20,616 research outputs found
CCDM Model with Spatial Curvature and The Breaking of "Dark Degeneracy"
Creation of Cold Dark Matter (CCDM), in the context of Einstein Field
Equations, leads to a negative creation pressure, which can be used to explain
the accelerated expansion of the Universe. Recently, it has been shown that the
dynamics of expansion of such models can not be distinguished from the
concordance CDM model, even at higher orders in the evolution of
density perturbations, leading at the so called "dark degeneracy". However,
depending on the form of the CDM creation rate, the inclusion of spatial
curvature leads to a different behavior of CCDM when compared to CDM,
even at background level. With a simple form for the creation rate, namely,
, we show that this model can be distinguished from
CDM, provided the Universe has some amount of spatial curvature.
Observationally, however, the current limits on spatial flatness from CMB
indicate that neither of the models are significantly favored against the other
by current data, at least in the background level.Comment: 13 pages, 5 figure
3D simulations of Einstein's equations: symmetric hyperbolicity, live gauges and dynamic control of the constraints
We present three-dimensional simulations of Einstein equations implementing a
symmetric hyperbolic system of equations with dynamical lapse. The numerical
implementation makes use of techniques that guarantee linear numerical
stability for the associated initial-boundary value problem. The code is first
tested with a gauge wave solution, where rather larger amplitudes and for
significantly longer times are obtained with respect to other state of the art
implementations. Additionally, by minimizing a suitably defined energy for the
constraints in terms of free constraint-functions in the formulation one can
dynamically single out preferred values of these functions for the problem at
hand. We apply the technique to fully three-dimensional simulations of a
stationary black hole spacetime with excision of the singularity, considerably
extending the lifetime of the simulations.Comment: 21 pages. To appear in PR
Multifragmentation of non-spherical nuclei
The shape influence of decaying thermalized source on various characteristics
of multifragmentation as well as its interplay with effects of angular momentum
and collective expansion are first studied and the most pertinent variables are
proposed. The analysis is based on the extension of the statistical
microcanonical multifragmentation model.Comment: 5 pages, 4 figure
Foliation, jet bundle and quantization of Einstein gravity
In \cite{Park:2014tia} we proposed a way of quantizing gravity with the
Hamiltonian and Lagrangian analyses in the ADM setup. One of the key
observations was that the physical configuration space of the 4D
Einstein-Hilbert action admits a three-dimensional description, thereby making
gravity renormalization possible through a metric field redefinition.
Subsequently, a more mathematical and complementary picture of the reduction
based on foliation theory was presented in \cite{Park:2014qoa}. With the setup
of foliation the physical degrees of freedom have been identified with a
certain leaf. Here we expand the work of \cite{Park:2014qoa} by adding another
mathematical ingredient - an element of jet bundle theory. With the
introduction of the jet bundle, the procedure of identifying the true degrees
of freedom outlined therein is made precise and the whole picture of the
reduction is put on firm mathematical ground.Comment: 34 pages, 3 figures, sections restructured and two appendices added,
comments on loop quantum gravity added, refs added, version to appear in
Frontiers in Physic
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