1,284 research outputs found
A Newtonian approach to the cosmological dark fluids
We review the hydrodynamics of the dark sector components in Cosmology. For
this purpose we use the approach of Newtonian gravitational instability, and
thereafter we add corrections to arrive to a full relativistic description. In
Cosmology and Astrophysics, it is usual to decompose the dark sector into two
species, dark matter and dark energy. We will use instead a unified approach by
describing a single unified dark fluid with very simple assumptions, namely the
dark fluid is barotropic and its sound speed vanishes.Comment: 13 pages, To be published in 'Selected Topics of Computational and
Experimental Fluid Mechanics' Springer Book Series: Environmental Science and
Engineering: Environmental Scienc
Productivity of a \u3cem\u3eLeucaena Leucocephala-Cynodon Nlemfuensis\u3c/em\u3e Silvopastoral System with Sheep in Yucatan, Mexico
Animal production in the tropics of Mexico is based on grazed grasslands of low productivity; this type of production system has reduced the areas of natural vegetation and damaged the ecology (erosion of flora, fauna and soil). Silvopastoral technologies may improve the welfare and economic conditions of the rural population and, consequently, preserve their natural resources. The current work was designed to assess the introduction of Leucaena leucocephala in a silvopastoral system with Cynodon nlemfuensis (star grass) grazed by sheep
Constant mean curvature solutions of the Einstein-scalar field constraint equations on asymptotically hyperbolic manifolds
We follow the approach employed by Y. Choquet-Bruhat, J. Isenberg and D.
Pollack in the case of closed manifolds and establish existence and
non-existence results for the Einstein-scalar field constraint equations on
asymptotically hyperbolic manifolds.Comment: 15 page
Probing two approaches to Unified Dark Dynamics
Dark matter and dark energy are essential in the description of the late
Universe, since at least the epoch of equality. On the other hand, the
inflation is also necessary and demands a "dark" component, usually associated
to a scalar field that dominated the dynamics and kinematics in the very early
Universe. Yet, these three dark components of standard model of cosmology are
independent from each other, although there are alternative models that pursue
to achieve a triple unification, or at least a double. In the present work we
present an update of two models that we have considered in recent years. The
first is the "dark fluid" model in which dark matter and dark energy are the
same thing, achieving a double unification with specific properties that
exactly emulate the standard model of cosmology, given the dark degeneracy that
exists in the LCDM model. The second model is given by a single F(X) scalar
field Lagrangian, with which one is able to model the whole cosmological
dynamics, from inflation to today, representing a triple unification model. We
highlight the main properties of these models, as well as we test them against
known cosmological probes.Comment: 20 pages, 5 figures, 1 table. arXiv admin note: substantial text
overlap with arXiv:1108.245
The Ricci flow of asymptotically hyperbolic mass and applications
We consider the evolution of the asymptotically hyperbolic mass under the
curvature-normalized Ricci flow of asymptotically hyperbolic, conformally
compactifiable manifolds. In contrast to asymptotically flat manifolds, for
which ADM mass is constant during Ricci flow, we show that the mass of an
asymptotically hyperbolic manifold of dimension n>2 decays smoothly to zero
exponentially in the flow time. From this, we obtain a no-breathers theorem and
a Ricci flow based, modified proof of the scalar curvature rigidity of
zero-mass asymptotically hyperbolic manifolds. We argue that the nonconstant
time evolution of the asymptotically hyperbolic mass is natural in light of a
conjecture of Horowitz and Myers, and is a test of that conjecture. Finally, we
use a simple parabolic scaling argument to produce a heuristic "derivation" of
the constancy of ADM mass under asymptotically flat Ricci flow, starting from
our decay formula for the asymptotically hyperbolic mass under the
curvature-normalized flow.Comment: Revised in accord with referee comments, typos and minor errors
corrected, Appendix B added, footnotes in-lined; version accepted for
publicatio
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