. We discuss the
quantization of non-spherical solitons and its consequences for the mass
splitting of the delta states. We show that bound nucleons acquire an intrinsic
quadrupole moment due to the deformation effects. These effects are maximal for
densities of nuclei about \rho(R)\sim 0.3...0.35 \rho(0). We also point out
that scale changes of the electromagnetic radii can not simply be described by
an overall swelling factor.Comment: 29 pp, REVTeX, 8 figures, more detailed discussion on quantization
and intrinsic quadrupole moments, references adde
Thermodynamics of - condensate in asymmetric nuclear matter
We study the neutron-proton pairing in nuclear matter as a function of
isospin asymmetry at finite temperatures and the saturation density using
realistic nuclear forces and Brueckner-renormalized single particle spectra.
Our computation of the thermodynamic quantities shows that while the difference
of the entropies of the superconducting and normal phases anomalously changes
its sign as a function of temperature for arbitrary asymmetry, the grand
canonical potential does not; the superconducting state is found to be stable
in the whole temperature-asymmetry plane. The pairing gap completely disappears
for density-asymmetries exceeding .Comment: 7 pages, including 3 figures, uses revte
In-medium Properties of Hadrons -- Observables
We first briefly review the theoretical basis for calculations of changes of
hadronic properties in dense nuclear matter. These changes have usually been
investigated by means of relativistic heavy-ion reactions. Here we discuss that
observable consequences of such changes can also be seen in more elementary
reactions on nuclei. Particular emphasis is put on a discussion of actual
observables in photonuclear reactions; we discuss in detail - and
vector-meson production. We show that photoproduction of 's can yield
essential information on in-medium properties of the resonance
while the meson properties will probably not be accessible through the
decay channel. However, for mesons the decay
channel, due to its reduced final state interaction, looks more promising in
this respect. Completely free of final state interactions is dilepton
production in the few GeV range. We show that the sensitivity of this decay
channel to changes of hadronic properties in medium in photonuclear reactions
on nuclei is as large as in ultrarelativistic heavy ion collisions. Finally we
discuss that hadron production in nuclei at 10 -- 20 GeV photon energies can
give important information on the hadronization process.Comment: Invited Lecture by U. Mosel at Erice International School on Nuclear
Physics 200
In medium T-matrix for superfluid nuclear matter
We study a generalized ladder resummation in the superfluid phase of the
nuclear matter. The approach is based on a conserving generalization of the
usual T-matrix approximation including also anomalous self-energies and
propagators. The approximation here discussed is a generalization of the usual
mean-field BCS approach and of the in medium T-matrix approximation in the
normal phase. The numerical results in this work are obtained in the
quasi-particle approximation. Properties of the resulting self-energy,
superfluid gap and spectral functions are studied.Comment: 38 pages, 19 figures, Introduction rewritten, Refs. adde
The Two-Nucleon Potential from Chiral Lagrangians
Chiral symmetry is consistently implemented in the two-nucleon problem at
low-energy through the general effective chiral lagrangian. The potential is
obtained up to a certain order in chiral perturbation theory both in momentum
and coordinate space. Results of a fit to scattering phase shifts and bound
state data are presented, where satisfactory agreement is found for laboratory
energies up to about 100 Mev.Comment: Postscript file; figures available by reques
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