Abstract: Classical scalar fields have been proposed as possible candidates for the dark matter component of the universe. Given the fact that super-massive black holes seem to exist at the center of most galaxies, in order to be a viable candidate for the dark matter halo a scalar field configuration should be stable in the presence of a central black hole, or at least be able to survive for cosmological time-scales. In the present work we consider a scalar field as a test field on a Schwarzschild background, and study under which conditions one can obtain long-lived configurations. We show that there exist configurations that can remain surrounding a black hole for large time-scales. In particular, ultra-light scalar field dark matter around supermassive black holes can survive for cosmological times.
Abstract: We present a simple isometric embedding of the nonrotating BTZ black hole spacetime into (3+2)-dimensional Minkowski space and (3+1)-dimensional mathematical AdS space. A one parameter family of embeddings of the physical (2+1) AdS space (i.e. the universal covering of AdS) is obtained by a double Wick rotation from the BTZ case.
Abstract: We review the topic of black hole collisions. We will give an overview of what has been done so far in four dimensional vacuum gravity and we expand on our group's recent efforts of performing black hole collisions in asymptotically de Sitter spaces, Einstein-Maxwell theory and higher-dimensional vacuum gravity.
The first meeting of the Numerical Relativity and High Energy Physics Network took place at Aveiro University, from 9-13 July 2012. This meeting brought together researchers from Brazil, Italy, Portugal, Spain and the USA, to discuss the state of the art in relativistic gravity and its application in various contexts, ranging from astrophysics to particle physics, using both anaytical and numerical techniques.
Abstract: We give a brief overview of naked singularities, how these can form from gravitational collapse and their possible relevance in astrophysics. We investigate how the black hole formation process described by the Oppenheimer-Snyder scenario is affected once small pressures are introduced in the collapsing matter cloud.
Abstract: n-DBI gravity is a gravitational theory introduced in arXiv:1109.1468[hep-th], motivated by Dirac-Born-Infeld type conformal scalar theory and designed to yield non-eternal inflation spontaneously. I explain that any solution of Einstein gravity with a particular curvature property is a solution of n-DBI gravity.
Abstract: We make a broad discussion, both mathematical and physical, of different aspects of Palatini theories of gravity. These theories are defined by the idea that metric and connection are physically independent entities, in such a way that the field equations are obtained by performing independent variations with respect to both of them.
In this short course, we review Dirac's method for dealing with constrained systems in the Hamiltonian formalism, including: primary and secondary constraints, first- and second-class constraints, gauge transformations, and counting of degrees of freedom. Examples and exercises, with particular emphasis on gauge field theories (electromagnetism and gravity) will be provided.
Our group coordinated the "Numerical Relativity and High Energy Physics" IRSES network (2012-2015). Here is a list of the global network meetings organized:
