Teleparallel gravity is a gauge theory for the translation group defined in the tangent bundle of a Riemannian spacetime, where the so-called tetrad plays the role of the dynamical field of the theory and is parallely transported (absolute parallelism condition) by assuming the Weitzenböck connection instead of the Levi-Civita connection, leading to a non-null torsion but a null scalar curvature. Whereas teleparallel gravity is equivalent to general relativity, its extensions, also known as f(T) gravities in analogy to f(R) gravity, give rise to new features and interesting properties but are not equivalent to f(R) gravity. In this talk, I will review some of the last analysis about f(T) gravity, including the violation of the local Lorentz invariance, the construction of conformal invariant actions or the non-existence of extra gravitational wave modes, among other issues.
In this talk, I will introduce a method for studying the perception of Hawking radiation by different observers outside a black hole, and for different vacuum states of the radiation field. The analysis is performed in terms of an effective-temperature function that varies along the trajectory of each observer. With this tool, I will show that not all observers crossing the horizon of a black hole in free-fall will fail to detect radiation, and that indeed it is not necessary to strictly form an horizon for obtaining Hawking radiation. Also, the radiation temperature perceived by a generic observer following an arbitrary radial trajectory outside the black hole (when it is possible to talk about a temperature) can be calculated directly from the local characteristics of its trajectory, in a way which has a clear physical interpretation. Finally, our results also point to a self-consistent buoyancy scenario near black holes, due to Hawking radiation.
I will give a pedagogical review of Metric-Affine theories of Gravity (MAG), theories for which the metric and the affine connection are independent quantities (namely in the Palatini approach) and whose actions include covariant derivatives of the matter fields, with the covariant derivative naturally defined using the independent connection. MAG straightforwardly admit the presence of direct couplings involving matter and connection. I will summarize some physical consequences of such theories.
The description of extreme-mass-ratio binary systems is a challenging problem in gravitational wave physics with significant relevance for the future space interferometer eLISA/NGO. The main difficulty lies in the evaluation of the effects of the small body's gravitational field on itself. To that end, an accurate computation of the perturbations produced by the small body with respect to the background geometry of the large object (a massive black-hole) is required. After a presentation of the theoretical perturbative framework for EMRIs, I will present a numerical procedure to generate EMRI wave-forms and compute the self-force in the Regge-Wheeler gauge.
The mass of a black hole has traditionally been identified with its energy. We describe a new perspective on black hole thermodynamics, one that identifies the mass of a black hole with chemical enthalpy, and the cosmological constant as thermodynamic pressure. This leads to an understanding of black holes from the viewpoint of chemistry, in terms of concepts such as Van der Waals fluids, reentrant phase transitions, triple points, and isolated critical point. Both charged and rotating black holes exhibit novel chemical-type phase behaviour, hitherto unseen.