A new special class of Petrov type D vacuum space-times in dimension five

Using extensions of the Newman-Penrose and Geroch-Held-Penrose formalisms to five dimensions, we invariantly classify all Petrov type $D$ vacuum solutions for which the Riemann tensor is isotropic in a plane orthogonal to a pair of Weyl alligned null directionsComment: 4 pages, 1 table, no figures. Contribution to the proceedings of the Spanish Relativity Meeting 2010 held in Granada (Spain

Isocausal spacetimes may have different causal boundaries

We construct an example which shows that two isocausal spacetimes, in the sense introduced by Garc\'ia-Parrado and Senovilla, may have c-boundaries which are not equal (more precisely, not equivalent, as no bijection between the completions can preserve all the binary relations induced by causality). This example also suggests that isocausality can be useful for the understanding and computation of the c-boundary.Comment: Minor modifications, including the title, which matches now with the published version. 12 pages, 3 figure

Causal symmetries

Based on the recent work \cite{PII} we put forward a new type of transformation for Lorentzian manifolds characterized by mapping every causal future-directed vector onto a causal future-directed vector. The set of all such transformations, which we call causal symmetries, has the structure of a submonoid which contains as its maximal subgroup the set of conformal transformations. We find the necessary and sufficient conditions for a vector field \xiv to be the infinitesimal generator of a one-parameter submonoid of pure causal symmetries. We speculate about possible applications to gravitation theory by means of some relevant examples.Comment: LaTeX2e file with CQG templates. 8 pages and no figures. Submitted to Classical and Quantum gravit

Spinor calculus on 5-dimensional spacetimes

Penrose's spinor calculus of 4-dimensional Lorentzian geometry is extended to the case of 5-dimensional Lorentzian geometry. Such fruitful ideas in Penrose's spinor calculus as the spin covariant derivative, the curvature spinors or the definition of the spin coefficients on a spin frame can be carried over to the spinor calculus in 5-dimensional Lorentzian geometry. The algebraic and differential properties of the curvature spinors are studied in detail and as an application we extend the well-known 4-dimensional Newman-Penrose formalism to a 5-dimensional spacetime.Comment: Convention mismatch and minor typos fixed. To appear in Journal of Mathematical Physic

Computability of the causal boundary by using isocausality

Recently, a new viewpoint on the classical c-boundary in Mathematical Relativity has been developed, the relations of this boundary with the conformal one and other classical boundaries have been analyzed, and its computation in some classes of spacetimes, as the standard stationary ones, has been carried out. In the present paper, we consider the notion of isocausality given by Garc\'ia-Parrado and Senovilla, and introduce a framework to carry out isocausal comparisons with standard stationary spacetimes. As a consequence, the qualitative behavior of the c-boundary (at the three levels: point set, chronology and topology) of a wide class of spacetimes, is obtained.Comment: 44 pages, 5 Figures, latex. Version with minor changes and the inclusion of Figure

A Note on Non-compact Cauchy surface

It is shown that if a space-time has non-compact Cauchy surface, then its topological, differentiable, and causal structure are completely determined by a class of compact subsets of its Cauchy surface. Since causal structure determines its topological, differentiable, and conformal structure of space-time, this gives a natural way to encode the corresponding structures into its Cauchy surface

Grain-size trends associated with sediment transport patterns in Cadiz Bay (southwest Iberian Peninsula)

En la zona infralitoral y de plataforma interna, las tendencias en los parámetros granulométricos permiten caracterizar ambientes antiguos y modernos, e identificar trayectorias de transporte de sedimentos mediante el análisis de las distribuciones granulométricas y el análisis factorial multivariante. En la bahía de Cádiz, las tendencias observadas en los parámetros granulométricos están controladas por los aportes de sedimentos finos, la configuración de la costa y las trayectorias de transporte en suspensión debidas a las corrientes de reflujo mareal. La asimetría es el parámetro principal en la identificación de tendencias granulométricas. Se han determinado tres tendencias que caracterizan los ambientes sedimentarios presentes: a) asimetrías muy positivas y distribuciones muy leptocúrticas indican un alto grado de madurez textural y retrabajamiento; b) tendencias hacia asimetrías negativas caracterizan ambientes intermareales de playa y permiten localizar ambientes paleolitorales; c) distribuciones simétricas y mal seleccionadas trazan las trayectorias permanentes de precipitación de sedimentos finos, mientras asimetrías más positivas, aumento del tamaño de grano y mejor selección marcan la extensión ocasional de las plumas de materia en suspensión.On the inner continental shelf and coastal environments, grain-size trends make it possible to characterise ancient and modern environments, and to identify net sediment transport patterns, using grain-size distributions and factorial multivariate analysis. In Cadiz Bay, grain-size trends are controlled by the contribution of fine sediments, coastal morphology and the suspended transport pathways due to the ebb-currents. The main parameter able to identify grain-size trends is skewness. Three trends were determined to characterise present-day sedimentary environments: a) very positively skewed sediments with leptokurtic distributions belong to deposits with a high degree of textural maturity and reworking; b) negatively skewed sediments characterise intertidal environments (foreshore), and also make it possible to localise palaeolittoral environments; c) symmetrical and poorly sorted distributions indicate the permanent fine-settling pathways, whereas positively skewed, coarser and better-sorted sediments point to the occasional extension of suspended matter plumes.Instituto Español de Oceanografí

On the causal properties of warped product spacetimes

It is shown that the warped product spacetime P=M *_f H, where H is a complete Riemannian manifold, and the original spacetime M share necessarily the same causality properties, the only exceptions being the properties of causal continuity and causal simplicity which present some subtleties. For instance, it is shown that if diamH=+\infty, the direct product spacetime P=M*H is causally simple if and only if (M,g) is causally simple, the Lorentzian distance on M is continuous and any two causally related events at finite distance are connected by a maximizing geodesic. Similar conditions are found for the causal continuity property. Some new results concerning the behavior of the Lorentzian distance on distinguishing, causally continuous, and causally simple spacetimes are obtained. Finally, a formula which gives the Lorentzian distance on the direct product in terms of the distances on the two factors (M,g) and (H,h) is obtained.Comment: 22 pages, 2 figures, uses the package psfra