1,217 research outputs found
Supersymmetry of gravitational ground states
A class of black objects which are solutions of pure gravity with negative
cosmological constant are classified through the mapping between the Killing
spinors of the ground state and those of the transverse section. It is shown
that these geometries must have transverse sections of constant curvature for
spacetime dimensions d below seven. For d > 6, the transverse sections can also
be Euclidean Einstein manifolds. In even dimensions, spacetimes with transverse
section of nonconstant curvature exist only in d = 8 and 10. This
classification goes beyond standard supergravity and the eleven dimensional
case is analyzed. It is shown that if the transverse section has negative
scalar curvature, only extended objects can have a supersymmetric ground state.
In that case, some solutions are explicitly found whose ground state resembles
a wormhole.Comment: 16 pages, CECS style, minor correction
Higher Dimensional Gravity, Propagating Torsion and AdS Gauge Invariance
The most general theory of gravity in d-dimensions which leads to second
order field equations for the metric has [(d-1)/2] free parameters. It is shown
that requiring the theory to have the maximum possible number of degrees of
freedom, fixes these parameters in terms of the gravitational and the
cosmological constants. In odd dimensions, the Lagrangian is a Chern-Simons
form for the (A)dS or Poincare groups. In even dimensions, the action has a
Born-Infeld-like form. Torsion may occur explicitly in the Lagrangian in the
parity-odd sector and the torsional pieces respect local (A)dS symmetry for
d=4k-1 only. These torsional Lagrangians are related to the Chern-Pontryagin
characters for the (A)dS group. The additional coefficients in front of these
new terms in the Lagrangian are shown to be quantized.Comment: 10 pages, two columns, no figures, title changed in journal, final
version to appear in Class. Quant. Gra
Osteocondroma intra-raquideo con afectación neurológica
Se presenta el caso de un varón de 16 años con lumbalgia consecutiva a
traumatismo vertebral, sin hallazgo s radiológicos, que no mejoraba con tratamient o
conservador, y que a las 5 semanas desarrolló un cuadro de paraparesia e incontinencia
de esfínteres indicativo de afectación del cono medular. En el estudio mielográfico
se objetivó bloqueo completo a nivel de Ll. La tomografía axial mostró una imagen sugestiva
de osteocondroma intraraquídeo, que s e confirmó quirúrgicamente . Dos año s
tras la intervención, se logró la total recuperación neurológica. Se destaca la rareza de
la lesión, la dificultad diagnóstica, y la probable etiología traumática de la tumoración.A 16-year-old man with no improvement of low back pain after vertebral
trauma conservatively treated and without radiological findings is presented. Five weeks
after trauma, the patient developed paraparesia and fecal and urinary incontinence
indicating compression of the medullary conus. A complet e stop of the contrast at
Ll level wa s found in the myelographi c study. The CT-Scan showed an image suggesting
osteochondroma whic h wa s confirmed a r surgery. Complet e neurogical recover y
w a s achieved 2 year s after surgical treatment. The rare character of the lesion, the dificulty
for diagnosis and the probable traumatic etiology of this tumor is discussed
Black Hole Scan
Gravitation theories selected by requiring that they have a unique anti-de
Sitter vacuum with a fixed cosmological constant are studied. For a given
dimension d, the Lagrangians under consideration are labeled by an integer
k=1,2,...,[(d-1)/2]. Black holes for each d and k are found and are used to
rank these theories. A minimum possible size for a localized electrically
charged source is predicted in the whole set of theories, except General
Relativity. It is found that the thermodynamic behavior falls into two classes:
If d-2k=1, these solutions resemble the three dimensional black hole,
otherwise, their behavior is similar to the Schwarzschild-AdS_4 geometry.Comment: Two columns, revtex, 15 pages, 5 figures, minor typos corrected,
final version for Journa
Evaluation of salt tolerance of in vitro-grown grapevine rootstock varieties
