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LRS Bianchi Type-I Inflationary String Cosmological Model in Brans-Dicke Theory of Gravitation

DOI: 10.1155/2014/909374

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We investigate locally rotational symmetric (LRS) Bianchi type I space time coupled with scalar field. String cosmological models generated by a cloud of strings with particles attached to them are studied in the Brans-Dicke theory. We assume that the expansion scalar is proportional to the shear scalar and also power law ansatz for scalar field. The physical behavior of the resulting model is discussed through different parameters. 1. Introduction It is believed that the early universe evolved through some phase transitions, thereby yielding a vacuum energy density which at present is at least 118 orders of magnitudes smaller than in the Planck time [1]. Such a discrepancy between theoretical expectations and empirical observations constitutes a fundamental problem in the interface uniting astrophysics, particle physics, and cosmology. The recent observational evidence for an accelerated state of the present universe, obtained from distant SNe Ia (Perlmutter et al. [2]; Riess et al. [3]), gave strong support to search for alternative cosmologies. Thus, the state of affairs has stimulated the interest in more general models containing an extra component describing dark energy and simultaneously accounting for the present accelerated stage of the universe. The isotropic models are considered to be the most suitable to study large scale structure of the universe. However, it is believed that the early universe may not have been exactly uniform. This prediction motivates us to describe the early stages of the universe with the models having anisotropic background. Thus, it would be worthwhile to explore anisotropic models in the context of modified theories of gravity. Among the various modifications of general relativity (GR), the Brans-Dicke (BD) theory of gravity [4] is a well-known example of a scalar tensor theory in which the gravitational interaction involves a scalar field and the metric tensor. One extra parameter is used in this theory which satisfies the equation given by where is known as BD scalar field while is the trace of the matter energy-momentum tensor. It is mentioned here that the general relativity is recovered in the limiting case . Thus we can compare our results with experimental tests for significantly large value of . The majority of popular cosmological models, including all the ones referred to above, use the cosmological principle; that is, they assume that the universe is homogeneous and isotropic. On the other hand, there are hints in the CMB temperature anisotropy studies that suggest that the assumption of statistical


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