36 research outputs found
A cosmological model in Weyl-Cartan spacetime: I. Field equations and solutions
In this first article of a series on alternative cosmological models we
present an extended version of a cosmological model in Weyl-Cartan spacetime.
The new model can be viewed as a generalization of a model developed earlier
jointly with Tresguerres. Within this model the non-Riemannian quantities, i.e.
torsion and nonmetricity , are proportional to
the Weyl 1-form. The hypermomentum depends on our
ansatz for the nonmetricity and vice versa. We derive the explicit form of the
field equations for different cases and provide solutions for a broad class of
parameters. We demonstrate that it is possible to construct models in which the
non-Riemannian quantities die out with time. We show how our model fits into
the more general framework of metric-affine gravity (MAG).Comment: 22 pages, 2 figures, uses IOP preprint styl
Testing non-standard cosmological models with supernovae
In this work we study the magnitude-redshift relation of a non-standard
cosmological model. The model under consideration was firstly investigated
within a special case of metric-affine gravity (MAG) and was recently recovered
via different approaches by two other groups. Apart from the usual cosmological
parameters for pressure-less matter , cosmological
constant/dark energy , and radiation a new
density parameter emerges. The field equations of the model
reduce to a system which is effectively given by the usual Friedmann equations
of general relativity, supplied by a correction to the energy density and
pressure in form of , which is related to the non-Riemannian
structure of the underlying spacetime. We search for the best-fit parameters by
using recent SN Ia data sets and constrain the possible contribution of a new
dark-energy like component at low redshifts, thereby we put an upper limit on
the presence of non-Riemannian quantities in the late stages of the universe.
In addition the impact of placing the data in redshift bins of variable size is
studied. The numerical results of this work also apply to several anisotropic
cosmological models which, on the level of the field equations, exhibit a
similar scaling behavior of the density parameters like our non-Riemannian
model.Comment: 21 pages, 10 figures, uses IOP preprint style, submitted to Class.
Quantum Gra
A cosmological model in Weyl-Cartan spacetime
We present a cosmological model for early stages of the universe on the basis
of a Weyl-Cartan spacetime. In this model, torsion and
nonmetricity are proportional to the vacuum polarization.
Extending earlier work of one of us (RT), we discuss the behavior of the cosmic
scale factor and the Weyl 1-form in detail. We show how our model fits into the
more general framework of metric-affine gravity (MAG).Comment: 19 pages, 5 figures, typos corrected, uses IOP style fil
Weyssenhoff fluid dynamics in general relativity using a 1+3 covariant approach
The Weyssenhoff fluid is a perfect fluid with spin where the spin of the
matter fields is the source of torsion in an Einstein-Cartan framework. Obukhov
and Korotky showed that this fluid can be described as an effective fluid with
spin in general relativity. A dynamical analysis of such a fluid is performed
in a gauge invariant manner using the 1+3 covariant approach. This yields the
propagation and constraint equations for the set of dynamical variables. A
verification of these equations is performed for the special case of
irrotational flow with zero peculiar acceleration by evolving the constraints.Comment: 20 page
Cosmological applications in Kaluza-Klein theory
The field equations of Kaluza-Klein (KK) theory have been applied in the
domain of cosmology. These equations are solved for a flat universe by taking
the gravitational and the cosmological constants as a function of time t. We
use Taylor's expansion of cosmological function, , up to the first
order of the time . The cosmological parameters are calculated and some
cosmological problems are discussed.Comment: 14 pages Latex, 5 figures, one table. arXiv admin note: text overlap
with arXiv:gr-qc/9805018 and arXiv:astro-ph/980526
Speed of light in the extended gravity theories
We shall investigate the possibility of formulation of varying speed of light
(VSL) in the framework of Palatini non-linear Ricci scalar and Ricci squared
theories. Different speeds of light including the causal structure constant,
electromagnetic, and gravitational wave speeds are discussed. We shall see that
two local frames are distinguishable and discuss about the velocity of light in
these two frames. We shall investigate which one of these local frames is
inertial.Comment: 19 pages. to appear in Classical Quantum Gravit
Measuring the gravitational field in General Relativity: From deviation equations and the gravitational compass to relativistic clock gradiometry
How does one measure the gravitational field? We give explicit answers to
this fundamental question and show how all components of the curvature tensor,
which represents the gravitational field in Einstein's theory of General
Relativity, can be obtained by means of two different methods. The first method
relies on the measuring the accelerations of a suitably prepared set of test
bodies relative to the observer. The second methods utilizes a set of suitably
prepared clocks. The methods discussed here form the basis of relativistic
(clock) gradiometry and are of direct operational relevance for applications in
geodesy.Comment: To appear in "Relativistic Geodesy: Foundations and Application", D.
