1,199 research outputs found
Non-Gravitating Scalar Field in the FRW Background
We study interacting scalar field theory non-minimally coupled to gravity in
the FRW background. We show that for a specific choice of interaction terms,
the energy-momentum tensor of the scalar field vanishes, and as a result the
scalar field does not gravitate. The naive space dependent solution to
equations of motion gives rise to singular field profile. We carefully analyze
the energy-momentum tensor for such a solution and show that the singularity of
the solution gives a subtle contribution to the energy-momentum tensor. The
space dependent solution therefore is not non-gravitating. Our conclusion is
applicable to other space-time dependent non-gravitating solutions as well. We
study hybrid inflation scenario in this model when purely time dependent
non-gravitating field is coupled to another scalar field.Comment: 7 Pages, 2 figures, RevTeX4, v2:added a section on regularized
energy-momentum tensor, references and conclusions modifie
Stability properties of black holes in self-gravitating nonlinear electrodynamics
We analyze the dynamical stability of black hole solutions in
self-gravitating nonlinear electrodynamics with respect to arbitrary linear
fluctuations of the metric and the electromagnetic field. In particular, we
derive simple conditions on the electromagnetic Lagrangian which imply linear
stability in the domain of outer communication. We show that these conditions
hold for several of the regular black hole solutions found by Ayon-Beato and
Garcia.Comment: 15 pages, no figure
Generalized Convexity in Multiobjective Programming
AbstractFor the scalar programming problem, some characterizations for optimal solutions are known. In these characterizations convexity properties play a very important role. In this work, we study characterizations for multiobjective programming problem solutions when functions belonging to the problem are differentiable. These characterizations need some conditions of convexity. In differentiable scalar programming problems the concept of invexity is very important. We prove that it is also necessary for the multiobjective programming problem and give some characterizations of multiobjective programming problem solutions under weaker conditions. We define analogous concepts to those of stationary points and to the conditions of Kuhn–Tucker and Fritz–John for the multiobjective programming problem
Proximal and distal spinal neurons innervating multiple synergist and antagonist motor pools
Motoneurons control muscle contractions, and their recruitment by premotor circuits is tuned to produce accurate motor behaviours. To understand how these circuits coordinate movement across and between joints, it is necessary to understand whether spinal neurons pre-synaptic to motor pools have divergent projections to more than one motoneuron population. Here, we used modified rabies virus tracing in mice to investigate premotor INs projecting to synergist flexor or extensor motoneurons, as well as those projecting to antagonist pairs of muscles controlling the ankle joint. We show that similar proportions of premotor neurons diverge to synergist and antagonist motor pools. Divergent premotor neurons were seen throughout the spinal cord, with decreasing numbers but increasing proportion with distance from the hindlimb enlargement. In the cervical cord, divergent long descending propriospinal neurons were found in contralateral lamina VIII, had large somata, were neither glycinergic, nor cholinergic, and projected to both lumbar and cervical motoneurons. We conclude that distributed spinal premotor neurons coordinate activity across multiple motor pools and that there are spinal neurons mediating co-contraction of antagonist muscles
Apparent dominance of the G1-G3 genetic cluster of echinococcus granulosus strains in the central inland region of Portugal
Infection by the larval stage of the cestode Echinococcus granulosus causes a disease
known as cystic echinococcosis or hydatidosis, which is one of the most widespread
zoonotic infections of veterinary and medical importance. Numerous studies have
shown that E. granulosus exists as a complex of strains differing in a wide variety of
criteria. Ten distinct genotypes (G1-G10) have been identified with potential impact on
the pathology, epidemiology and the effect of the measures implemented for the control
of hydatidosis. Our main objective was to carry out a preliminary analysis of the
genotypes of E. granulosus circulating in the central inland region of Portugal.
Parasite samples (hydatid cysts, n=27) were isolated from the liver and lung of sheep
and cattle. The DNA extracted from protoscoleces isolated from the fertile cysts served
a template for the PCR amplification of part of the mitochondrial cytochrome c oxidase
subunit 1 (cox1), ATP synthase F0 subunit 6 (atp6) as well as the large (rrnL/16S) and
small (rrnS/12S) ribosomal RNA genes. Similarity searches with homologous
sequences in the databanks indicated very high similarity with references assigned to the
G1, G3 and/or G1-G3 complex of Echinococcus strains. Phylogenetic analysis
(Bayesian approach) supported these observations, and confirmed the assignment of all
the analyzed sequences to the G1-G3 genetic cluster
On the new massive gravity and AdS/CFT
Demanding the existence of a simple holographic -theorem, it is shown that
a general (parity preserving) theory of gravity in 2+1 dimensions involving
upto four derivative curvature invariants reduces to the new massive gravity
theory. We consider extending the theory including upto six derivative
curvature invariants. Black hole solutions are presented and consistency with
1+1 CFTs is checked. We present evidence that bulk unitarity is still in
conflict with a positive CFT central charge for generic choice of parameters.
However, for a special choice of parameters appearing in the four and six
derivative terms reduces the linearized equations to be two derivative, thereby
ameliorating the unitarity problem.Comment: 16 pages, 2 figures. v4: typo correcte
Black hole solutions in Euler-Heisenberg theory
We construct static and spherically symmetric black hole solutions in the
Einstein-Euler-Heisenberg (EEH) system which is considered as an effective
action of a superstring theory. We considered electrically charged,
magnetically charged and dyon solutions. We can solve analytically for the
magnetically charged case. We find that they have some remarkable properties
about causality and black hole thermodynamics depending on the coupling
constant of the EH theory and , though they have central singularity as
in the Schwarzschild black hole.Comment: 8 pages, 13 figures, figures corrected and some comments adde
Analytic Lifshitz black holes in higher dimensions
We generalize the four-dimensional R^2-corrected z=3/2 Lifshitz black hole to
a two-parameter family of black hole solutions for any dynamical exponent z and
for any dimension D. For a particular relation between the parameters, we find
the first example of an extremal Lifshitz black hole. An asymptotically
Lifshitz black hole with a logarithmic decay is also exhibited for a specific
critical exponent depending on the dimension. We extend this analysis to the
more general quadratic curvature corrections for which we present three new
families of higher-dimensional D>=5 analytic Lifshitz black holes for generic
z. One of these higher-dimensional families contains as critical limits the z=3
three-dimensional Lifshitz black hole and a new z=6 four-dimensional black
hole. The variety of analytic solutions presented here encourages to explore
these gravity models within the context of non-relativistic holographic
correspondence.Comment: 14 page
Tricritical gravity waves in the four-dimensional generalized massive gravity
We construct a generalized massive gravity by combining quadratic curvature
gravity with the Chern-Simons term in four dimensions. This may be a candidate
for the parity-odd tricritical gravity theory. Considering the AdS vacuum
solution, we derive the linearized Einstein equation, which is not similar to
that of the three dimensional (3D) generalized massive gravity. When a
perturbed metric tensor is chosen to be the Kerr-Schild form, the linearized
equation reduces to a single massive scalar equation. At the tricritical points
where two masses are equal to -1 and 2, we obtain a log-square wave solution to
the massive scalar equation. This is compared to the 3D tricritical generalized
massive gravity whose dual is a rank-3 logarithmic conformal field theory.Comment: 17 pages, 1 figure, version to appear in EPJ
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