318 research outputs found
The kinetic gas universe
A description of many-particle systems, which is more fundamental than the
fluid approach, is to consider them as a kinetic gas. In this approach the
dynamical variable in which the properties of the system are encoded, is the
distribution of the gas particles in position and velocity space, called
1-particle distribution function (1PDF). However, when the gravitational field
of a kinetic gas is derived via the Einstein-Vlasov equations, the information
about the velocity distribution of the gas particles is averaged out and
therefore lost. We propose to derive the gravitational field of a kinetic gas
directly from its 1PDF, taking the velocity distribution fully into account. We
conjecture that this refined approach could possibly account for the observed
dark energy phenomenology.Comment: 4 pages, Essay written for the Gravity Research Foundation
competition 2020, Journal references update
On the gauge fixing in the Hamiltonian analysis of general teleparallel theories
The covariant formulation of teleparallel gravity theories must include the
spin connection, which has 6 degrees of freedom. One can, however, always
choose a gauge such that the spin connection is put to zero. In principle this
gauge may affect counting of degrees of freedom in the Hamiltonian analysis. We
show for general teleparallel theories of gravity, that fixing the gauge such
that the spin connection vanishes in fact does not affect the counting of
degrees of freedom. This manifests in the fact that the momenta of the Lorentz
transformations which generate the spin connection are fully determined by the
momenta of the tetrads.Comment: 8 pages, no figures, Contribution to the proceedings of the
conference "Teleparallel Universes" in Salamanc
Are implants more reliable than severely compromised endodontically treated teeth as abutments for zirconia-based FPDs?
Dissertation im Rahmen einer Publikationspromotion zum Thema: Are implants more reliable than severely compromised endodontically treated teeth as abutments for zirconia-based FPDs?:Inhaltsverzeichnis
1. Ableitung der Rationalen und Einführung in die Thematik
1.1. Ableitung der Rationalen
1.2. Erfolgsprognosen von endodontisch behandelten Zähnen
1.3. Ferrule und dentale Stifte
1.4. Implantate im Frontzahnbereich
1.5. Vergleich endodontisch behandelter Zahn und Implantat
1.6. Anteriore Versorgungen mit festsitzendem Zahnersatz
1.7. Wissenschaftliche Aktualität der Studie
2. Publikation
3. Zusammenfassung der Arbeit
4. Literaturverzeichnis
5. Darstellung und Spezifikation des eigenen wissenschaftlichen Beitrages zur Publikation
6. Erklärung über die eigenständige Abfassung der Arbeit
7. Anlagen
7.1. Abkürzungsverzeichni
Flat connection for rotating vacuum spacetimes in extended teleparallel gravity theories
Teleparallel geometry utilizes Weitzenb\"ock connection which has nontrivial
torsion but no curvature and does not directly follow from the metric like
Levi-Civita connection. In extended teleparallel theories, for instance in
or scalar-torsion gravity, the connection must obey its antisymmetric
field equations. So far only a few analytic solutions were known. In this note
we solve the gravity antisymmetric vacuum field equations for a
generic rotating tetrad ansatz in Weyl canonical coordinates, and find the
corresponding spin connection coefficients. By a coordinate transformation we
present the solution also in Boyer-Lindquist coordinates, often used to study
rotating solutions in general relativity. The result hints for the existence of
another branch of rotating solutions besides the Kerr family in extended
teleparallel gravities.Comment: minor clarifications and references added; 14 pages, no figures;
contributed to the special issue "Selected Papers from Teleparallel Universes
in Salamanca 2018
Geodesics and the magnitude-redshift relation on cosmologically symmetric Finsler spacetimes
We discuss the geodesic motion of both massive test particles, following timelike geodesics, and light, following null geodesics, on Finsler spacetimes with cosmological symmetry. Using adapted coordinates on the tangent bundle of the spacetime manifold, we derive the general form of the geodesic equation. Further, we derive a complete set of constants of motion. As an application of these findings, we derive the magnitude-redshift relation for light propagating on a cosmologically symmetric Finsler background, both for a general Finsler spacetime and for particular examples, such as spacetimes equipped with Bogoslovsky and Randers length measures. Our results allow a confrontation of these geometries with observations of the magnitude and redshift of supernovae. © 2017 American Physical Society
Teleparallel axions and cosmology
We consider the most general teleparallel theory of gravity whose action is a
linear combination of the five scalar invariants which are quadratic in the
torsion tensor. Since two of these invariants possess odd parity, they
naturally allow for a coupling to pseudo-scalar fields, thus yielding a
Lagrangian which is even under parity transformations. In analogy to similar
fields in gauge theories, we call these pseudo-scalar fields \emph{teleparallel
axions}. For the most general coupling of a single axion field, we derive the
cosmological field equations. We find that for a family of cosmologically
symmetric teleparallel geometries, which possess non-vanishing axial torsion,
the axion coupling contributes to the cosmological dynamics in the early
universe. Most remarkably, this contribution is also present when the axion is
coupled to the teleparallel equivalent of general relativity, hence allowing
for a canonical coupling of a pseudo-scalar to general relativity. For this
case we schematically present the influence of the axion coupling on the fixed
points in the cosmological dynamics understood as dynamical system. Finally, we
display possible generalizations and similar extensions in other geometric
frameworks to model gravity.Comment: 16 page
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