41 citations · 162 across the 14 of their papers we have counts for
14 papers
Anisotropic Generalization of the ΛCDM Universe Model with Application to the Hubble Tension
Øyvind G. Grøn
I deduce an exact and analytic Bianchi type I solution of Einsteins field equations, which generalizes the isotropic LambdaCDM universe model to a corresponding model with anisotro…
Observational Status of Tachyon Natural Inflation and Reheating
Narges Rashidi, Kourosh Nozari, Oyvind Gron
We study observational viability of Natural Inflation with a tachyon field as inflaton. By obtaining the main perturbation parameters in this model, we perform a numerical analysis…
Relativistic Viscous Universe Models
Iver Brevik, Øyvind Grøn
The research on relativistic universe models with viscous fluids is reviewed. Viscosity may have been of significance during the early inflationary era, and may also be of importan…
A source of the C-metric with perfect translational inertial dragging
Brynjar Arnfinnsson, Øyvind Grøn
A new source of the C-metric is described using Israel's formalism. This source is a singular accelerated shell. By construction, perfect inertial dragging is realized inside the s…
Universe Models with Negative Bulk Viscosity
Iver Brevik, Øyvind Grøn
The concept of negative temperatures has occasionally been used in connection with quantum systems. A recent example of this sort is reported in the paper of S. Braun et al. [Scien…
Bianchi Type-I Universe Models with Nonlinear Viscosity
Nouraddin Mostafapoor, Oyvind Gron
In this paper we study the evolution of spatially homogeneous and anisotropic Bianchi type-I Universe models with the cosmological constant, Λ, and filled with nonlinear viscous fl…
A river model of space
S. Braeck, O. Gron
Within the theory of general relativity gravitational phenomena are usually attributed to the curvature of four-dimensional spacetime. In this context we are often confronted with…
A spacetime with closed timelike geodesics everywhere
Oyvind Gron, Steinar Johannesen
In the present article we find a new class of solutions of Einstein's field equations. It describes stationary, cylindrically symmetric spacetimes with closed timelike geodesics ev…
The twin paradox and the principle of relativity
Oyvind Gron
In the standard formulation of the twin paradox an accelerated twin considers himself as at rest and his brother as moving. Hence, when formulating the twin paradox, one uses the g…
FRW Universe Models in Conformally Flat Spacetime Coordinates
Oyvind Gron, Steinar Johannesen
The 3-space of a universe model is defined at a certain simultaneity. Hence space depends on which time is used. We find a general formula generating all known transformations to c…
Optics in a field of gravity
E. Eriksen, O. Gron
An observer at rest in a uniformly accelerated reference frame experiences a parallel gravitational field, where the rays of light are formed as circular arcs instead of being stra…
Singular shell embedded into a cosmological model
Oyvind Gron, Peter D. Rippis
We generalize Israel's formalism to cover singular shells embedded in a non-vacuum Universe. That is, we deduce the relativistic equation of motion for a thin shell embedded in a S…
Gravitational Entropy and Quantum Cosmology
O. Gron, S. Hervik
We investigate the evolution of different measures of ``Gravitational Entropy'' in Bianchi type I and Lemaître-Tolman universe models. A new quantity behaving in accordance with th…
Experimental limits to the density of dark matter in the solar system
Øyvind Grøn, Harald H. Soleng
On the scales of galaxies and beyond there is evidence for unseen dark matter. In this paper we find the experimental limits to the density of dark matter bound in the solar system…