1,045 research outputs found
Comment on "The Cosmic Time in Terms of the Redshift", by Carmeli et al
The time-redshift relation of Carmeli et al. differs from that of the
standard flat LambdaCDM model by more than 500 million years for 1 < z < 4.5.Comment: 2 pages, to appear Found. Phys. Let
Alignment and algebraically special tensors in Lorentzian geometry
We develop a dimension-independent theory of alignment in Lorentzian
geometry, and apply it to the tensor classification problem for the Weyl and
Ricci tensors. First, we show that the alignment condition is equivalent to the
PND equation. In 4D, this recovers the usual Petrov types. For higher
dimensions, we prove that, in general, a Weyl tensor does not possess aligned
directions. We then go on to describe a number of additional algebraic types
for the various alignment configurations. For the case of second-order
symmetric (Ricci) tensors, we perform the classification by considering the
geometric properties of the corresponding alignment variety.Comment: 19 pages. Revised presentatio
Two-dimensional metric and tetrad gravities as constrained second order systems
Using the Gitman-Lyakhovich-Tyutin generalization of the Ostrogradsky method
for analyzing singular systems, we consider the Hamiltonian formulation of
metric and tetrad gravities in two-dimensional Riemannian spacetime treating
them as constrained higher-derivative theories. The algebraic structure of the
Poisson brackets of the constraints and the corresponding gauge transformations
are investigated in both cases.Comment: replaced with revised version published in
Mod.Phys.Lett.A22:17-28,200
5D gravitational waves from complexified black rings
In this paper we construct and briefly study the 5D time-dependent solutions
of general relativity obtained via double analytic continuation of the black
hole (Myers-Perry) and of the black ring solutions with a double
(Pomeransky-Senkov) and a single rotation (Emparan-Reall). The new solutions
take the form of a generalized Einstein-Rosen cosmology representing
gravitational waves propagating in a closed universe. In this context the
rotation parameters of the rings can be interpreted as the extra wave
polarizations, while it is interesting to state that the waves obtained from
Myers-Perry Black holes exhibit an extra boost-rotational symmetry in higher
dimensions which signals their better behavior at null infinity. The analogue
to the C-energy is analyzed.Comment: 18 pages, 4 figures. References added, introduction and conclusions
are amended, some issues related to singularity structure and symmetries are
discussed. Matches the print version to appear in JHE
Yang-Mills Inspired Solutions for General Relativity
Several exact, cylindrically symmetric solutions to Einstein's vacuum
equations are given. These solutions were found using the connection between
Yang-Mills theory and general relativity. Taking known solutions of the
Yang-Mills equations (e.g. the topological BPS monopole solutions) it is
possible to construct exact solutions to the general relativistic field
equations. Although the general relativistic solutions were found starting from
known solutions of Yang-Mills theory they have different physical
characteristics.Comment: 13 pages LaTe
Position and momentum observables on R and on R^3
We characterize all position and momentum observables on R and on R^3. We
study some of their operational properties and discuss their covariant joint
observables.Comment: 18 page
General covariance violation and the gravitational dark matter. I. Scalar graviton
The violation of the general covariance is proposed as a resource of the
gravitational dark matter. The minimal violation of the covariance to the
unimodular one is associated with the massive scalar graviton as the simplest
representative of such a matter. The Lagrangian formalism for the continuous
medium, the perfect fluid in particular, in the scalar graviton environment is
developed. The implications for cosmology are shortly indicated.Comment: 11 pages; minor correction
On Hamiltonian formulation of the Einstein-Hilbert action in two dimensions
It is shown that the well-known triviality of the Einstein field equations in
two dimensions is not a sufficient condition for the Einstein-Hilbert action to
be a total divergence, if the general covariance is to be preserved, that is, a
coordinate system is not fixed. Consequently, a Hamiltonian formulation is
possible without any modification of the two dimensional Einstein-Hilbert
action. We find the resulting constraints and the corresponding gauge
transfromations of the metric tensor.Comment: 9 page
Serum levels of matrix metalloproteinases-2 and-9 and their tissue inhibitors in inflammatory neuromuscular disorders
We monitored serum levels of matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) before and during intravenously applied immunoglobulin (IVIG) therapy in 33 patients with chronic immune-mediated neuropathies and myopathies and 15 controls. Baseline MMP-2 and TIMP-2 serum levels were lower and MMP-9 and TIMP-1 serum levels higher in all patients compared to age-matched controls. Eight days after IVIG treatment, MMP-2, TIMP-2, and TIMP-1 serum levels increased, while MMP-9 serum levels decreased, indicating tissue repair. After 60 days, MMP-9 levels increased, MMP-2 approached normal levels, while TIMP-1 and TIMP-2 serum levels were below day 8 levels, indicating relapsing tissue damage. Comparing the MMP/TIMP results with the clinical courses, IVIG treatment tended to change MMP/TIMP levels in a way that paralleled clinical improvement and relapse. In sum, during a distinct time period, IVIG therapy seems to be able to modulate VIMP-mediated tissue repair. Copyright (c) 2006 S. Karger AG, Basel
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