arXiv subjects

Nelson Zamorano

Publications and source records attributed to Nelson Zamorano.

7 recordsLinked to original sources

arXiv2013

de Sitter Entropy from a lower dimensional black hole

An alternative method to compute the entropy of de Sitter spacetime for dimensions higher than or equal to five is presented. It is shown that de Sitter entropy may be obtained from the Bekenstein-Hawking entropy of a lower-dimensional black hole. This result follows from the existence of a one-to-one correspondence between de Sitter and a spacetime containing a black hole localized on a p-brane. Under this correspondence and due to the holographic principle, the entropy of a five-dimensional de Sitter space may be obtained from that of a BTZ black hole localized on a 2-brane. For dimensions higher than five, de Sitter entropy is identified with the entropy of a Schwarzschild-de Sitter black hole localized on a (d-3)-brane.

gr-qc↗

arXiv2011

Analogue black hole in magnetohydrodynamics

We consider an irrotational plasma fluid evolving under the effect of a background magnetic field. The magnetohydrodynamic formalism is used to describe the electromagnetic waves and the dynamics is described by a scalar field that follows a second order differential equation. This equation can also be recovered as the wave equation associated to a field in a curved space-time. Through this analogy we recreate a sonic horizon, equivalent to those found in perfect fluid theories. However, in this case, the magnetic field creates a pressure in the plasma which contributes to the magnetoacoustic speed that builds the horizon. This effect enhances the temperature produced by the Hawking radiation expected from this analogue black hole, and eventually, making its experimental detection worth to consider.

gr-qc↗

arXiv2010

Kerr-Schild Method and Geodesic Structure in Codimension-2 Brane Black Holes

We consider the black hole solutions of five-dimensional gravity with a Gauss-Bonnet term in the bulk and an induced gravity term on a 2-brane of codimension-2. Applying the Kerr-Schild method we derive additional solutions which include charge and angular momentum. To improve our understanding of this geometry we study the geodesic structure of such spacetimes.

gr-qc↗

arXiv2007

Compactification in first order gravity

The Kaluza-Klein compactification process is applied in five dimensions to CS gravity, for the anti-de Sitter and Poincaré groups, using the first order formalism. In this context some solutions are found and analyzed. Also, the conserved charges associated to the solutions are computed.

hep-th↗

arXiv2007

Conformal Gravity from AdS/CFT mechanism

We explicitly calculate the induced gravity theory at the boundary of an asymptotically Anti-de Sitter five dimensional Einstein gravity. We also display the action that encodes the dynamics of radial diffeomorphisms. It is found that the induced theory is a four dimensional conformal gravity plus a scalar field. This calculation confirms some previous results found by a different approach.

hep-th↗

arXiv1997

A Wormhole at the core of an infinite cosmic string

We study a solution of Einstein's equations that describes a straight cosmic string with a variable angular deficit, starting with a $2 π$ deficit at the core. We show that the coordinate singularity associated to this defect can be interpreted as a traversible wormhole lodging at the the core of the string. A negative energy density gradually decreases the angular deficit as the distance from the core increases, ending, at radial infinity, in a Minkowski spacetime. The negative energy density can be confined to a small transversal section of the string by gluing to it an exterior Gott's like solution, that freezes the angular deficit existing at the matching border. The equation of state of the string is such that any massive particle may stay at rest anywhere in this spacetime. In this sense this is 2+1 spacetime solution.

gr-qc↗

arXiv1997

Numerical stability of a family of Osipkov-Merrit models

We have investigated the stability of a set of non-rotating anisotropic spherical models with a phase-space distribution function of the Osipkov-Merritt type. The velocity distribution in these models is isotropic near the center and becomes radially anisotropic at large radii. They are special members of the family studied by Dehnen and Tremaine et al. where the mass density has a power-law cusp $ρ\propto r^{-γ}$ at small radii and decays as $ρ\propto r^{-4}$ at large radii. The radial-orbit instability of models with $γ$ = 0, 1/2, 1, 3/2, and 2, was studied using an N-body code written by one of us and based on the `self-consistent field' method developed by Hernquist and Ostriker. These simulations have allowed us to delineate a boundary in the $(γ,r_{a})$-plane that separates the stable from the unstable models. This boundary is given by $2T_{r}/T_{t} = 2.31 \pm 0.27$, for the ratio of the total radial to tangential kinetic energy. We also found that the stability criterion $df/dQ\le 0$, recently raised by Hjorth, gives lower values compared with our numerical results.

astro-ph↗