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Roberts, M D
The dimensional reduction of eleven dimensional supergravity is discussed. It is shown that there is no dimensional reduction onto RobertsonWalker space with the asymmetric tensorF giving a realistic fluid. Furthermore it is shown that the ansatz’s for the scale factorR:R=at^{n}, R=a exp (bt^{n}), andR=aZ^{n}, there is no dimensional reduction except the known example of the FreundRubinEnglert solution.
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By
Avakyan, R. M.; Haroutunyan, G. H.
1 Citations
The recently discovered accelerated expansion of the universe is of current interest in theoretical research on the evolution of the universe. The cause of this behavior is presumably the presence of dark energy, which has been estimated to form up to 70% of the universe and generates a “repulsive force.” In this paper a cosmological model is constructed which takes the dark energy into account in a JordanBransDicke tensorscalar model with a dominant, nonminimally coupled scalar field in the presence of a cosmological scalar. The radiation dominant epoch is discussed.
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By
Joshi, P S; Narlikar, J V
2 Citations
The usual definition of a black hole is modified to make it applicable in a globally hyperbolic spacetime. It is shown that in a closed globally hyperbolic universe the surface area of a black hole must eventually decrease. The implications of this breakdown of the black hole area theorem are discussed in the context of thermodynamics and cosmology. A modified definition of surface gravity is also given for nonstationary universes. The limitations of these concepts are illustrated by the explicit example of the KerrVaidya metric.
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By
Kembhavi, A K
3 Citations
It is shown that in the framework of a conformally invariant gravitation theory, the singularity which is present in some anisotropic universes in general relativity is due to a wrong choice of conformal frame. Frames exist in which these models can be made singularity free.
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By
Grachev, S. I.
A new method is proposed to account for multiple scattering by electrons in calculations of the correlation functions describing the angular fluctuations in the cosmic microwave background radiation (CMBR). The apparatus of the theory of radiative transport with Rayleigh scattering is used. The problem is reduced to solving an integral equation for the vector source function (dependent only on time), along with differential equations for the other quantities (scalar potentials, baryon velocities, etc.) which show up in the problem. The quantities which describe the angular fluctuations in the CMBR (in the temperature and in the polarization) are then calculated by integrating the vector source function along the line of sight. As an illustration, the correlation functions and power spectra are calculated for the case where the fluctuations are produced by some initial gaussian perturbations of the CMBR.
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By
Vaidya, P C; Patel, L K
11 Citations
Spatially homogeneous spacetimes of Bianchi type IX are considered. A general scheme for the derivation of exact solutions of Einstein’s equations corresponding to perfect fluid plus pure radiation fields is outlined. Some simple rotating Bianchi type IX cosmological models are presented. The details of these solutions are also discussed.
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By
Singh, J P; Prasad, A; Tiwari, R K
1 Citations
Some of the RobertsonWalker cosmological models filled with a fluid with bulk viscosity have been derived which are consistent with causal thermodynamics. The models are discussed briefly.
By
Maharana, Jnanadeva; Mukherji, Sudipta
In this review, we discuss various cosmological issues related to our Universe from a string theoretic perspective. We analyse the prebig bang cosmological scenario which appears naturally in this context due to the existence of scale factor duality symmetry in string theory. We then discuss some of the attractive and problematic features of this scenario. Finally, we introduce a method which is powerful enough to search for cosmological solutions in various low energy limits of string theories.
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By
Banerjee, A; Sanyal, Abhik Kumar; Chakraborty, Subenoy
124 Citations
Some cosmological solutions of massive strings are obtained in Bianchi I spacetime following the techniques used by Letelier and Stachel. A class of solutions corresponds to string cosmology associated with/without a magnetic field and the other class consists of pure massive strings, obeying the Takabayashi equation of stateρ=(1+W)λ.
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By
Seshadri, T. R.
1 Citations
The historical motivation for the BransDicke theory and its connection with Mach’s principle has been discussed. Some examples of actions which can be reduced to the BransDicke type have been given. Further, the recent developments in the theory in the context of inflationary cosmology have been briefly pointed out.
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