1,869 research outputs found
Exact quasinormal modes for a special class of black holes
Analytic exact expressions for the quasinormal modes of scalar and
electromagnetic perturbations around a special class of black holes are found
in d\ge3 dimensions. It is shown that, the size of the black hole provides a
bound for the angular momentum of the perturbation. Quasinormal modes appear
when this bound is fulfilled, otherwise the excitations become purely damped.Comment: 8 pages, no figures. Slightly updated version of the plenary talk
given at the General Relativity Conference: "50 Years of FaMAF and Workshop
on Global Problems in Relativity", hosted during November 2006 at FaMAF,
Universidad Nacional de Cordoba, Cordoba, Argentina
Many-body theory of spin-current driven instabilities in magnetic insulators
We consider a magnetic insulator in contact with a normal metal. We derive a
self-consistent Keldysh effective action for the magnon gas that contains the
effects of magnon-magnon interactions and contact with the metal to lowest
order. Self-consistent expressions for the dispersion relation, temperature and
chemical potential for magnons are derived. Based on this effective action, we
study instabilities of the magnon gas that arise due to spin-current flowing
across the interface between the normal metal and the magnetic insulator. We
find that the stability phase diagram is modified by an interference between
magnon-magnon interactions and interfacial magnon-electron coupling. These
effects persist at low temperatures and for thin magnetic insulators.Comment: 10 pages and 5 figure
A new species of Liolaemus related to L. nigroviridis from the Andean highlands of Central Chile (Iguania, Liolaemidae)
Indexación: Web of Science; Scopus.The Liolaemus nigroviridis group is a clade of highland lizards endemic to Chile. These species are distributed from northern to central Chile, and currently there are no cases of sympatric distribution. This study describes a new species, Liolaemus uniformis sp. n., from this group, and provides a detailed morphological characterization and mitochondrial phylogeny using cytochrome-b. Liolaemus uniformis was found in sympatry with L. nigroviridis but noticeably differed in size, scalation, and markedly in the color pattern, without sexual dichromatism. This new species has probably been confused with L. monticola and L. bellii, both of which do not belong to the nigroviridis group. The taxonomic issues of this group that remain uncertain are also discussed.https://zookeys.pensoft.net/articles.php?id=601
Revisiting the asymptotic dynamics of General Relativity on AdS
The dual dynamics of Einstein gravity on AdS supplemented with boundary
conditions of KdV-type is identified. It corresponds to a two-dimensional field
theory at the boundary, described by a novel action principle whose field
equations are given by two copies of the "potential modified KdV equation". The
asymptotic symmetries then transmute into the global Noether symmetries of the
dual action, giving rise to an infinite set of commuting conserved charges,
implying the integrability of the system. Noteworthy, the theory at the
boundary is non-relativistic and possesses anisotropic scaling of Lifshitz
type.Comment: 18 page
Black holes, parallelizable horizons and half-BPS states for the Einstein-Gauss-Bonnet theory in five dimensions
Exact vacuum solutions with a nontrivial torsion for the
Einstein-Gauss-Bonnet theory in five dimensions are constructed. We consider a
class of static metrics whose spacelike section is a warped product of the real
line with a nontrivial base manifold endowed with a fully antisymmetric
torsion. It is shown requiring solutions of this sort to exist, fixes the
Gauss-Bonnet coupling such that the Lagrangian can be written as a Chern-Simons
form. The metric describes black holes with an arbitrary, but fixed, base
manifold. It is shown that requiring its ground state to possess unbroken
supersymmetries, fixes the base manifold to be locally a parallelized
three-sphere. The ground state turns out to be half-BPS, which could not be
achieved in the absence of torsion in vacuum. The Killing spinors are
explicitly found.Comment: 11 pages, no figures, notation clarified; version accepted for
publication in Physical Review
Thermodynamics from a scaling Hamiltonian
There are problems with defining the thermodynamic limit of systems with
long-range interactions; as a result, the thermodynamic behavior of these types
of systems is anomalous. In the present work, we review some concepts from both
extensive and nonextensive thermodynamic perspectives. We use a model, whose
Hamiltonian takes into account spins ferromagnetically coupled in a chain via a
power law that decays at large interparticle distance as for
. Here, we review old nonextensive scaling. In addition, we
propose a new Hamiltonian scaled by that
explicitly includes symmetry of the lattice and dependence on the size, , of
the system. The new approach enabled us to improve upon previous results. A
numerical test is conducted through Monte Carlo simulations. In the model,
periodic boundary conditions are adopted to eliminate surface effects.Comment: 12 pages, 2 figures, submitted for publication to Phys. Rev.
Standard General Relativity from Chern-Simons Gravity
Chern-Simons models for gravity are interesting because they provide with a
truly gauge-invariant action principle in the fiber-bundle sense. So far, their
main drawback has largely been the perceived remoteness from standard General
Relativity, based on the presence of higher powers of the curvature in the
Lagrangian (except, remarkably, for three-dimensional spacetime). Here we
report on a simple model that suggests a mechanism by which standard General
Relativity in five-dimensional spacetime may indeed emerge at a special
critical point in the space of couplings, where additional degrees of freedom
and corresponding "anomalous" Gauss-Bonnet constraints drop out from the
Chern-Simons action. To achieve this result, both the Lie algebra g and the
symmetric g-invariant tensor that define the Chern-Simons Lagrangian are
constructed by means of the Lie algebra S-expansion method with a suitable
finite abelian semigroup S. The results are generalized to arbitrary odd
dimensions, and the possible extension to the case of eleven-dimensional
supergravity is briefly discussed.Comment: 6 pages, no figures; v2: published versio
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