Axial current matrix elements and pentaquark decay widths in chiral soliton models

Here I explain why in chiral soliton models the hadronic transition operator of the pentaquark decay cannot be identified from the axial current.Comment: seven pages, note on Delta resonance added, refs updated, version to be published in PR

Neutron star properties in the Thomas-Fermi model

The modern nucleon-nucleon interaction of Myers and Swiatecki, adjusted to the properties of finite nuclei, the parameters of the mass formula, and the behavior of the optical potential is used to calculate the properties of $\beta$--equilibrated neutron star matter, and to study the impact of this equation of state on the properties of (rapidly rotating) neutron stars and their cooling behavior. The results are in excellent agreement with the outcome of calculations performed for a broad collection of sophisticated nonrelativistic as well as relativistic models for the equation of state.Comment: 23 pages, LaTeX, 15 ps-figure

Quantum stabilization of a hedgehog type of cosmic string

Within a slightly simplified version of the electroweak standard model we investigate the stabilization of cosmic strings by fermion quantum fluctuations. Previous studies of quantum energies considered variants of the Nielsen-Olesen profile embedded in the electroweak gauge group and showed that configurations are favored for which the Higgs vacuum expectation value drops near the string core and the gauge field is suppressed. This work found that the strongest binding was obtained from strings that differ significantly from Nielsen-Olesen configurations, deforming essentially only the Higgs field in order to generate a strong attraction without inducing large gradients. Extending this analysis, we consider the leading quantum correction to the energy per unit length of a hedgehog type string, which, in contrast to the Nielsen-Olesen configuration, contains a pseudoscalar field. To employ the spectral method we develop the scattering and bound state problems for fermions in the background of a hedgehog string. Explicit occupation of bound state levels leads to strings that carry the quantum numbers of the bound fermions. We discuss the parameter space for which stable, hedgehog type cosmic strings emerge and reflect on phenomenological consequences of these findings.Comment: 34 page

Attractive Electromagnetic Casimir Stress on a Spherical Dielectric Shell

Based on calculations involving an idealized boundary condition, it has long been assumed that the stress on a spherical conducting shell is repulsive. We use the more realistic case of a Drude dielectric to show that the stress is attractive, matching the generic behavior of Casimir forces in electromagnetism. We trace the discrepancy between these two cases to interactions between the electromagnetic quantum fluctuations and the dielectric material.Comment: Five pages, one figure, pdflatex, matches version to be pusblished in Phys Lett

Quasi Periodic Oscillations in Low Mass X-Ray Binaries and Constraints on the Equation of State of Neutron Star Matter

Recently discovered quasi periodic oscillations in the X-ray brightness of low mass X-ray binaries are used to derive constraints on the mass of the neutron star component and the equation of state of neutron star matter. The observations are compared with models of rapidly rotating neutron stars which are calculated by means of an exact numerical method in full relativity. For the equations of state we select a broad collection of models representing different assumptions about the many-body structure and the complexity of the composition of super dense matter. The mass constraints differ from their values in the approximate treatment by \sim 10%. Under the assumption that the maximum frequency of the quasi periodic oscillations originates from the innermost stable orbit the mass of the neutron star is in the range: $M\sim 1.92-2.25 M_\odot$. Especially the quasi periodic oscillation in the Atoll-source 4U 1820-30 is only consistent with equations of state which are rather stiff at high densities which is explainable, so far, only with pure nucleonic/leptonic composition. This interpretation contradicts the hypothesis that the protoneutron star formed in SN 1987A collapsed to a black hole, since this would demand a maximum neutron star mass below $1.6 M_\odot$. The recently suggested identification of quasi periodic oscillations with frequencies around 10 Hz with the Lense-Thirring precession of the accretion disk is found to be inconsistent with the models studied in this work, unless it is assumed that the first overtone of the precession is observed.Comment: 12 pages including figures, to be published in MNRA

Spectral Methods for Coupled Channels with a Mass Gap

We develop a method to compute the vacuum polarization energy for coupled scalar fields with different masses scattering off a background potential in one space dimension. As an example we consider the vacuum polarization energy of a kink-like soliton built from two real scalar fields with different mass parameters.Comment: 14 pages, 5 figures, matches journal version, references added (surprisingly many