Gravitational induced particle production through a nonminimal curvature-matter coupling

We consider the possibility of a gravitationally induced particle production through the mechanism of a nonminimal curvature-matter coupling. An interesting feature of this gravitational theory is that the divergence of the energy-momentum tensor is nonzero. As a first step in our study we reformulate the model in terms of an equivalent scalar-tensor theory, with two arbitrary potentials. By using the formalism of open thermodynamic systems, we interpret the energy balance equations in this gravitational theory from a thermodynamic point of view, as describing irreversible matter creation processes. The particle number creation rates, the creation pressure, and the entropy production rates are explicitly obtained as functions of the scalar field and its potentials, as well as of the matter Lagrangian. The temperature evolution laws of the newly created particles are also obtained. The cosmological implications of the model are briefly investigated, and it is shown that the late-time cosmic acceleration may be due to particle creation processes. Furthermore, it is also shown that due to the curvature--matter coupling, during the cosmological evolution a large amount of comoving entropy is also produced.Comment: 15 pages; accepted for publication in the European Physical Journal

Holographic dark energy in Brans-Dicke theory

In this Letter it is shown that when the holographic dark energy is combined with the Brans-Dicke field equations the transition from decelerated to accelerated expansion of the Universe can be more easily accounted for than when resort to the Einstein field equations is made. Likewise, the coincidence problem of late cosmic acceleration gets more readily softened

Gauge invariance in the presence of a cutoff

We use the method of gauging equations to construct the electromagnetic current operator for the two-nucleon system in a theory with a finite cutoff. The employed formulation ensures that the two-nucleon T-matrix and corresponding five-point function, in the cutoff theory, are identical to the ones formally defined by a reference theory without a cutoff. A feature of our approach is that it effectively introduces a cutoff into the reference theory in a way that maintains the long-range part of the exchange current operator; for applications to effective field theory (EFT), this property is usually sufficient to guarantee the predictive power of the resulting cutoff theory. In addition, our approach leads to Ward-Takahashi (WT) identities that are linear in the interactions. From the point of view of EFT's where such a WT identity is satisfied in the reference theory, this ensures that gauge invariance in the cutoff theory is maintained order by order in the expansion.Comment: 15 pages, 2 figure

The role of cardiorespiratory fitness on the risk of sudden cardiac death at the population level: A systematic review and meta-analysis of the available evidence

Cardiorespiratory fitness (CRF) has been widely studied as a powerful and independent predictor of all-cause and disease-specific mortality. Sudden cardiac death (SCD) is recognized as a significant cause of mortality among the general population, including the general population without previous symptoms of any coronary heart disease (CHD). Consequently, SCD is an important public health problem, which constitutes a clinical challenge. Thus, prevention of SCD by detecting early risk factors could be a useful tool, contributing to the American Heart Association‘s goal of decreasing the incidence of SCD at the population level. The identification of these risk factors for CVD would facilitate the large-scale screening of those participants at higher risk of SCD. This systematic review collects information about the role of CRF on the risk of SCD at the available evidence, and analyzes the long-term influence of CRF as a risk factor and independent predictor of SCD

Big rip avoidance via black holes production

We consider a cosmological scenario in which the expansion of the Universe is dominated by phantom dark energy and black holes which condense out of the latter component. The mass of black holes decreases via Hawking evaporation and by accretion of phantom fluid but new black holes arise continuously whence the overall evolution can be rather complex. We study the corresponding dynamical system to unravel this evolution and single out scenarios where the big rip singularity does not occur.Comment: 16 pages, two figures. Key words. Cosmology, phantom energy, black holes. Sligthly extended version to be published in Gravitation and Cosmolog

Aportaciones al conocimiento de las comunidades de Pistacia Terenbinthus L. y de Acer Monspessulanum L. en el Sur de la Península Ibérica

