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Isotropic evolution of a JBD anisotropic Bianchi universe

H. N. Núñez-Yépez
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Abstract

I study the dynamical effects due to the Brans-Dicke scalar $ϕ$-field at the early stages of a supposedly anisotropic Universe expansion in the scalar-tensor cosmology of Jordan-Brans-Dicke. This is done considering the behaviour of the general solutions for the homogeneous model of Bianchi type VII in the vacuum case. I conclude that the Bianchi-VII$_0$ model shows an isotropic expansion and that its only physical solution is equivalent to a Friedman-Robertson-Walker spacetime whose evolution can, depending on the value of the JBD coupling constant, begin in a singularity and, after expanding (inflating, if $ω>0$), shrink to another, or starting in a non-singular state, collapse to a singularity. I also conclude that the general Bianchi-VII$_h$ (with $h\neq 0$) models show strong curvature singularities producing a complete collapse of the homogeinity surfaces to 2D-manifolds, to 1D-manifolds or to single points. Our analysis depends crucially on the introduction of the so-called intrinsic time, $Φ$, as the product of the JBD scalar field $ϕ$ times a mean scale factor $a^3=a_1a_2a_3$, in which the finite-cosmological-time evolution of this universe unfolds into an infinite $Φ$-range. These universes isotropize from an anisotropic initial state, thence I conclude that they are stable against anisotropic perturbations.

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H. N. Núñez-Yépez. 2001-09-05. Isotropic evolution of a JBD anisotropic Bianchi universe. https://doi.org/10.1023/a%3A1013027201473

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