One-loop finite temperature effective action of QED in the worldline approach

The one-loop finite temperature effective potential of QED in an external electromagnetic field is obtained using the worldline method. The general structure of the temperature dependent part of the effective action in an arbitrary external inhomogeneous magnetic field is established. The two-derivative effective action of spinor and scalar QED in a static magnetic background at $T\neq 0$ is derived.Comment: REVTeX, 5 pages. Minor corrections. Final version published in Phys. Lett.

Calculation of Heat-Kernel Coefficients and Usage of Computer Algebra

The calculation of heat-kernel coefficients with the classical DeWitt algorithm has been discussed. We present the explicit form of the coefficients up to $h_5$ in the general case and up to $h_7^{min}$ for the minimal parts. The results are compared with the expressions in other papers. A method to optimize the usage of memory for working with large expressions on universal computer algebra systems has been proposed.Comment: 12 pages, LaTeX, no figures. Extended version of contribution to AIHENP'95, Pisa, April 3-8, 199

17-jähriger Mann mit akuten Bauchschmerzen, Hämatochezie und Exanthem

Zusammenfassung: Ein 17-jähriger Patient stellte sich mit kolikartigen abdominellen Schmerzen und Diarrhö vor. Als weitere Symptome traten Petechien, Arthralgien und eine Hämatochezie auf. Sonographisch bestand eine auffällige Ileozökalregion. Endoskopisch fand sich eine Ileitis terminalis, und histologisch zeigte sich hier eine leukozytoklastische Vaskulitis mit IgA-Ablagerungen. Die Kasuistik zeigt exemplarisch die mehrzeitige klinische Manifestation der Purpura Schönlein-Henoch und deren Verlau

Pristine CNO abundances from Magellanic Cloud B stars II. Fast rotators in the LMC cluster NGC 2004

We present spectroscopic abundance analyses of three main-sequence B stars in the young Large Magellanic Cloud cluster NGC 2004. All three targets have projected rotational velocities around 130 km/s. Techniques are presented that allow the derivation of stellar parameters and chemical abundances in spite of these high v sin i values. Together with previous analyses of stars in this cluster, we find no evidence among the main-sequence stars for effects due to rotational mixing up to v sin i around 130 km/s. Unless the equatorial rotational velocities are significantly larger than the v sin i values, this finding is probably in line with theoretical expectations. NGC 2004/B30, a star of uncertain evolutionary status located in the Blue Hertzsprung Gap, clearly shows signs of mixing in its atmosphere. To verify the effects due to rotational mixing will therefore require homogeneous analysis of statistically significant samples of low-metallicity main-sequence B stars over a wide range of rotational velocities.Comment: 12 pages, 5 figures, 2 tables; accepted for publication in ApJ (vol. 633, p. 899

Diagrams for heat kernel expansions

A diagramatic heat kernel expansion technique is presented. The method is especially well suited to the small-derivative expansion of the heat kernel, but it can also be used to reproduce the results obtained by the approach known as covariant perturbation theory. The new technique gives an expansion for the heat kernel at coincident points. It can also be used to obtain the derivative of the heat kernel and this is useful for evaluating the expectation values of the stress-energy tensor.Comment: 17 pages, 4 figures, ReVTe

Vacuum polarization tensor in inhomogeneous magnetic fields

We develop worldline numerical methods, which combine string-inspired with Monte-Carlo techniques, for the computation of the vacuum polarization tensor in inhomogeneous background fields for scalar QED. The algorithm satisfies the Ward identity exactly and operates on the level of renormalized quantities. We use the algorithm to study for the first time light propagation in a spatially varying magnetic field. Whereas a local derivative expansion applies to the limit of small variations compared to the Compton wavelength, the case of a strongly varying field can be approximated by a derivative expansion for the averaged field. For rapidly varying fields, the vacuum-magnetic refractive indices can exhibit a non-monotonic dependence on the local field strength. This behavior can provide a natural limit on the self-focussing property of the quantum vacuum.Comment: 12 pages, 9 figure