On sign-changeable interaction in FLRW cosmology

We investigate an interacting two-fluid model in a spatially flat Friedmann-Lema\^itre-Robertson-Walker (FLRW) Universe, when the energy transfer between these two dark components is produced by a factorisable nonlinear sign-changeable interaction depending linearly on the energy density and quadratically on the deceleration parameter. We solve the source equation and obtain the effective energy densities of the dark sector and their components. We show that the effective equation of state of the dark sector includes some of the several kind of Chaplygin gas equations of state as well as a generalization of the polytropic equation of state. We use bayesian statistics methods to constrain free parameters in the models during its most recent evolution considering supernovae type Ia and measurements of the Hubble expansion rate. The resulting constraints provide new information on sign-changeable interactions, its equivalences and compatibility with previous models and novel late time universe dynamics.Comment: 8 figure

Análisis del sistema de salud chileno y su estructura en la participación social

The political-economic development that Chile has had in recent decades has allowed the evolution of its health institutions, where hospital coverage, management and infrastructure have been improved. The organization of health policy is highly centralized and structured from the State, this has allowed the rapid implementation of various programs. Participation, on the other hand, is maintained within the spaces that the institutionality allows, however, there is permanent pressure from non-governmental groups that ask for a different governance. Therefore, it is desired to move from a participatory reactivity in health matters to a permanent proactivity, although this requires a permanent conversation between the State and the citizenry. The article analyzes the Chilean health system and how it relates to subsequent citizen participation, highlighting the elements that, under the current social reality, need a change to adequately satisfy the population.El desarrollo político-económico que ha tenido Chile durante las últimas décadas ha permitido la evolución de su institucionalidad sanitaria, donde se ha mejorado la cobertura, gestión e infraestructura hospitalaria. La organización de la política sanitaria es altamente centralizada y estructurada desde el Estado, ello ha permitido implementar con rapidez diversos programas. La participación, por otro lado, se mantiene dentro de los espacios que la institucionalidad permite, sin embargo, existe una permanente presión de grupos no gubernamentales que piden una gobernanza diferente. Se desea, por lo tanto, pasar de una reactividad participativa en materias sanitarias a una proactividad permanente, aunque ello requiere de una permanente conversación entre el Estado y la ciudadanía. En el artículo se analiza el sistema sanitario chileno y cómo se relaciona con la participación ciudadana subsecuente, evidenciando los elementos, que bajo la realidad social actual, necesitan de un cambio para satisfacer adecuadamente a la población

Relic gravitons and viscous cosmologies

Previously it was shown that there exists a class of viscous cosmological models which violate the dominant energy condition for a limited amount of time after which they are smoothly connected to the ordinary radiation era (which preserves the dominant energy conditions). This violation of the dominant energy condition at an early cosmological epoch may influence the slopes of energy spectra of relic gravitons that might be of experimental relevance. However, the bulk viscosity coefficient of these cosmologies became negative during the ordinary radiation era, and then the entropy of the sources driving the geometry decreases with time. We show that in the presence of viscous sources with a linear barotropic equation of state $p=\gamma \rho$ we get viscous cosmological models with positive bulk viscous stress during all their evolution, and hence the matter entropy increases with the expansion time. In other words, in the framework of viscous cosmologies, there exist isotropic models compatible with the standard second law of thermodynamics which also may influence the slopes of energy spectra of relic gravitons.Comment: 5 pages, 4 figure

Interacting cosmic fluids in power-law Friedmann-Robertson-Walker cosmological models

We provide a detailed description for power--law scaling Friedmann-Robertson-Walker cosmological scenarios dominated by two interacting perfect fluid components during the expansion. As a consequence of the mutual interaction between the two fluids, neither component is conserved separately and the energy densities are proportional to $1/t^{2}$. It is shown that in flat FRW cosmological models there can exist interacting superpositions of two perfect fluids (each of them having a positive energy density) which accelerate the expansion of the universe. In this family there also exist flat power law cosmological scenarios where one of the fluids may have a ``cosmological constant" or "vacuum energy" equation of state ($p =-\rho$) interacting with the other component; this scenario exactly mimics the behavior of the standard flat Friedmann solution for a single fluid with a barotropic equation of state. These possibilities of combining interacting perfect fluids do not exist for the non-interacting mixtures of two perfect cosmic fluids, where the general solution for the scale factor is not described by power--law expressions and has a more complicated behavior. In this study is considered also the associated single fluid model interpretation for the interaction between two fluids.Comment: 10 pages. Accepted for publication in Physics Letters

Interacting Kasner-type cosmologies

It is well known that Kasner-type cosmologies provide a useful framework for analyzing the three-dimensional anisotropic expansion because of the simplification of the anisotropic dynamics. In this paper relativistic multi-fluid Kasner-type scenarios are studied. We first consider the general case of a superposition of two ideal cosmic fluids, as well as the particular cases of non-interacting and interacting ones, by introducing a phenomenological coupling function $q(t)$. For two-fluid cosmological scenarios there exist only cosmological scaling solutions, while for three-fluid configurations there exist not only cosmological scaling ones, but also more general solutions. In the case of triply interacting cosmic fluids we can have energy transfer from two fluids to a third one, or energy transfer from one cosmic fluid to the other two. It is shown that by requiring the positivity of energy densities there always is a matter component which violates the dominant energy condition in this kind of anisotropic cosmological scenarios.Comment: Accepted for publication in Astrophysics &Space Science, 8 page