Asymptotically anomalous black hole configurations in gravitating nonlinear electrodynamics

We analyze the class of non-linear electrodynamics minimally coupled to gravitation supporting asymptotically flat \textit{non Schwarzschild-like} elementary solutions. The Lagrangian densities governing the dynamics of these models in flat space are defined and fully characterized as a subclass of the set of functions of the two standard field invariants, restricted by requirements of regularity, parity invariance and positivity of the energy, which are necessary conditions for the theories to be physically admissible. Such requirements allow for a complete characterization and classification of the geometrical structures of the elementary solutions for the corresponding gravity-coupled models. In particular, an immediate consequence of the requirement of positivity of the energy is the asymptotic flatness of gravitating elementary solutions for any admissible model. The present analysis, together with the (already published) one concerning the full class of admissible gravitating non-linear electrodynamics supporting asymptotically flat \textit{Schwarzschild-like} elementary solutions, completes and exhausts the study of the gravitating point-like charge problem for this kind of models.Comment: 12 pages, 6 figures, revtex4, added extra paragraph in conclusions, added some references, added other minor changes, to published in Phys.Rev.

Hyperon ordering in neutron star matter

We explore the possible formation of ordered phases in neutron star matter. In the framework of a quantum hadrodynamics model where neutrons, protons and Lambda hyperons interact via the exchange of mesons, we compare the energy of the usually assumed uniform, liquid phase, to that of a configuration in which di-lambda pairs immersed in an uniform nucleon fluid are localized on the nodes of a regular lattice. The confining potential is calculated self-consistently as resulting from the combined action of the nucleon fluid and the other hyperons, under the condition of beta equilibrium. We are able to obtain stable ordered phases for some reasonable sets of values of the model parameters. This could have important consequences on the structure and cooling of neutron stars.Comment: 6 pages, 2 figures. To appear in the proceedings of the 4th Catania Relativistic Ion Studies: Exotic Clustering (CRIS 2002), Catania, Italy, 10-14 Jun 200

Electrostatic spherically symmetric configurations in gravitating nonlinear electrodynamics

We perform a study of the gravitating electrostatic spherically symmetric (G-ESS) solutions of Einstein field equations minimally coupled to generalized non-linear abelian gauge models in three space dimensions. These models are defined by lagrangian densities which are general functions of the gauge field invariants, restricted by some physical conditions of admissibility. They include the class of non-linear electrodynamics supporting ESS non-topological soliton solutions in absence of gravity. We establish that the qualitative structure of the G-ESS solutions of admissible models is fully characterized by the asymptotic and central-field behaviours of their ESS solutions in flat space (or, equivalently, by the behaviour of the lagrangian densities in vacuum and on the point of the boundary of their domain of definition, where the second gauge invariant vanishes). The structure of these G-ESS configurations for admissible models supporting divergent-energy ESS solutions in flat space is qualitatively the same as in the Reissner-Nordstr\"om case. In contrast, the G-ESS configurations of the models supporting finite-energy ESS solutions in flat space exhibit new qualitative features, which are discussed in terms of the ADM mass, the charge and the soliton energy. Most of the results concerning well known models, such as the electrodynamics of Maxwell, Born-Infeld and the Euler-Heisenberg effective lagrangian of QED, minimally coupled to gravitation, are shown to be corollaries of general statements of this analysis.Comment: 11 pages, revtex4, 4 figures; added references; introduction, conclusions and several sections extended, 2 additional figures included, title change

Friedel Oscillations in Relativistic Nuclear Matter

We calculate the low-momentum N-N effective potential obtained in the OBE approximation, inside a nuclear plasma at finite temperature, as described by the relativistic $\sigma$-$\omega$ model. We analyze the screening effects on the attractive part of the potential in the intermediate range as density or temperature increase. In the long range the potential shows Friedel-like oscillations instead of the usual exponential damping. These oscillations arise from the sharp edge of the Fermi surface and should be encountered in any realistic model of nuclear matter.Comment: 11 pages in preprint format, typeset using REVTEX, 3 included figures in tar, compressed, uuencoded forma

Hyperonic crystallization in hadronic matter

Published in Hadrons, Nuclei and Applications, World Scientific, Singapore, Proc.of the Conference Bologna2000. Structure of the Nucleus at the Dawn of the Century, G. Bonsignori, M. Bruno, A. Ventura, D. Vretenar Editors, pag. 319.Comment: 4 pages, 2figure

Work and energy in inertial and non inertial reference frames

It is usual in introductory courses of mechanics to develop the work and energy formalism from Newton's laws. On the other hand, literature analyzes the way in which forces transform under a change of reference frame. Notwithstanding, no analogous study is done for the way in which work and energy transform under those changes of reference frames. We analyze the behavior of energy and work under such transformations and show explicitly the expected invariance of the formalism under Galilean transformations for one particle and a system of particles. The case of non inertial systems is also analyzed and the fictitious works are characterized. In particular, we show that the total fictitious work in the center of mass system vanishes even if the center of mass defines a non inertial frame. Finally, some subtleties that arise from the formalism are illustrated by examples.Comment: 4 pages, 2 figures. LaTeX2e. Part of the approach has been changed but results are unaltered. Version to appear im American Journal of Physic