Exact-Brans-Dicke-Friedmann-Robertson-Walker-Bianchi-Kantowski-Sachs vacuum solutions

In this paper, we obtain exact cosmological vacuum solutions for an extended FLRW homogenous and isotropic Brans-Dicke (BD) universe in five dimensions for all values of the curvature index. Then, by employing the equations associated to a modified Brans-Dicke theory (MBDT) [1], we construct the physics on a four-dimensional hypersurface. We show that the induced matter obeys the equation of state of a fluid of a barotropic type. We discuss the properties of such an induced matter for some values of the equation of state parameter and analyze in detail their corresponding solutions. To illustrate the cosmological behaviors of the solutions, we contrast our solutions with those present the standard Brans-Dicke theory. We retrieve that, in MBDT scenario, it is impossible to find a physically acceptable solution associated to the negative curvature for both the dustdominated and radiation-dominated universes. However, for a spatially flat and closed universes, we argue that our obtained solutions are more general than those associated to the standard BD theory and, moreover, they contain a few classes of solutions which have no analog in the BD cosmology. For those particular cases, we further compare the results with those extracted in the context of the induced matter theory (IMT) and general relativity (GR). Furthermore, we discuss in detail the time behaviors of the cosmological quantities and compare them with recent observational data. We find a favorable range for the deceleration parameter associated to a matter-dominated spatially flat universe (for the late times) which is compatible with recent corresponding observational results.

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“…Radiation dominated universe in the context of the standard BD theory has been investigated in [17,18,[49][50][51].…”

Section: Radiation Cosmologiesmentioning

confidence: 99%

Exact cosmological solutions in modified Brans–Dicke theory

Rasouli

Moniz

2016

Class. Quantum Grav.

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“…Apparently, the status of the ω = −3/2 case has not been fully cleared out so far. In particular, this case was never expressed in terms of cosmic time instead of parametric (generalized conformal) time, although it was presumably solved in earlier references [28,29,30]. In this context we will then discuss the conformal relativistic solutions of the system (III.5)-(III.7) for ω = −3/2 (see also [31] where β = const.…”

Section: Conformal Friedmann Cosmologymentioning

confidence: 99%

The conformal status of ο = -3/2 Brans-Dicke cosmology

Dąbrowski¹,

Denkiewicz

Blaschke

2007

Ann. Phys.

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Following recent fit of supernovae data to Brans-Dicke theory which favours the model with ω = −3/2 [1] we discuss the status of this special case of Brans-Dicke cosmology in both isotropic and anisotropic framework. It emerges that the limit ω = −3/2 is consistent only with the vacuum field equations and it makes such a Brans-Dicke theory conformally invariant. Then it is an example of the conformal relativity theory which allows the invariance with respect to conformal transformations of the metric. Besides, Brans-Dicke theory with ω = −3/2 gives a border between a standard scalar field model and a ghost/phantom model.In this paper we show that in ω = −3/2 Brans-Dicke theory, i.e., in the conformal relativity there are no isotropic Friedmann solutions of non-zero spatial curvature except for k = −1 case. Further we show that this k = −1 case, after the conformal transformation into the Einstein frame, is just the Milne universe and, as such, it is equivalent to Minkowski spacetime. It generally means that only flat models are fully consistent with the field equations. On the other hand, it is shown explicitly that the anisotropic non-zero spatial curvature models of Kantowski-Sachs type are admissible in ω = −3/2 Brans-Dicke theory. It then seems that an additional scale factor which appears in anisotropic models gives an extra deegre of freedom and makes it less restrictive than in an isotropic Friedmann case.

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“…and ∂ t denotes differentiation with respect to cosmic time, t. The Brans-Dicke field determines the Planck length, Φ = l −2 Pl , and, in string theory, is related to the string scale, l st , by Φ = l −2 st e −φ . The field equations (2.3) may be written as [18]…”

Section: Introductionmentioning

confidence: 99%

Effects of anisotropy and spatial curvature on the pre-big-bang scenario

1998

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A class of exact, anisotropic cosmological solutions to the vacuum BransDicke theory of gravity is considered within the context of the pre-big bang scenario. Included in this class are the Bianchi type III, V and VI h models and the spatially isotropic, negatively curved Friedmann-Robertson-Walker universe. The effects of large anisotropy and spatial curvature are determined. In contrast to negatively curved Friedmann-Robertson-Walker model, there exist regions of the parameter space in which the combined effects of curvature and anisotropy prevent the occurrence of inflation. When inflation is possible, the necessary and sufficient conditions for successful pre-big bang inflation are more stringent than in the isotropic models. The initial state for these models is established and corresponds in general to a gravitational plane wave.

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Exact-Brans-Dicke-Friedmann-Robertson-Walker-Bianchi-Kantowski-Sachs vacuum solutions

Cited by 56 publications

References 49 publications

Exact cosmological solutions in modified Brans–Dicke theory

Exact cosmological solutions in modified Brans–Dicke theory

The conformal status of ο = -3/2 Brans-Dicke cosmology

Effects of anisotropy and spatial curvature on the pre-big-bang scenario

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