40 research outputs found
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 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 . 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 () 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 . 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