José Natário

Asymptotic quasinormal frequencies for black holes in nonasymptotically flat space¿times

The exact computation of asymptotic quasinormal frequencies is a technical problem which involves the analytic continuation of a Schrodinger-type equation to the complex plane and then performing a method of monodromy matching at several poles in the plane. While this method was successfully used in asymptotically flat space–time, as applied to both the Schwarzschild and Reissner–Nordstro/m solutions, its extension to nonasymptotically flat space–times has not been achieved yet. In this work it is shown how to extend the method to this case, with the explicit analysis of Schwarzschild–de Sitter and large Schwarzschild–anti–de Sitter black holes, both in four dimensions. We obtain, for the first time, analytic expressions for the asymptotic quasinormal frequencies of these black hole space–times, and our results match previous numerical calculations with great accuracy. We also list some results concerning the general classification of asymptotic quasinormal frequencies in d-dimensional space–times.

Mathisson's helical motions for a spinning particle: Are they unphysical?

It has been asserted in the literature that Mathissons helical motions are unphysical, with the argument that their radius can be arbitrarily large. We revisit Mathissons helical motions of a free spinning particle, and observe that such statement is unfounded. Their radius is finite and confined to the disk of centroids. We argue that the helical motions are perfectly valid and physically equivalent descriptions of the motion of a spinning body, the difference between them being the choice of the representative point of the particle, thus a gauge choice. We discuss the kinematical explanation of these motions, and we dynamically interpret them through the concept of hidden momentum. We also show that, contrary to previous claims, the frequency of the helical motions coincides, even in the relativistic limit, with the zitterbewegung frequency of the Dirac equation for the electron.

Warp drive with zero expansion

It is commonly believed that Alcubierres warp drive works by contracting space in front of the warp bubble and expanding the space behind it. We show that this contraction/expansion is but a marginal consequence of the choice made by Alcubierre and explicitly construct a similar spacetime where no contraction/expansion occurs. Global and optical properties of warp-drive spacetimes are also discussed.

Linking, Legendrian Linking and Causality

The set N of all null geodesics of a globally hyperbolic

On the Global Uniqueness for the Einstein–Maxwell-Scalar Field System with a Cosmological Constant: Part 3. Mass Inflation and Extendibility of the Solutions

(d + 1)

Painlevé–Gullstrand coordinates for the Kerr solution

-dimensional spacetime

Test fields cannot destroy extremal black holes

(M, g)

Gravito-electromagnetic analogies

is naturally a smooth

Spherical linear waves in de Sitter spacetime

(2d - 1)

Center of Mass, Spin Supplementary Conditions, and the Momentum of Spinning Particles

-dimensional contact manifold. The sky of an event x in M is the subset X of N consisting of all null geodesics through x, and is an embedded Legendrian submanifold of N diffeomorphic to