627 research outputs found
Quartetting Wave Function Approach to Ne: Shell Model and Local Density Approximation
We investigate -like correlations in Ne. A quartet of nucleons
(different spin/isospin) is moving in a mean field produced by the O
core nucleus. Improving the Thomas-Fermi model (local density approach), a
shell model is considered for the core nucleus. The effective potential of the
-like quartet and the wave function for the center-of-mass (c.o.m.)
motion are calculated and compared with other approaches.Comment: 10 pages, 7 figures. arXiv admin note: substantial text overlap with
arXiv:1707.0451
Correlations and Clustering in Dilute Matter
Nuclear systems are treated within a quantum statistical approach.
Correlations and cluster formation are relevant for the properties of warm
dense matter, but the description is challenging and different approximations
are discussed. The equation of state, the composition, Bose condensation of
bound fermions, the disappearance of bound states at increasing density because
of Pauli blocking are of relevance for different applications in astrophysics,
heavy ion collisions, and nuclear structure.Comment: 22 pages, 7 figures, contribution to the special-topics volume on
nuclear correlations and cluster physics, edited by W. U. Schr\"ode
Entropy production in open quantum systems: exactly solvable qubit models
We present analytical results for the time-dependent information entropy in
exactly solvable two-state (qubit) models. The first model describes dephasing
(decoherence) in a qubit coupled to a bath of harmonic oscillators. The entropy
production for this model in the regimes of "complete" and "incomplete"
decoherence is discussed. As another example, we consider the damped
Jaynes-Cummings model describing a spontaneous decay of a two-level system into
the field vacuum. It is shown that, for all strengths of coupling, the open
system passes through the mixed state with the maximum information entropy.Comment: 9 pages, 3 figure
Quasiparticle light elements and quantum condensates in nuclear matter
Nuclei in dense matter are influenced by the medium. In the cluster mean
field approximation, an effective Schr\"odinger equation for the -particle
cluster is obtained accounting for the effects of the surrounding medium, such
as self-energy and Pauli blocking. Similar to the single-baryon states (free
neutrons and protons), the light elements (, internal quantum
state ) are treated as quasiparticles with energies that depend on the center of mass momentum , the temperature
, and the total densities of neutrons and protons, respectively.
We consider the composition and thermodynamic properties of nuclear matter at
low densities. At low temperatures, quartetting is expected to occur.
Consequences for different physical properties of nuclear matter and finite
nuclei are discussed.Comment: 5 pages, 1 figure, 2 table
Light clusters in nuclear matter: Excluded volume versus quantum many-body approaches
The formation of clusters in nuclear matter is investigated, which occurs
e.g. in low energy heavy ion collisions or core-collapse supernovae. In
astrophysical applications, the excluded volume concept is commonly used for
the description of light clusters. Here we compare a phenomenological excluded
volume approach to two quantum many-body models, the quantum statistical model
and the generalized relativistic mean field model. All three models contain
bound states of nuclei with mass number A <= 4. It is explored to which extent
the complex medium effects can be mimicked by the simpler excluded volume
model, regarding the chemical composition and thermodynamic variables.
Furthermore, the role of heavy nuclei and excited states is investigated by use
of the excluded volume model. At temperatures of a few MeV the excluded volume
model gives a poor description of the medium effects on the light clusters, but
there the composition is actually dominated by heavy nuclei. At larger
temperatures there is a rather good agreement, whereas some smaller differences
and model dependencies remain.Comment: 12 pages, 6 figures, published version, minor change
Light nuclei quasiparticle energy shift in hot and dense nuclear matter
Nuclei in dense matter are influenced by the medium. In the cluster mean
field approximation, an effective Schr\"odinger equation for the -particle
cluster is obtained accounting for the effects of the correlated medium such as
self-energy, Pauli blocking and Bose enhancement. Similar to the single-baryon
states (free neutrons and protons), the light elements (,
internal quantum state ) are treated as quasiparticles with energies
. These energies depend on the center of mass
momentum , as well as temperature and the total densities
of neutrons and protons, respectively. No equilibrium is considered so
that (or the corresponding chemical potentials ) are
fixed independently.
For the single nucleon quasiparticle energy shift, different approximate
expressions such as Skyrme or relativistic mean field approaches are well
known. Treating the -particle problem in appropriate approximations, results
for the cluster quasiparticle shifts are given. Properties of dense nuclear
matter at moderate temperatures in the subsaturation density region considered
here are influenced by the composition. This in turn is determined by the
cluster quasiparticle energies, in particular the formation of clusters at low
densities when the temperature decreases, and their dissolution due to Pauli
blocking as the density increases. Our finite-temperature Green function
approach covers different limiting cases: The low-density region where the
model of nuclear statistical equilibrium and virial expansions can be applied,
and the saturation density region where a mean field approach is possible
Interpolation formula for the electrical conductivity of nonideal plasmas
On the basis of a quantum-statistical approach to the electrical conductivity
of nonideal plasmas we derive analytical results in the classical low-density
regime, in the degenerate Born limit, and for the contribution of the
Debye-Onsager relaxation effect. These explicit results are used to construct
an improved interpolation formula of the electrical conductivity valid in a
wide range of temperature and density which allows to compare with available
experimental data of nonideal plasmas.Comment: 7 pages, 1 tabl
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