54 research outputs found
Symmetry conserving non-perturbative s-wave renormalization of the pion in hot and baryon dense medium
A non-perturbative s-wave renormalization of the pion in a hot and baryon
rich medium is presented. This approach proceeds via a mapping of the canonical
pion into the axial Noether's charge. The mapping was made dynamical in the
Hartree-Fock-Bogoliubov random phase approximation (HFB-RPA). It is shown that
this approach, while order mixing, is still symmetry conserving both in the
baryon free and baryon rich sectors, at zero as well as finite temperature. The
systematic character of this approach is emphasized and it is particularly
argued that it may constitute an interesting alternative for the
non-perturbative assessment of the nuclear matter saturation properties.Comment: Latex, 22 pages, 3 figure
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
Random phase approximation and its extension for the quantum O(2) anharmonic oscillator
We apply the random phase approximation (RPA) and its extension called
renormalized RPA to the quantum anharmonic oscillator with an O(2) symmetry. We
first obtain the equation for the RPA frequencies in the standard and in the
renormalized RPA approximations using the equation of motion method. In the
case where the ground state has a broken symmetry, we check the existence of a
zero frequency in the standard and in the renormalized RPA approximations. Then
we use a time-dependent approach where the standard RPA frequencies are
obtained as small oscillations around the static solution in the time-dependent
Hartree-Bogoliubov equation. We draw a parallel between the two approaches.Comment: 26 pages, Latex file, no figur
In-Medium Properties of Hadrons
A diverse experimental program for the study of the photoproduction of mesons
off nuclei has been carried out - and is still running - at the Mainz MAMI and
Bonn ELSA electron accelerators with the TAPS, Crystal Barrel, and Crystal Ball
calorimeters. It is motivated as a detailed study of the in-medium properties
of hadrons and the meson - nucleus interactions. Typical examples for the
in-medium behavior of vector mesons (), scalar mesons (), and
nucleon resonances (P(1232), S(1535), D(1520)) are
discussed. Special attention is paid to meson - nucleus final state
interactions.Comment: Proceedings of the Meson2006 IX Int. Workshop on Production,
Properties and Interaction of Mesons, Cracow, Poland 09 - 14 June, 2006, to
be published in Int. J. Mod. Phys.
A Non-Perturbative Treatment of the Pion in the Linear Sigma-Model
Using a non-perturbative method based on the selfconsistent Quasi-particle
Random-Phase Approximation (QRPA) we describe the properties of the pion in the
linear -model. It is found that the pion is massless in the chiral
limit, both at zero- and finite temperature, in accordance with Goldstone's
theorem.Comment: To appear in Nucl.Phys. A, 16 pages, 2 Postscript figure
Enhancement of Threshold Cross Sections by In-Medium Final State Interactions
We address the problem of pion production in low energy -nucleus
collisions. For the production mechanism we assume a simple model consisting of
a coherent sum of single pion exchange and the excitation---followed by the
decay into two pions and a nucleon---of the resonance. The
production amplitude is modified by the final state interaction between the
pions calculated using the chirally improved J\"ulich meson exchange model
including the polarization of the nuclear medium by the pions. The model
reproduces well the experimentally observed cross
sections, especially the enhancement with increasing of the
mass distribution in the threshold region.Comment: 5 pages RevTeX, 3-eps figure
S-Wave Pion-Pion Correlations in Dense Nuclear Matter
The s-wave correlated - strength distribution in cold nuclear
matter is investigated. The in-medium single pions are renormalized by means of
the usual p-wave couplings to nucleons and 's. Two groups of models for
the - interaction are studied. The first one uses phenomenological
models which reproduce the phase shifts but do not respect the soft-pion
theorems. With increasing density a strong accumulation of strength in the
subhreshold region is observed. Slightly above saturation density there even
occurs an instability with respect to s-wave - pair condensation.
These effects are strongly moderated or disappear altogether if constraints
from chiral symmetry are built into the - interaction.Comment: 22 pages, LATEX, 12 figures (not included, available from the
authors), KFA-IKP(TH)-1994-2
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