76 research outputs found
Anisotropic scale invariant spacetimes and black holes in Zwei-Dreibein Gravity
We show that Zwei-Dreibein Gravity (ZDG), a bigravity theory recently proposed by Bergshoeff, de Haan, Hohm, Merbis, and Townsend in ref. [1], admits exact solutions with anisotropic scale invariance. These type of geometries are the three-dimensional analogues of the spacetimes which were proposed as gravity duals for condensed matter systems. In particular, we find Schrödinger invariant spaces as well as Lifshitz spaces with arbitrary dynamical exponent z. We also find black holes that are asymptotically Lifshitz with z = 3, showing that these (non-constant curvature) solutions of New Massive Gravity (NMG) are persistent after the introduction of the infinite tower of higher-curvature terms of ZDG, provided a renormalization of the parameters. Black holes in asymptotically warped Anti-de Sitter spaces are also found. Interestingly, in almost all the geometries studied in this work, the metric associated with the second dreibein turns out to be equivalent, up to a constant global factor, to the first one. This phenomenon has been previously observed in other bigravity theories in asymptotically flat and asymptotically Anti-de Sitter backgrounds. However, for the particular case of the z = 3 Lifshitz black hole, here we found that the second metric corresponds to a different black hole that coincides with the former only in the asymptotic region. In fact, we find a new family of z = 3 black holes that corresponds to a one-parameter deformation of the NMG solution.Fil: Goya, Andrés Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin
The Brown-York mass of black holes in Warped Anti-de Sitter space
We give a direct computation of the mass of black holes in Warped Anti-de
Sitter space (WAdS) in terms of the Brown-York stress-tensor at the boundary.
This permits to explore to what extent the holographic renormalization
techniques can be applied to such type of deformation of AdS. We show that,
despite some components of the boundary stress-tensor diverge and resist to be
regularized by the introduction of local counterterms, the precise combination
that gives the quasilocal energy density yields a finite integral. The result
turns out to be in agreement with previous computations of the black hole mass
obtained with different approaches. This is seen to happen both in the case of
Topologically Massive Gravity and of the so-called New Massive Gravity. Here,
we focus our attention on the latter. We observe that, despite other conserved
charges diverge in the near boundary limit, the finite part in the large radius
expansion captures the physically relevant contribution. We compute the black
hole angular momentum in this way and we obtain a result that is in perfect
agreement with previous calculations.Comment: 8 pages. v2 discussion and appendix added, references added. To
appear in JHE
Quasilocal energy for three-dimensional massive gravity solutions with chiral deformations of AdS boundary conditions
We consider critical gravity in three dimensions; that is, the New Massive
Gravity theory formulated about Anti-de Sitter (AdS) space with the specific
value of the graviton mass for which it results dual to a two-dimensional
conformal field theory with vanishing central charge. As it happens with Kerr
black holes in four-dimensional critical gravity, in three-dimensional critical
gravity the Banados-Teitelboim-Zanelli black holes have vanishing mass and
vanishing angular momentum. However, provided suitable asymptotic conditions
are chosen, the theory may also admit solutions carrying non-vanishing charges.
Here, we give simple examples of exact solutions that exhibit falling-off
conditions that are even weaker than those of the so-called Log-gravity. For
such solutions, we define the quasilocal stress-tensor and use it to compute
conserved charges. Despite the drastic deformation of AdS3 asymptotic, these
solutions have finite mass and angular momentum.Comment: 7 pages. v3: Typos corrected. Version accepted for publicatio
Boundary stress tensor and asymptotically AdS3 non-Einstein spaces at the chiral point
Chiral gravity admits asymptotically AdS3 solutions that are not locally
equivalent to AdS3; meaning that solutions do exist which, while obeying the
strong boundary conditions usually imposed in General Relativity, happen not to
be Einstein spaces. In Topologically Massive Gravity (TMG), the existence of
non-Einstein solutions is particularly connected to the question about the role
played by complex saddle points in the Euclidean path integral. Consequently,
studying (the existence of) non-locally AdS3 solutions to chiral gravity is
relevant to understand the quantum theory. Here, we discuss a special family of
non-locally AdS3 solutions to chiral gravity. In particular, we show that such
solutions persist when one deforms the theory by adding the higher-curvature
terms of the so-called New Massive Gravity (NMG). Moreover, the addition of
higher-curvature terms to the gravity action introduces new non-locally AdS3
solutions that have no analogues in TMG. Both stationary and time-dependent,
axially symmetric solutions that asymptote AdS3 space without being locally
equivalent to it appear. Defining the boundary stress-tensor for the full
theory, we show that these non-Einstein geometries have associated vanishing
conserved charges.Comment: 8 pages. v2 minor typos correcte
Logarithmic AdS Waves and Zwei-Dreibein Gravity
We show that the parameter space of Zwei-Dreibein Gravity (ZDG) in AdS3
exhibits critical points, where massive graviton modes coincide with pure gauge
modes and new `logarithmic' modes appear, similar to what happens in New
Massive Gravity. The existence of critical points is shown both at the
linearized level, as well as by finding AdS wave solutions of the full
non-linear theory, that behave as logarithmic modes towards the AdS boundary.