Se aportan nuevos datos fitosociológicos sobre los terebintales-cornicabrales béticos, con la propuesta de una nueva asociación (Phillyreo latifoliae-Pistacietum terebinthi ass. nova) que representa a las formaciones de microfanerófitos mediterráneos perennifolios integrados en Quercetalia ilicis pero dominados por algunas especies caducifolias como Pistacia terebinthus. Se define también una nueva subasociación de los quejigares bético-torcalenses (Vinco difformis-Quercetum fagineae aceretosum monspessulani subass. nova) cuyo significado fitocenológico corresponde a un enriquecimiento en especies eurosiberianas y submediterráneas de Quercetalia pubescentis, fundamentalmente debido a un incremento en la altitud y a causa de las condiciones microclimáticas del biotopo en el que se asienta dicha comunidad.Contribution to the noules of the comunities of Pistacia terebinthus and Acer monspessulanum in Southern Iberian Peninsula. New phytosociological data about winter-deciduous pistachio tree forest (Phillyreo latifoliae-Pistacietum terebinthi ass. nova) endemic of the Betica province and Mediterranean region are presented. This new association is formed quantitatively by an evergreen forest; however there might predominate deciduous species such as Pistacia terebinthus. In addition, we propose a new subassociation of maple forest into the Torcalense phytogeographical subsector (Vinco difformis-Quercetum fagineae aceretosum monspessulani subass. nova). This subassociation develops on higher areas with north exposition. These conditions enable eurosiberian and submediterranean species, which belong to the phytosociological order of Quercetalia pubescentis

Las comunidades escionitrófilas de Alliaria petiolata (M. Bieb.) Cavara & Grande en el sur de la Península Ibérica

Las comunidades caracterizadas por Alliaria petiolata en el sur de la Península Ibérica corresponden a la asociación Myrrhoidi nodosae-Alliarietum petiolatae (clase Galio-Urticetea). Dicha asociación presenta su óptimo en la Sierra de Ayllón (Provincia Carpetano-Ibérico-Leonesa), e irradia hacia el suroeste por los sistemas béticos (provincia corológica Bética), cambiando su composición florística y empobreciéndose en esa dirección, siguiendo los distintos sectores fitogeográficos. Estos aspectos son reflejados fielmente por tres subasociaciones y una variante: subass. smyrnietosum perfoliati (subsectores Cazorlense y Alcaracense), subass. nepetosum granatensis (sectores Nevadense y Almijaro-Granatense) y subass. ranunculetosum blepharicarpi comb. nova (subsector Torcalense), que llega de modo finícola como variante supramediterránea con Sysimbrium crassifolium al extremo suroeste de las cordilleras (sector Rondeño). Esta distribución manifiesta una vía migratoria para taxones y sintaxones orófilos y mesófilos por las montañas béticas. Además, Alliaria petiolata, por su propia autoecología, su cortejo florístico y el hábitat que precisa, es un fiel bioindicador de bosques caducifolios, riparios y de abetos, que se pueden considerar hoy día muy singulares por su carácter relicto, submediterráneo o por habitar condiciones ecológicas especiales.Plant communities with Alliaria petiolata (M. Bieb.) Cavara & Grande in the South of the Iberian Peninsula. Plant communities characterized by Alliaria petiolata in the south of de Iberian Peninsula can be included in Myrrhoidi nodosae-Alliarietum petiolatae association (Galio-Urticetea class). This association is located in Ayllon mountains (Carpetano-Ibérico-Leonesa province) and distributed towards the southwest by the Betic mountain ranges (Betic chorological province) varying its floristic composition as the association reaches the different phytogeographical sectors. These aspects are clearly defined by three subassociations and one variant: subass. smyrnietosum perfoliati (Cazorlense and Alcaracense subsectors), subass. nepetosum granatensis (Nevadense y and Almijaro-Granatense sectors) and subass. ranunculetosum blepharicarpi comb. nova (Torcalense subsector) that reaches the southwest limit of Betic ranges as a supramediterranean variant with Sisymbrium crassifolium (Rondeño sector). This distribution may indicate a migratory route for orophyllous and mesophyllous taxa and syntaxa throughout the Betic Mountains. Moreover, Alliaria petiolata is an accurate bioindicator for the undergrowth of deciduous, riparian and mixed Abies pinsapo forests considered actually remarkable because of its relict character, sub-Mediterranean phytogeographical position, or special ecological requirements

