5,272 research outputs found
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.
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
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
Screening effects in Relativistic Models of Dense Matter at Finite Temperature
We investigate screening effects of the medium on the potential interaction
between two static 'charges' for different models of dense plasmas in the
one-boson exchange approximation. The potential can exhibit an oscillatory
behavior, which is related to the analytic structure of the corresponding boson
propagators in the complex -plane. We have first revisited the one-pion
exchange in a nuclear medium. In addition to Friedel oscillations, which are
associated to branch cuts in the -plane, there appears another oscillatory
component, which arises from a pole on the pion propagator. This pole is
located appart from the axes, giving rise to an oscillating Yukawa-like
potential. Therefore, we call this phenomenon 'Yukawa oscillations'. This
phenomenon does not appear in the Debye component of the QED screened
potential, even if the coupling constant is artificially increased. We have
also studied a model of QCD quark-gluon plasma. In this case, the one-gluon
propagator also shows this kind of poles. At high densities and/or
temperatures, where one expects perturbative QCD to be valid, the pole shifts
towards large momenta.Comment: Revtex. 9 pages, 9 figure
Electrostatic internal energy using the method of images
For several configurations of charges in the presence of conductors, the
method of images permits us to obtain some observables associated with such a
configuration by replacing the conductors with some image charges. However,
simple inspection shows that the potential energy associated with both systems
does not coincide. Nevertheless, it can be shown that for a system of a
grounded or neutral conductor and a distribution of charges outside, the
external potential energy associated with the real charge distribution embedded
in the field generated by the set of image charges is twice the value of the
internal potential energy associated with the original system. This assertion
is valid for any size and shape of the conductor, and regardless of the
configuration of images required. In addition, even in the case in which the
conductor is not grounded nor neutral, it is still possible to calculate the
internal potential energy of the original configuration through the method of
images. These results show that the method of images could also be useful for
calculations of the internal potential energy of the original system.Comment: 5 pages, 3 figures. New discussions added. Minor change
Solutions of the dispersion equation in the region of overlapping of zero-sound and particle-hole modes
In this paper the solutions of the zero-sound dispersion equation in the
random phase approximation (RPA) are considered. The calculation of the damped
zero-sound modes \omega_s(k) (complex frequency of excitation) in the nuclear
matter is presented. The method is based on the analytical structure of the
polarization operators \Pi(\omega,k). The solutions of two dispersion equations
with \Pi(\omega,k) and with Re(\Pi(\omega,k)) are compared. It is shown that in
the first case we obtain one-valued smooth solutions without "thumb-like"
forms. Considering the giant resonances in the nuclei as zero-sound excitations
we compare the experimental energy and escape width of the giant dipole
resonance (GDR) in the nucleus A with \omega_s(k) taken at a definite wave
vector k=k_A.Comment: 14 pages, 5 figures; revised versio
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