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f ( R ) theories.

De Felice, Antonio, Tsujikawa, Shinji (2010)

Living Reviews in Relativity [electronic only]

Fastest curves and toroidal black holes

E. Woolgar (1997)

Banach Center Publications

We discuss an apparent paradox (and conjectured resolution) of Jacobson and Venkataramani concerning 'temporarily toroidal' black hole horizons, in light of a recent connectivity theorem for spaces of complete causal curves. We do this in a self-contained manner by first reviewing the 'fastest curve argument' which proves this connectivity theorem, and we note that active topological censorship can be derived as a corollary of this argument. We argue that the apparent paradox arises only when one...

Foliations of lightlike hypersurfaces and their physical interpretation

Krishan Duggal (2012)

Open Mathematics

This paper deals with a family of lightlike (null) hypersurfaces (H u) of a Lorentzian manifold M such that each null normal vector ℓ of H u is not entirely in H u, but, is defined in some open subset of M around H u. Although the family (H u) is not unique, we show, subject to some reasonable condition(s), that the involved induced objects are independent of the choice of (H u) once evaluated at u = constant. We use (n+1)-splitting Lorentzian manifold to obtain a normalization of ℓ and a well-defined...

Formulazione intrinseca del problema di Cauchy in relatività generale

Giorgio Ferrarese (1988)

Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti Lincei. Matematica e Applicazioni

Viene stabilita una formulazione intrinseca del problema di Cauchy in Relatività generale, per uno spazio-tempo riemanniano descritto da un mezzo continuo globale e non-polare. In termini di variabili proprie: metrica, velocità angolare e di deformazione, densità di pura materia, flusso termico e temperatura. Vengono altresì precisate le condizioni iniziali per i dati di Cauchy su una assegnata superficie spaziale σ 3 ; condizioni in involuzione nel senso d'E. Cartan, le quali mettono in evidenza,...

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