352 research outputs found
Thermodynamic consistency for nuclear matter calculations
We investigate the relation between the binding energy and the Fermi energy
and between different expressions for the pressure in cold nuclear matter. For
a self-consistent calculation based on a derivable matrix
approximation with off-shell propagators the thermodynamic relations are well
satisfied unlike for a matrix or a matrix approach using quasi-particle
propagators in the ladder diagrams
Screening Masses of Scalar and Pseudo-scalar Excitations in Quark-gluon Plasma
The quark-gluon plasma (QGP) excitations, corresponding to the scalar and
pseudoscalar meson quantum numbers, for different temperatures are calculated.
Analysis is performed in the Hard Thermal Loop (HTL) Approximation and leads to
a better understanding of the excitations of QGP in the deconfined phase and is
also of relevance for lattice studies
Feynman Diagrams and Rooted Maps
The Rooted Maps Theory, a branch of the Theory of Homology, is shown to be a
powerful tool for investigating the topological properties of Feynman diagrams,
related to the single particle propagator in the quantum many-body systems. The
numerical correspondence between the number of this class of Feynman diagrams
as a function of perturbative order and the number of rooted maps as a function
of the number of edges is studied. A graphical procedure to associate Feynman
diagrams and rooted maps is then stated. Finally, starting from rooted maps
principles, an original definition of the genus of a Feynman diagram, which
totally differs from the usual one, is given.Comment: 20 pages, 30 figures, 3 table
A Microscopic Energy- and Density-Dependent Effective Interaction and its Test by Nucleus-Nucleus Scattering
An effective nucleon-nucleon interaction calculated in nuclear matter from
the Bonn potential has been parametrized in terms of a local density- and
energy-dependent two-body interaction. This allows to calculate the real part
of the nucleus-nucleus scattering potential and to test this effective
interaction over a wide region of densities () produced
dynamically in scattering experiments. Comparing our calculations with
empirical potentials extracted from data on light and heavy ion scattering by
model-unrestricted analysis methods, we find quantitative agreement with the
exception of proton scattering. The failure in this case may be traced back to
the properties of the effective interaction at low densities, for which the
nuclear matter results are not reliable. The success of the interaction at high
overlap densities confirms the empirical evidence for a soft equation of state
for cold nuclear matter.Comment: 8 pages 3 Figures included, to appear in Phys. Lett.
Quantum mechanical ab-initio simulation of the electron screening effect in metal deuteride crystals
In antecedent experiments the electron screening energies of the d+d
reactions in metallic environments have been determined to be enhanced by an
order of magnitude in comparison to the case of gaseous deuterium targets. The
analytical models describing averaged material properties have not been able to
explain the experimental results so far. Therefore, a first effort has been
undertaken to simulate the dynamics of reacting deuterons in a metallic lattice
by means of an ab-initio Hartree-Fock calculation of the total electrostatic
force between the lattice and the successively approaching deuterons via path
integration. The calculations have been performed for Li and Ta, clearly
showing a migration of electrons from host metallic to the deuterium atoms.
However, in order to avoid more of the necessary simplifications in the model
the utilization of a massive parallel supercomputer would be required.Comment: 11 pages, 12 figures, svjour class. To be published in Eur. Phys. J.
Enhancement of the Deuteron-Fusion Reactions in Metals and its Experimental Implications
Recent measurements of the reaction d(d,p)t in metallic environments at very
low energies performed by different experimental groups point to an enhanced
electron screening effect. However, the resulting screening energies differ
strongly for divers host metals and different experiments. Here, we present new
experimental results and investigations of interfering processes in the
irradiated targets. These measurements inside metals set special challenges and
pitfalls which make them and the data analysis particularly error-prone. There
are multi-parameter collateral effects which are crucial for the correct
interpretation of the observed experimental yields. They mainly originate from
target surface contaminations due to residual gases in the vacuum as well as
from inhomogeneities and instabilities in the deuteron density distribution in
the targets. In order to address these problems an improved differential
analysis method beyond the standard procedures has been implemented. Profound
scrutiny of the other experiments demonstrates that the observed unusual
changes in the reaction yields are mainly due to deuteron density dynamics
simulating the alleged screening energy values. The experimental results are
compared with different theoretical models of the electron screening in metals.
The Debye-H\"{u}ckel model that has been previously proposed to explain the
influence of the electron screening on both nuclear reactions and radioactive
decays could be clearly excluded.Comment: 22 pages, 12 figures, REVTeX4, 2-column format. Submitted to Phys.
Rev. C; accepte
Collective Modes in a Slab of Interacting Nuclear Matter: The effects of finite range interactions
We consider a slab of nuclear matter and investigate the collective
excitations, which develop in the response function of the system. We introduce
a finite-range realistic interaction among the nucleons, which reproduces the
full G-matrix by a linear combination of gaussian potentials in the various
spin-isospin channels. We then analyze the collective modes of the slab in the
S=T=1 channel: for moderate momenta hard and soft zero-sound modes are found,
which exhaust most of the excitation strength. At variance with the results
obtained with a zero range force, new "massive" excitations are found for the
vector-isovector channel .Comment: 14 pages, TeX, 5 figures (separate uuencoded and tar-compressed
postscript files), Torino preprint DFTT 6/9
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