350 research outputs found
Vacuum thin shell solutions in five-dimensional Lovelock gravity
Junction conditions for vacuum solutions in five-dimensional
Einstein-Gauss-Bonnet gravity are studied. We focus on those cases where two
spherically symmetric regions of space-time are joined in such a way that the
induced stress tensor on the junction surface vanishes. So a spherical vacuum
shell, containing no matter, arises as a boundary between two regions of the
space-time. Such solutions are a generalized kind of spherically symmetric
empty space solutions, described by metric functions of the class . New
global structures arise with surprising features. In particular, we show that
vacuum spherically symmetric wormholes do exist in this theory. These can be
regarded as gravitational solitons, which connect two asymptotically (Anti)
de-Sitter spaces with different masses and/or different effective cosmological
constants. We prove the existence of both static and dynamical solutions and
discuss their (in)stability under perturbations that preserve the symmetry.
This leads us to discuss a new type of instability that arises in
five-dimensional Lovelock theory of gravity for certain values of the coupling
of the Gauss-Bonnet term.Comment: 9 pages. This is an extended version of the authors' contribution to
the Proceedings of the Marcel Grossmann Meeting, held in Paris, 12-18 July
200
Superstrings on AdS3 at k=1
We study superstring theory in three dimensional Anti-de Sitter spacetime
with NS-NS flux, focusing on the case where the radius of curvature is equal to
the string length. This corresponds to the critical level k=1 in the
Wess-Zumino-Witten description. Previously, it was argued that a transition
takes place at this special radius, from a phase dominated by black holes at
larger radius to one dominated by long strings at smaller radius. We argue that
the infinite tower of modes that become massless at k=1 is a signal of this
transition. We propose a simple two-dimensional conformal field theory as the
holographic dual to superstring theory at k=1. As evidence for our conjecture,
we demonstrate that at large N our putative dual exactly reproduces the full
spectrum of the long strings of the weakly coupled string theory, including
states unprotected by supersymmetry.Comment: 29 pages, one figure. An equivalent construction of the dual orbifold
CFT has been added, together with a discussion of the short string spectrum
and additional observations on interaction
Komar Integrals in Higher (and Lower) Derivative Gravity
The Komar integral relation of Einstein gravity is generalized to Lovelock
theories of gravity. This includes, in particular, a new boundary integral for
the Komar mass in Einstein gravity with a nonzero cosmological constant, which
has a finite result for asymptotically AdS black holes, without the need for an
infinite background subtraction. Explicit computations of the Komar mass are
given for black holes in pure Lovelock gravities of all orders and in general
Gauss-Bonnet theories.Comment: 16 pages; v2 - references and comment on relation to Noether charge
method adde
On Black Hole Stability in Critical Gravities
We consider extended cosmological gravities with Ricci tensor and scalar
squared terms in diverse dimensions. These theories admit solutions of Einstein
metrics, including the Schwarzschild-Tangherlini AdS black holes, whose mass
and entropy vanish at the critical point. We perform linearized analysis around
the black holes and show that in general the spectrum consists of the usual
spin-2 massless and ghost massive modes. We demonstrate that there is no
exponentially-growing tachyon mode in the black holes. At the critical point,
the massless spin-2 modes have zero energy whilst the massive spin-2 modes are
replaced by the log modes. There always exist certain linear combination of
massless and log modes that has negative energy. Thus the stability of the
black holes requires that the log modes to be truncated out by the boundary
condition.Comment: 16 pages, minor corrections, further comments and references adde
Global phase time and path integral for string cosmological models
A global phase time is identified for homogeneous and isotropic cosmological
models yielding from the low energy effective action of closed bosonic string
theory. When the Hamiltonian constraint allows for the existence of an
intrinsic time, the quantum transition amplitude is obtained by means of the
usual path integral procedure for gauge systems.Comment: 12 pages, added reference
Relativistic effects on the nuclear magnetic shielding tensor
A new approach for calculating relativistic corrections to the nuclear magnetic shieldings is presented. Starting from a full relativistic second order perturbation theory expression a two-component formalism is constructed by transforming matrix elements using the elimination of small component scheme and separating out the contributions from the no-virtual pair and the virtual pair part of the second order corrections to the energy. In this way we avoid a strong simplification used previously in the literature. We arrive at final expressions for the relativistic corrections which are equivalent to those of Fukui et al. J. Chem Phys. 105, 3175 (1996) and at some other additional terms correcting both the paramagnetic and the diamagnetic part of the nuclear magnetic shielding. Results for some relativistic corrections to the shieldings of the heavy and light nuclei in HX and CHÈX (X=Br,I) at both random phase and second order polarization propagator approach levels are given.Fil: Melo, Juan Ignacio. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de FĂsica de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de FĂsica de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de FĂsica; ArgentinaFil: Ruiz de Azua, MartĂn CĂ©sar. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de FĂsica; ArgentinaFil: Giribet, Claudia Gloria. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de FĂsica; ArgentinaFil: Aucar, Gustavo Adolfo. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura. Departamento de FĂsica; ArgentinaFil: Romero, Rodolfo Horacio. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura. Departamento de FĂsica; Argentin