Puetzfeld et. al. (eds.), Fundamental Theories of Physics, Springer 2018, 52
pages, in print. arXiv admin note: text overlap with arXiv:1804.11106,
arXiv:1511.08465, arXiv:1805.1067
LTB solutions in Newtonian gauge: from strong to weak fields
Lemaitre-Tolman-Bondi (LTB) solutions are used frequently to describe the
collapse or expansion of spherically symmetric inhomogeneous mass distributions
in the Universe. These exact solutions are obtained in the synchronous gauge
where nonlinear dynamics (with respect to the FLRW background) induce large
deviations from the FLRW metric. In this paper we show explicitly that this is
a gauge artefact (for realistic sub-horizon inhomogeneities). We write down the
nonlinear gauge transformation from synchronous to Newtonian gauge for a
general LTB solution using the fact that the peculiar velocities are small. In
the latter gauge we recover the solution in the form of a weakly perturbed FLRW
metric that is assumed in standard cosmology. Furthermore we show how to obtain
the LTB solutions directly in Newtonian gauge and illustrate how the Newtonian
approximation remains valid in the nonlinear regime where cosmological
perturbation theory breaks down. Finally we discuss the implications of our
results for the backreaction scenario.Comment: 17 page
de Sitter Thick Brane Solution in Weyl Geometry
In this paper, we consider a de Sitter thick brane model in a pure geometric
Weyl integrable five-dimensional space-time, which is a generalization of
Riemann geometry and is invariant under a so-called Weyl rescaling. We find a
solution of this model via performing a conformal transformation to map the
Weylian structure into a familiar Riemannian one with a conformal metric. The
metric perturbations of the model are discussed. For gravitational
perturbation, we get the effective modified Pschl-Teller
potential in corresponding Schrdinger equation for
Kaluza-Klein (KK) modes of the graviton. There is only one bound state, which
is a normalizable massless zero mode and represents a stable 4-dimensional
graviton. Furthermore, there exists a mass gap between the massless mode and
continuous KK modes. We also find that the model is stable under the scalar
perturbation in the metric. The correction to the Newtonian potential on the
brane is proportional to , where is the de Sitter
parameter of the brane. This is very different from the correction caused by a
volcano-like effective potential.Comment: 24 pages, 13 figures, published versio
Constraining spacetime torsion with LAGEOS
We compute the corrections to the orbital Lense-Thirring effect (or
frame-dragging) in the presence of spacetime torsion. We derive the equations
of motion of a test body in the gravitational field of a rotating axisymmetric
massive body, using the parametrized framework of Mao, Tegmark, Guth and Cabi.
We calculate the secular variations of the longitudes of the node and of the
pericenter. We also show how the LAser GEOdynamics Satellites (LAGEOS) can be
used to constrain torsion parameters. We report the experimental constraints
obtained using both the nodes and perigee measurements of the orbital
Lense-Thirring effect. This makes LAGEOS and Gravity Probe B (GPB)
complementary frame-dragging and torsion experiments, since they constrain
three different combinations of torsion parameters