251 research outputs found

### Inclusion of Diffraction Effects in the Gutzwiller Trace Formula

The Gutzwiller trace formula is extended to include diffraction effects. The
new trace formula involves periodic rays which have non-geometrical segments as
a result of diffraction on the surfaces and edges of the scatter.Comment: 4 pages, LaTeX, 1 ps figur

### Wave Chaos in Elastodynamic Cavity Scattering

The exact elastodynamic scattering theory is constructed to describe the
spectral properties of two- and more-cylindrical cavity systems, and compared
to an elastodynamic generalization of the semi-classical Gutzwiller unstable
periodic orbits formulas. In contrast to quantum mechanics, complex periodic
orbits associated with the surface Rayleigh waves dominate the low-frequency
spectrum, and already the two-cavity system displays chaotic features.Comment: 7 pages, 5 eps figures, latex (with epl.cls

### Model-independent approach to eta -> pi+ pi- gamma and eta' -> pi+ pi- gamma

We present a new, model-independent method to analyze radiative decays of
mesons to a vector, isovector pair of pions of invariant mass square below the
first significant pion-pion threshold in the vector channel. It is based on a
combination of chiral perturbation theory and dispersion theory. This allows
for a controlled inclusion of resonance physics without the necessity to
involve vector meson dominance explicitly. As an example, the method is applied
to an analysis of the reactions eta -> pi+ pi- gamma and eta'->pi+ pi- gamma.Comment: 16 pages, 4 figure

### Unexpected goings-on in the structure of a neutron star crust

We present a brief account of two phenomena taking place in a neutron star
crust: the Fermionic Casimir effect and the major density depletion of the
cores of the superfluid neutron vortices.Comment: 6 pages, invited talk presented by AB at Tours 2003 Symposium on
Nuclear Physics, August 26-29,Tours, Franc

### Deriving the quark condensate within a finite Fermi system from the generating functional of chiral perturbation theory

The generating functional of heavy baryon chiral perturbation theory at order {\cal O}(Q^2) in the mean field approximation (with a pseudoscalar source coupling which is consistent with the PCAC-Ward identities on the current quark level) has been exploited to derive Migdal's in--medium pion propagator. It is shown that the prediction for the density dependence of the quark condensate obtained on the composite hadron level by embedding PCAC within the framework of Migdal's approach to finite Fermi systems is identical to that resulting from QCD

### In-Medium Pion Properties from Chiral Perturbation Theory

Two--point functions related to the pion weak decay constant $f_\pi$ are calculated from the generating functional of chiral perturbation theory in the mean field approximation and the heavy--baryon limit. The aim is to demonstrate that Lorentz invariance is violated in the presence of background matter. This fact manifests itself in the splitting of both $f_\pi$ and the pion mass into uncorrelated time-- and space--like parts. We emphasize the different in--medium renormalizations of the correlation functions, show the inequivalence between the in--medium values of $f_\pi$ deduced from Walecka--type models, on the one hand, and QCD sum rules, on the other hand, and elaborate on the importance for some nuclear physics observables

### Neutron-Proton Mass Difference in Nuclear Matter and in Finite Nuclei and the Nolen-Schiffer Anomaly

The neutron-proton mass difference in (isospin asymmetric) nuclear matter and
finite nuclei is studied in the framework of a medium-modified Skyrme model.
The proposed effective Lagrangian incorporates both the medium influence of the
surrounding nuclear environment on the single nucleon properties and an
explicit isospin-breaking effect in the mesonic sector. Energy-dependent
charged and neutral pion optical potentials in the s- and p-wave channels are
included as well. The present approach predicts that the neutron-proton mass
difference is mainly dictated by its strong part and that it markedly decreases
in neutron matter. Furthermore, the possible interplay between the effective
nucleon mass in finite nuclei and the Nolen-Schiffer anomaly is discussed. In
particular, we find that a correct description of the properties of mirror
nuclei leads to a stringent restriction of possible modifications of the
nucleon's effective mass in nuclei.Comment: 10 pages, 8 figures, presentation at the 19th Int. IUPAP Conf. on
Few-Body Problems in Physics (Aug.31-Sep.5, 2009, Univ.of Bonn, Germany

### Quantum energies with worldline numerics

We present new results for Casimir forces between rigid bodies which impose
Dirichlet boundary conditions on a fluctuating scalar field. As a universal
computational tool, we employ worldline numerics which builds on a combination
of the string-inspired worldline approach with Monte-Carlo techniques.
Worldline numerics is not only particularly powerful for inhomogeneous
background configurations such as involved Casimir geometries, it also provides
for an intuitive picture of quantum-fluctuation-induced phenomena. Results for
the Casimir geometries of a sphere above a plate and a new perpendicular-plates
configuration are presented.Comment: 8 pages, 2 figures, Submitted to the Proceedings of the Seventh
Workshop QFEXT'05 (Barcelona, September 5-9, 2005), Refs updated, version to
appear in JPhys

### Instantons As Unitary Spin Maker

The instanton-induced determinantal 't Hooft interaction is built into a three-flavor linear sigma model which is considered in the OZI-rule-respecting basis. The mixing of the strange and non-strange quarkonia, which is due to the presence of instantons in combination with the spontaneous breaking of chiral symmetry, is shown to be ideal thus leading to the formation of an octet-flavor state. We study the impact of 't Hooft's interaction on the eta NN coupling finding the usual SU(3) results for this coupling, however, with possible generalizations to non-ideal mixing angles and different values of the meson decay constants in the strange and non-strange sectors, respectively

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