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.

B.R.S. renormalisation of some on-shell closed algebras of symmetry transformations : N=2 and 4 supersymmetric non-linear sigma models

We analyse with the algebraic, regularisation independant, cohomological B.R.S. methods, the renormalisability of torsionless N=2 and N= 4 supersymmetric non-linear \si models built on K\"ahler spaces. Surprisingly enough with respect to the common wisdom, in the case of N=2 supersymmetry, we obtain an anomaly candidate, at least in the compact K\"ahler Ricci-flat case. If its coefficient does differ from zero, such anomaly would imply the breaking of global N=2 supersymmetry and get into trouble some schemes of superstring compactification as such non-linear \si models offer candidates for the superstring vacuum state. In the compact homogeneous K\"ahler case, as expected, the anomaly candidate disappears. The same phenomena occurs when one enforces N=4 supersymmetry : in that case, we obtain the first rigorous proof of the expected all-orders renormalisability -`` in the space of metrics"- of the corresponding non-linear \si models. PAR/LPTHE/94-11Comment: 22 pages, latex, PAR/LPTHE/94-1

‘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