In order to find these solutions explicitly, we give a reformulation of ZDG in
terms of a single Dreibein, that involves an infinite number of derivatives. At
the critical points, ZDG can be conjectured to be dual to a logarithmic
conformal field theory with zero central charges, characterized by new
anomalies whose conjectured values are calculated.Comment: 20 page
Clasificadora de patata de frecuencia natural
En este trabajo se desarrollara una criba de frecuencia natural para el calibrado de
patatas en diferentes tamaños.
La motivación para realizar trabajo surge de la idea de mejorar los sistemas de
clasificado de hortalizas de hoy en día, concretamente el de patatas.
El consumo de patatas en la actualidad es muy elevado, ya que se considera un
alimento básico en nuestras vidas, por tanto su comercialización está asegurada. En la
comercialización, la patata, debe cumplir unos requisitos obligatorios establecidos por
la ley.
El presente proyecto trata del diseño, para su posterior fabricación, de una criba para
la clasificación de patata en fresco en siete tamaños diferentes aplicando la tecnología
de vibración basada en la frecuencia natural de los materiales. Para ello una vez
determinadas las luces y superficies de malla idóneas para cada tamaño a clasificar,
elegiremos el soporte físico que las va a soportar.
Este modo de clasificar las patatas es un sistema novedoso, ya que consigue un
importante ahorro de energíaGraduado o Graduada en Ingeniería en Diseño Mecánico por la Universidad Pública de NavarraDiseinu Mekanikoko Ingeniaritzan Graduatua Nafarroako Unibertsitate Publikoa
Chemical potential driven phase transition of black holes in anti-de Sitter space
Einstein-Maxwell theory conformally coupled to a scalar field in D dimensions may exhibit a phase transition at low temperature whose end point is an asymptotically anti-de Sitter black hole with a scalar field profile that is regular everywhere outside and on the horizon. This provides a tractable model to study the phase transition of hairy black holes in anti-de Sitter space in which the backreaction on the geometry can be solved analytically.Fil: Galante, Mariano. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Giribet, Gaston Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina. Université Libre de Bruxelles; Bélgica. Pontificia Universidad Católica de Valparaíso; ChileFil: Goya, Andrés Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; ArgentinaFil: Oliva, Julio. Universidad de Concepción; Chil
Critical points of the exotic massive 3D gravity
Exotic Massive 3D Gravity (EMG) is a higher order generalization of Topologically Massive Gravity. As in other theories of this sort, the conserved charges associated to the asymptotic diffeomorphisms that preserve the boundary conditions in AdS3 spacetime span two copies of the Virasoro algebra with non-vanishing central charges. Here, we discuss the values of these central charges and the corresponding conformal anomaly in relation to the phase space of the theory.Fil: Giribet, Gaston Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Goya, Andrés Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Lavia, Edmundo. Consejo Nacional de Investigaciones Científicas y Técnicas. Unidad de Investigación y Desarrollo Estratégico para la Defensa. Ministerio de Defensa. Unidad de Investigación y Desarrollo Estratégico para la Defensa; Argentina. Ministerio de Defensa. Armada Argentina. Dirección Gral. de Investigación y Desarrollo de la Ara. Dirección de Investigación de la Armada; ArgentinaFil: Oliva, Julio. Universidad de Concepción; Chil
Magnetic Nanoparticles for Power Absorption: optimizing size, shape and magnetic properties
We present a study on the magnetic properties of naked and silica-coated
Fe3O4 nanoparticles with sizes between 5 and 110 nm. Their efficiency as
heating agents was assessed through specific power absorption (SPA)
measurements as a function of particle size and shape. The results show a
strong dependence of the SPA with the particle size, with a maximum around 30
nm, as expected for a Neel relaxation mechanism in single-domain particles. The
SiO2 shell thickness was found to play an important role in the SPA mechanism
by hindering the heat outflow, thus decreasing the heating efficiency. It is
concluded that a compromise between good heating efficiency and surface
functionality for biomedical purposes can be attained by making the SiO2
functional coating as thin as possible.Comment: 15 pages, 7 figures, 2 table
3d Quantum Gravity Partition Function at 3 Loops: a brute force computation
The partition function of 3-dimensional quantum gravity has been argued to be
1-loop exact. Here, we verify the vanishing of higher-orders in perturbation
theory by explicit computation in the second-order, metric formulation at
3-loops. The number of 1-particle irreducible Feynman diagrams involving both
gravitons and ghosts turns out to be 17. Using dimensional regularization, we
solve all the diagrams. At 2-loops, we find that all such diagrams vanish
separately after regularization. At 3-loops, in contrast, a series of
remarkable cancellations between different diagrams takes place, with 9
diagrams beautifully conspiring to yield a vanishing result. Our techniques are
suitable to be applied to higher loops as well as to similar computations in
higher dimensions.Comment: 6 pages, 8 figure
- …