The response of 11 grapevine rootstock varieties to increasing salt concentrations (0, 50, 85, 120, 155 mM NaCl) was studied under in vitro and growth chamber conditions. The effect of salinity on the mortality of explants was compared with that of plantlets grown under growth chamber conditions and with data in literature on rootstock resistance under field conditions. In addition, in vitro stem elongation bud number, and rooting ability were related to salinity. The rootstock varieties can be divided into sensitive (41 B, R.Lot, 110 R, 140 R and 161-49), moderately tolerant (13.5 and Ramsey) and tolerant (196-17, CH-1, CH-2 and Superior). Measurements of the water and nutrient contents of plantlets indicate that increasing salt concentrations decreased the hydration of aerial parts and roots of all plants; however, the decrease of hydration was smaller in salt tolerant varieties. Increasing salt concentrations significantly reduced the K content and, to a smaller extent, the P and Ca contents. With and without salt treatments the levels of K and P were lower in sensitive plants. Na and Cl accumulated to a higher extent in tolerant plants. The tolerance to NaCl of in vitro-grown rootstocks seems to be due to their capacity to accumulate salt, to increase K concentration in the tissue and to maintain a high water content. Our results indicate that salt tolerance of grapevine varieties may be tested under growth chamber conditions and using in vitro explants
Transgression forms and extensions of Chern-Simons gauge theories
A gauge invariant action principle, based on the idea of transgression forms,
is proposed. The action extends the Chern-Simons form by the addition of a
boundary term that makes the action gauge invariant (and not just
quasi-invariant). Interpreting the spacetime manifold as cobordant to another
one, the duplication of gauge fields in spacetime is avoided. The advantages of
this approach are particularly noticeable for the gravitation theory described
by a Chern-Simons lagrangian for the AdS group, in which case the action is
regularized and finite for black hole geometries in diverse situations. Black
hole thermodynamics is correctly reproduced using either a background field
approach or a background-independent setting, even in cases with asymptotically
nontrivial topologies. It is shown that the energy found from the thermodynamic
analysis agrees with the surface integral obtained by direct application of
Noether's theorem.Comment: 28 pages, no figures. Minor changes in the introduction, final
comments and reference
Metallicity evolution, metallicity gradients and gas fractions at z~3.4
We used near-infrared integral field spectroscopic observations from the
AMAZE and LSD programs to constrain the metallicity in a sample of 40 star
forming galaxies at 3<z<5 (most of which at z~3.4). We measure metallicities by
exploiting strong emission line diagnostics. We found that a significant
fraction of star-forming galaxies at z~3.4 deviate from the Fundamental
Metallicity Relation (FMR), with a metallicity up to a factor of ten lower than
expected according to the FMR. This deviation does not correlate with the
dynamical properties of the galaxy or with the presence of interactions. To
investigate the origin of the metallicity deviations in more detail, we also
infer information on the gas content, by inverting the Schmidt-Kennicutt
relation. In agreement with recent CO observational data, we found that, in
contrast with the steeply rising trend at 0<z<2, the gas fraction in massive
galaxies remains constant, with indication of a marginal decline, at 2<z<3.5.
When combined with the metallicity information, we infer that to explain both
the low metallicity and gas content in z~3.4 galaxies, both prominent outflows
and massive pristine gas inflows are needed. In ten galaxies we can also
spatially resolve the metallicity distribution. We found that the metallicity
generally anticorrelates with the distribution of star formation and with the
gas surface density. We discuss these findings in terms of pristine gas inflows
towards the center, and outflows of metal rich gas from the center toward the
external regions. (Abridged)Comment: Replaced to match the published versio
Kerr-Schild ansatz in Einstein-Gauss-Bonnet gravity: An exact vacuum solution in five dimensions
As is well-known, Kerr-Schild metrics linearize the Einstein tensor. We shall
see here that they also simplify the Gauss-Bonnet tensor, which turns out to be
only quadratic in the arbitrary Kerr-Schild function f when the seed metric is
maximally symmetric. This property allows us to give a simple analytical
expression for its trace, when the seed metric is a five dimensional maximally
symmetric spacetime in spheroidal coordinates with arbitrary parameters a and
b. We also write in a (fairly) simple form the full Einstein-Gauss-Bonnet
tensor (with a cosmological term) when the seed metric is flat and the
oblateness parameters are equal, a=b. Armed with these results we give in a
compact form the solution of the trace of the Einstein-Gauss-Bonnet field
equations with a cosmological term and a different than b. We then examine
whether this solution for the trace does solve the remaining field equations.
We find that it does not in general, unless the Gauss-Bonnet coupling is such
that the field equations have a unique maximally symmetric solution.Comment: 10 pages, no figures, references added. Last version for CQ
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