Cohomogeneity-one Einstein-Weyl structures : a local approach

We analyse in a systematic way the (non-)compact n-dimensional Einstein Weyl spaces equipped with a cohomogeneity-one metric. With no compactness hypothesis, we prove that, as soon as the (n-1)-dimensional space is an homogeneous reductive Riemannian space with an unimodular group of left-acting isometries G 1)a non-exact Einstein-Weyl stucture may exist only if the (n-1)-dimensional homogeneous space G/H contains a non trivial subgroup H' that commutes with the isotropy subgroup H, 2) the extra isometry due to this Killing vector corresponds to the right-action of one of the generators of the algebra of the subgroup H'. We also prove that the subclass with a one-dimensional subgroup H' corresponds to n-dimensional Riemannian locally conformally K\"ahler metrics, the (n-2)-dimensional space G/(HxH') being an arbitrary compact symmetric K\"ahler coset space.Comment: 36 pages, Latex file, corrections in some definitions and terminology, no change in results, final version to appear in `` Journal of Geometry and Physics

‘Time’ in tourism: ‘individual time’ and ‘social time’

The author does a review of the research into tourist activity and concludes that the particular character of tourist behaviour is reflected best in the study of time budgets. He proposes Max Weber's ideal-type method to be used in the analysis. In the conclusions to the article the author presents typical examples of qualitative time (recreation, holidays, tourism)

Lorentz and CPT violations in QED : a short comment on recent controversies

We rediscuss the recent controversy on a possible Chern-Simons like term generated through radiative corrections in QED with a CPT violating term. We emphasize the fact that any absence of an {\sl a priori} divergence should be explained by some symmetry or some non-renormalisation theorem : otherwise, no prediction can be made on the corresponding quantity.Comment: 7 pages, LaTex file, 2 references adde

Regularisation : many recipes, but a unique principle : Ward identities and Normalisation conditions. The case of CPT violation in QED

We analyse the recent controversy on a possible Chern-Simons like term generated through radiative corrections in QED with a CPT violating term : we prove that, if the theory is correctly defined through Ward identities and normalisation conditions, no Chern-Simons term appears, without any ambiguity. This is related to the fact that such a term is a kind of minor modification of the gauge fixing term, and then no renormalised. The past year literature on that subject is discussed, and we insist on the fact that any absence of an {\sl a priori} divergence should be explained by some symmetry or some non-renormalisation theorem.Comment: 14 pages, Latex fil

Fission modes of 256Fm and 258Fm in a microscopic approach

A static microscopic study of potential-energy surfaces within the Skyrme-Hartree-Fock-plus-BCS model is carried out for the 256Fm and 258Fm isotopes with the goal of deducing some properties of spontaneous fission. The calculated fission modes are found to be in agreement with the experimentaly observed asymmetric-to-symmetric transition in the fragment-mass distributions and with the high- and low-total-kinetic-energy modes experimentally observed in 258Fm. Most of the results are similar to those obtained in macroscopic-microscopic models as well as in recent Hartree-Fock-Bogolyubov calculations with the Gogny interaction, with a few differences in their interpretations. In particular an alternative explanation is proposed for the low-energy fission mode of 258Fm.Comment: 14 pages, 11 figures, 3 tables, submitted to Phys. Rev.