Sobre las alisedas nevadenses (Sierra Nevada, Granada-Almería, España)

Se ha realizado un estudio fitosociológico sobre las alisedas (bosques de Alnus glutinosa) en Sierra Nevada (Granada-Almería, España). Para ello, se han recopilado los datos existentes en archivos históricos y en bibliografía, además de reunir inventarios bibliográficos e inventarios propios. La distribución conocida de las alisedas en Sierra Nevada está centrada en dos zonas: en la cara sur los barrancos de Poqueira y Trevélez (Granada) y en la cara norte los afluentes del río Alhama de Lugros (Granada). También existen en la Sierra Nevada almeriense (río Andarax). Tras un análisis detallado de las tablas fitosociológicas, de su fitoecología, composición florística, distribución y estructura, llegamos a la conclusión de que las alisedas de Sierra Nevada constituyen una nueva asociación que denominamos Carici camposii-Alnetum glutinosae ass. nova. Se trata de bosques caducifolios muy desarrollados, con estrato arbóreo, arbustivo y herbáceo, que se desarrollan en tramos riparios con agua permanente, sobre materiales silíceos, en el piso supramediterráneo del sector fitogeográfico Nevadense (provincia Bética). Existe una variante que habita laderas de gran inclinación con suelos rezumantes, donde las alisedas muestran mayor biomasa (altura, cobertura) y aparecen algunas especies fitoindicadoras (Geum urbanum). El análisis de la tabla sintética muestra su clara separación del resto de alisedas sur-ibéricas de Osmundo-Alnion, destacando la ausencia del bioindicador más característico de esa alianza (Osmunda regalis) en la nueva asociación.Alnus glutinosa forests in Sierra Nevada (Granada-Almeria, Spain). A phytosociological survey has been made on Alnus glutinosa forests in Sierra Nevada. Historical and bibliographical data have been compiled as well as published and new phytosociological inventories. The known distribution of Alnus glutinosa forests in Sierra Nevada is concentrated in two main zones: in the southern slope along the rivers Poqueira and Trevélez (Granada) and in the northern slope along the tributaries of the Alhama de Lugros river (Granada). They have been also inventoried in Almeria province (Andarax river). After detailed analysis of phytosociological inventories and tables as well as for the ecology, floristic composition, distribution and forest structure, we conclude that the A. glutinosa forests of Sierra Nevada represent a new association: Carici camposii-Alnetum glutinosae ass. nova. They are well developed forest with trees, shrubs, and grasses strata, appearing in river banks with permanent streams, on siliceous soils in the supramediterranean bioclimatic belt of the Nevadense phytogeographical sector (Betic province). A variant, indicated by Geum urbanum, develops in high incline slopes with permanent wet soils where A. glutinosa forests show the greatest biomass (canopy cover and height of trees). Analysis of synthetic table shows clear division from the rest of the Osmundo-Alnion south-Iberian forests, emphasizing the absence of the main indicator of the alliance (Osmunda regalis) in the new association

Dissipative cosmological solutions

The exact general solution to the Einstein equations in a homogeneous Universe with a full causal viscous fluid source for the bulk viscosity index $m=1/2$ is found. We have investigated the asymptotic stability of Friedmann and de Sitter solutions, the former is stable for $m\ge 1/2$ and the latter for $m\le 1/2$. The comparison with results of the truncated theory is made. For $m=1/2$, it was found that families of solutions with extrema no longer remain in the full case, and they are replaced by asymptotically Minkowski evolutions. These solutions are monotonic.Comment: 17 pages, LaTeX 2.09, 1 figure. To be published in Classical and Quantum Gravit