Remarks on the Entropy of Non-Stationary Black Holes

The definition of entropy obtained for stationary black holes is extended in this paper to the case of non-stationary black holes. Entropy is defined as a macroscopical thermodynamical quantity which satisfies the first principle of thermodynamics. In the non-stationary case a volume term appears since the solution does not admit a Killing vector

A non-geodesic motion in the R^-1 theory of gravity tuned with observations

In the general picture of high order theories of gravity, recently, the R^-1 theory has been analyzed in two different frameworks. In this letter a third context is added, considering an explicit coupling between the R^-1 function of the Ricci scalar and the matter Lagrangian. The result is a non-geodesic motion of test particles which, in principle, could be connected with Dark Matter and Pioneer anomaly problems.Comment: Accepted for Modern Physics Letters

Hoffmann-Infeld Black Hole Solutions in Lovelock Gravity

Five-dimensional black holes are studied in Lovelock gravity coupled to Hoffmann-Infeld non-linear electrodynamics. It is shown that some of these solutions present a double peak behavior of the temperature as a function of the horizon radius. This feature implies that the evaporation process, though drastic for a period, leads to an eternal black hole remnant. Moreover, the form of the caloric curve corresponds to the existence of a plateau in the evaporation rate, which implies that black holes of intermediate scales turn out to be unstable. The geometrical aspects, such as the absence of conical singularity, the structure of horizons, etc. are also discussed. In particular, solutions that are asymptotically AdS arise for special choices of the parameters, corresponding to charged solutions of five-dimensional Chern-Simons gravity.Comment: 6 pages, 5 figures, Revtex4. References added and comments clarified; version accepted for publicatio

Dark Energy Dominance and Cosmic Acceleration in First Order Formalism

The current accelerated universe could be produced by modified gravitational dynamics as it can be seen in particular in its Palatini formulation. We analyze here a specific non-linear gravity-scalar system in the first order Palatini formalism which leads to a FRW cosmology different from the purely metric one. It is shown that the emerging FRW cosmology may lead either to an effective quintessence phase (cosmic speed-up) or to an effective phantom phase. Moreover, the already known gravity assisted dark energy dominance occurs also in the first order formalism. Finally, it is shown that a dynamical theory able to resolve the cosmological constant problem exists also in this formalism, in close parallel with the standard metric formulation.Comment: 21 pages, LaTeX file, no figures. Replaced version to be published on Phys. Rev.

One-loop f(R) gravity in de Sitter universe

Motivated by the dark energy issue, the one-loop quantization approach for a family of relativistic cosmological theories is discussed in some detail. Specifically, general $f(R)$ gravity at the one-loop level in a de Sitter universe is investigated, extending a similar program developed for the case of pure Einstein gravity. Using generalized zeta regularization, the one-loop effective action is explicitly obtained off-shell, what allows to study in detail the possibility of (de)stabilization of the de Sitter background by quantum effects. The one-loop effective action maybe useful also for the study of constant curvature black hole nucleation rate and it provides the plausible way of resolving the cosmological constant problem.Comment: 25 pages, Latex file. Discussion enlarged, new references added. Version accepted in JCA

f(R)f(R) gravity constrained by PPN parameters and stochastic background of gravitational waves

We analyze seven different viable $f(R)$-gravities towards the Solar System tests and stochastic gravitational waves background. The aim is to achieve experimental bounds for the theory at local and cosmological scales in order to select models capable of addressing the accelerating cosmological expansion without cosmological constant but evading the weak field constraints. Beside large scale structure and galactic dynamics, these bounds can be considered complimentary in order to select self-consistent theories of gravity working at the infrared limit. It is demonstrated that seven viable $f(R)$-gravities under consideration not only satisfy the local tests, but additionally, pass the above PPN-and stochastic gravitational waves bounds for large classes of parameters.Comment: 23 pages, 8 figure

Non-minimal kinetic coupling and Chaplygin gas cosmology

In the frame of the scalar field model with non minimal kinetic coupling to gravity, we study the cosmological solutions of the Chaplygin gas model of dark energy. By appropriately restricting the potential, we found the scalar field, the potential and coupling giving rise to the Chaplygin gas solution. Extensions to the generalized and modified Chaplygin gas have been made.Comment: 18 pages, 2 figures. To appear in EPJ

Entre tentativas reglamentarias y sirvientes organizados: la regulación municipal del servicio doméstico. Ciudad de Buenos Aires, 1875-1912

Este artículo analiza una serie de intentos de regulación municipal del servicio doméstico en la ciudad de Buenos Aires a fines del siglo XIX y principios del XX. Como correlato de estos procesos, reconstruye una serie de experiencias organizativas de los y las trabajadoras del sector que permiten comprender mejor esos marcos regulatorios. Procura demostrar que la regulación del servicio doméstico respondió a un universo de problemas, asociados al crecimiento y las transformaciones de la ciudad. Trabaja con ordenanzas y reglamentos publicados en los digestos municipales, proyectos presentados y tratados en las sesiones ordinarias del Consejo Deliberante, prensa obrera y magazines ilustrados, entre otros documentos de época.This article analyses a series of attempted municipal regulations of domestic work in the City of Buenos Aires in the late nineteenth and early twentieth centuries. In parallel to these processes, this study reconstructs the organizing experiences of domestic workers, which shade light on those regulatory frameworks. The article shows that domestic service regulation responded to a broad range of issues associated with the growth and transformation of the city. It examines laws and regulations published in municipal law digests, projects presented at the regular meetings of the City Council of Buenos Aires, workers’ press, and illustrated magazines, among others documents from the period.Cet article analyse une série de tentatives de régulation municipale du service domestique dans la ville de Buenos Aires à la fin du XIXe siècle et au début du XXe siècle. Corrélativement à ces processus, une série d’expériences d’organisation des travailleurs et des travailleuses est reconstituée pour mieux saisir ce cadre normatif et réglementaire. L’article montre alors que la régulation du service domestique répond à un univers de problèmes associés à la croissance et aux transformations de la ville. Les sources utilisées sont des ordonnances et des règlements publiés dans les digests municipaux, des projets qui furent présentés et traités lors des sessions ordinaires du Conseil Délibératif, la presse ouvrière, des magazines illustrés entre autres documents de l’époque

Revised spherically symmetric solutions of R+ε/RR+\varepsilon/R gravity

We study spherically symmetric static empty space solutions in $R+\varepsilon/R$ model of $f(R)$ gravity. We show that the Schwarzschild metric is an exact solution of the resulted field equations and consequently there are general solutions which {are perturbed Schwarzschild metric and viable for solar system. Our results for large scale contains a logarithmic term with a coefficient producing a repulsive gravity force which is in agreement with the positive acceleration of the universe.Comment: 8 page