We explore the possibility of describing our universe with a singularity-free, closed, spatially homogeneous and isotropic cosmological model, using only general relativity and a suitable equation of state which produces an inflationary era. A phase transition to a radiation-dominated era occurs as a consequence of boundary conditions expressing the assumption that the temperature cannot exceed the Planck value. We find that over a broad range of initial conditions, the predicted value of the Hubble parameter is approximately 47 km s-1 Mpc-1. Inflation is driven by a scalar field, which must be conformally coupled to the curvature if the Einstein equivalence principle has to be satisfied. The form of the scalar field potential is derived, instead of being assumed a priori.


The momentum 4-vector imparted by gravitational waves in Bianchi-type metrics
Havare, A; Korunur, M; Salti, M (Springer Science and Business Media LLC, 2006-01-01)
Considering the MOller, Weinberg and Qadir-Sharif's definitions in general relativity, we find the momentum 4-vector of the closed universe based on the Bianchi-type metrics. The momentum 4-vector (due to matter plus fields) is found to be zero. This result supports the viewpoints of Albrow and Tryon and extends the previous works by Cooperstock-Israelit, Rosen, Johri et al., Banerjee-Sen and Vargas who investigated the problem of the energy in Friedmann-Robertson-Walker universe and SaltI-Havare who studie...
Superposition of FLRW universes
GÜRSES, METİN; Heydarzade, Yaghoub; Tekin, Bayram (IOP Publishing, 2020-06-01)
We show that (1) the Einstein field equations with a perfect fluid source admit a nonlinear superposition of two distinct homogenous Friedman-Lemaitre-Robertson-Walker (FLRW) metrics as a solution, (2) the superposed solution is an inhomogeneous geometry in general, (3) it reduces to a homogeneous one in the two asymptotes which are the early and the late stages of the universe as described by two different FLRW metrics, (4) the solution possesses a scale factor inversion symmetry and (5) the solution impli...
Gravitational energy-momentum density in Bianchi type II space-times
Aydogdu, Oktay (World Scientific Pub Co Pte Lt, 2006-04-01)
In this paper, using Einstein, Landau and Lifshitz's energy-momentum complexes both in general relativity and teleparallel gravity, we calculate the total energy distribution (due to matter and fields, including gravitation) associated with locally rotationally symmetric (LRS) Bianchi type II cosmological models. We show that energy densities in these different gravitation theories are the same, so they agree with each other. We obtain the result that the total energy is zero. This result agrees with previo...
Energy-momentum of a stationary beam of light in teleparallel gravity
Aydogdu, Oktay; Salti, Mustafa (Springer Science and Business Media LLC, 2006-01-01)
In this paper, we utilize the teleparallel gravity analogs of the energy and momentum definitions of Bergmann-Thomson and Landau-Lifshitz in order to explicitly evaluate the energy distribution (due to matter and fields including gravity) based on the Bormor space-time, it is shown that for a stationary beam of light, these energy-momentum definitions give the same result. Furthermore, this result supports the viewpoint of Cooperstock and also agree with the previous works by Bringley and Gad.
An open inflationary model for dimensional reduction and its effects on the observable parameters of the universe
Karaca, K; Bayin, S (World Scientific Pub Co Pte Lt, 2005-04-30)
Assuming that higher dimensions existed in the early stages of the universe where the evolution was inflationary, we construct an open, singularity-free, spatially homogeneous and isotropic cosmological model to study the effects of dimensional reduction that may have taken place during the early stages of the universe. We consider dimensional reduction to take place in a stepwise manner and interpret each step as a phase transition. By imposing suitable boundary conditions we trace their effects on the pre...
Citation Formats
S. BAYIN, F. COOPERSTOCK, and V. FARAONI, “A SINGULARITY-FREE COSMOLOGICAL MODEL WITH A CONFORMALLY COUPLED SCALAR FIELD,” ASTROPHYSICAL JOURNAL, pp. 439–446, 1994, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/66525.