Simple compactifications and Black p-branes in Gauss-Bonnet and Lovelock Theories
We look for the existence of asymptotically flat simple compactifications of
the form in -dimensional gravity theories with higher
powers of the curvature. Assuming the manifold to be spherically
symmetric, it is shown that the Einstein-Gauss-Bonnet theory admits this class
of solutions only for the pure Einstein-Hilbert or Gauss-Bonnet Lagrangians,
but not for an arbitrary linear combination of them. Once these special cases
have been selected, the requirement of spherical symmetry is no longer relevant
since actually any solution of the pure Einstein or pure Gauss-Bonnet theories
can then be toroidally extended to higher dimensions. Depending on and the
spacetime dimension, the metric on may describe a black hole or a
spacetime with a conical singularity, so that the whole spacetime describes a
black or a cosmic -brane, respectively. For the purely Gauss-Bonnet theory
it is shown that, if is four-dimensional, a new exotic class of black
hole solutions exists, for which spherical symmetry can be relaxed.
Under the same assumptions, it is also shown that simple compactifications
acquire a similar structure for a wide class of theories among the Lovelock
family which accepts this toroidal extension.
The thermodynamics of black -branes is also discussed, and it is shown
that a thermodynamical analogue of the Gregory-Laflamme transition always
occurs regardless the spacetime dimension or the theory considered, hence not
only for General Relativity.
Relaxing the asymptotically flat behavior, it is also shown that exact black
brane solutions exist within a very special class of Lovelock theories.Comment: 30 pages, no figures, few typos fixed, references added, final
version for JHE
High Conservatism in the Composition of Scent Gland Secretions in Cyphophthalmid Harvestmen: Evidence from Pettalidae
The scent gland secretion of Austropurcellia forsteri was analyzed by gas chromatographyâmass spectrometry, providing the first description of the secretion chemistry in the cyphophthalmid family Pettalidae. The secretion contained a total of 21 compounds: About 60% of the whole secretion consisted of a series of saturated, mono-unsaturated and doubly unsaturated methylketones, from C11 to C15, with a cluster of saturated and mono-unsaturated C13-methylketones dominating. A second fraction included several naphthoquinones such as 1,4-naphthoquinone (ca. 20% of secretion), 6-methyl-1,4-naphthoquinone (ca. 17%), and minor amounts of chloronaphthoquinones (ca. 2%). When compared with scent gland compositions of other representatives of cyphophthalmids (e.g. from families Sironidae and Stylocellidae), a highly conservative chemistry of cyphophthalmid secretions is apparent, based on a restricted number of methylketones and naphthoquinones
Breit interaction effects in relativistic theory of the nuclear spin-rotation tensor
In this work, relativistic effects on the nuclear spin-rotation (SR) tensor originated in the electronnucleus and electron-electron Breit interactions are analysed. To this end, four-component numerical calculations were carried out in model systems HX (X=H,F,Cl,Br,I). The electron-nucleus Breit interaction couples the electrons and nuclei dynamics giving rise to a purely relativistic contribution to the SR tensor. Its leading order in 1/c is of the same value as that of relativistic corrections on the usual second order expression of the SR tensor considered in previous work [I. A. Aucar, S. S. GĂłmez, J. I. Melo, C. G. Giribet, and M. C. Ruiz de AzĂșa, J. Chem. Phys. 138, 134107 (2013)], and therefore it is absolutely necessary to establish its relative importance. For the sake of completeness, the corresponding effect originating in the electron-electron Breit interaction is also considered. It is verified that in all cases these Breit interactions yield only very small corrections to the SR tensors of both the X and H nuclei in the present series of compounds. Results of the present work strongly suggest that in order to achieve experimental accuracy in the theoretical study of the SR tensor both electron-nucleus and electron-electron Breit effects can be safely neglected.Fil: Aucar, Ignacio AgustĂn. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Nordeste. Instituto de Modelado e InnovaciĂłn TecnolĂłgica; ArgentinaFil: Gomez, Sergio Santiago. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Nordeste. Instituto de Modelado e InnovaciĂłn TecnolĂłgica; ArgentinaFil: Giribet, Claudia Gloria. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de FĂsica de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de FĂsica; ArgentinaFil: Ruiz de Azua, Martin Cesar. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de FĂsica de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de FĂsica; Argentin
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