Delliou, Morgan Le, Mena, Filipe C., Mimoso, José Pedro
We discuss the existence of a dividing shell separating expanding and collapsing regions in spherically symmetric solutions with pressure. We obtain gauge invariant conditions relating not only the...
Mimoso, José Pedro, Delliou, Morgan Le, Mena, Filipe C.
We investigate spherically symmetric perfect fluid spacetimes and discuss the existence and stability of a dividing shell separating expanding and collapsing regions. We perform a 3+1 splitting and...
Formation of Higher-dimensional Topological Black Holes (2009)
Mena, Filipe C., Natario, Jose, Tod, Paul
We study higher dimensional gravitational collapse to topological black holes in two steps. Firstly, we construct some (n+2)-dimensional collapsing space-times, which include generalised...
First order perturbations of the Einstein-Straus and Oppenheimer-Snyder models (2008)
Mars, Marc, Mena, Filipe C., Vera, Raül
We derive the linearly perturbed matching conditions between a Schwarzschild spacetime region with stationary and axially symmetric perturbations and a FLRW spacetime with arbitrary perturbations....
Matching stationary spacetimes (2008)
Mena, Filipe C., Natario, Jose
Using the quasi-Maxwell formalism, we derive the necessary and sufficient conditions for the matching of two stationary spacetimes along a stationary timelike hypersurface, expressed in terms of the...
Avoiding closed timelike curves with a collapsing rotating null dust shell (2007)
Mena, Filipe C., Natario, Jose, Tod, Paul
We present an idealised model of gravitational collapse, describing a collapsing rotating cylindrical shell of null dust in flat space, with the metric of a spinning cosmic string as the exterior. We...
Gravitational Collapse to Toroidal and Higher Genus asymptotically AdS Black Holes (2007)
Mena, Filipe C., Natario, Jose, Tod, Paul
We match collapsing inhomogeneous as well as spatially homogeneous but anisotropic spacetimes to vacuum static exteriors with a negative cosmological constant and planar or hyperbolic symmetry. The...
Linear perturbations of matched spacetimes: the gauge problem and background symmetries (2007)
Mars, Marc, Mena, Filipe C., Vera, Raul
We present a critical review about the study of linear perturbations of matched spacetimes including gauge problems. We analyse the freedom introduced in the perturbed matching by the presence of...
Non-linear vector perturbations in a contracting universe (2007)
Mena, Filipe C., Mulryne, David J., Tavakol, Reza
A number of scalar field models proposed as alternatives to the standard inflationary scenario involve contracting phases which precede the universe's present phase of expansion. An important...
Lanczos potentials and a definition of gravitational entropy for perturbed FLRW space-times (2007)
We give a prescription for constructing a Lanczos potential for a cosmological model which is a purely gravitational perturbation of a Friedman-Lemaitre-Robertson-Walker space-time. For the radiation...
We study the matching of LRS spatially homogeneous collapsing dust space-times with non-stationary vacuum exteriors in cylindrical symmetry. Given an interior with diagonal metric we prove existence...
The role of anisotropy and inhomogeneity in Lemaitre-Tolman-Bondi collapse (2004)
Mena, Filipe C., Nolan, Brien C., Tavakol, Reza
We study the effects of shear and density inhomogeneities in the formation of naked singularities in spherically symmetric dust space--times. We find that in general neither of these physical...
Generalisations of the Einstein-Straus model to cylindrically symmetric settings (2004)
Mena, Filipe C., Tavakol, Reza, Vera, Raul
We study generalisations of the Einstein--Straus model in cylindrically symmetric settings by considering the matching of a static space-time to a non-static spatially homogeneous space-time,...
Spherically symmetric perfect fluid in area-radial coordinates (2004)
Iguchi, Hideo, Harada, Tomohiro, Mena, Filipe C
We study the spherically symmetric collapse of a perfect fluid using area-radial coordinates. We show that analytic mass functions describe a static regular centre in these coordinates. In this case,...
Generalisation of the Einstein-Straus model to anisotropic settings (2002)
Mena, Filipe C., Tavakol, Reza, Vera, Raül
We study the possibility of generalising the Einstein--Straus model to anisotropic settings, by considering the matching of locally cylindrically symmetric static regions to the set of $G_4$ on $S_3$...
Geometry and topology of singularities in spherical dust collapse (2002)
Nolan, Brien C., Mena, Filipe C.
We derive some more results on the nature of the singularities arising in the collapse of inhomogeneous dust spheres. (i) It is shown that there are future-pointing radial and non-radial time-like...
Nolan, Brien C., Mena, Filipe C.
It has been claimed that the Lemaitre-Tolman-Bondi-de Sitter solution always admits future-pointing radial time-like geodesics emerging from the shell-focussing singularity, regardless of the nature...
Non-radial null geodesics in spherical dust collapse (2001)
Mena, Filipe C, Nolan, Brien C
The issue of the local visibility of the shell-focussing singularity in marginally bound spherical dust collapse is considered from the point of view of the existence of future-directed null...
Cosmic no-hair: non-linear asymptotic stability of de Sitter universe (2001)
Bruni, Marco, Mena, Filipe C., Tavakol, Reza
We study the asymptotic stability of de Sitter spacetime with respect to non-linear perturbations, by considering second order perturbations of a flat Robertson-Walker universe with dust and a...
Initial data and spherical dust collapse (2000)
Mena, Filipe C., Tavakol, Reza, Joshi, Pankaj S.
By considering families of radial null geodesics, we study the subsets of initial data that lead to naked singularities and black holes in inhomogeneous spherical dust collapse. We introduce the...
Evolution of the density contrast in inhomogeneous dust models (1998)
Mena, Filipe C., Tavakol, Reza
With the help of families of density contrast indicators, we study the tendency of gravitational systems to become increasingly lumpy with time. Depending upon their domain of definition, these...