32,694 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.
Diffuse interstellar bands in fullerene planetary nebulae: the fullerenes - diffuse interstellar bands connection
We present high-resolution (R~15000) VLT/UVES optical spectra of two
planetary nebulae (PNe; Tc 1 and M 1-20) where C60 (and C70) fullerenes have
already been found. These spectra are of high-quality (S/N > 300) for PN Tc 1,
which permits us to search for the expected electronic transitions of neutral
C60 and diffuse interstellar bands (DIBs). Surprisingly, we report the
non-detection of the most intense optical bands of C60 in Tc 1, although this
could be explained by the low C60 column density estimated from the C60
infrared bands if the C60 emission peaks far away from the central star. The
strongest and most common DIBs in both fullerene PNe are normal for their
reddening. Interestingly, the very broad 4428 A DIB and the weaker 6309 A DIB
are found to be unusually intense in Tc 1. We also report the detection of a
new broad (FWHM~5 A) unidentified band at ~6525 A. We propose that the 4428 A
DIB (probably also the 6309 A DIB and the new 6525 A band) may be related to
the presence of larger fullerenes (e.g., C80, C240, C320, and C540) and
buckyonions (multishell fullerenes such as C60@C240 and C60@C240@C540) in the
circumstellar envelope of Tc 1.Comment: Accepted for publication in Astronomy & Astrophysics Letters (6
pages, 4 figures, and 1 Table
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
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