Behavior of cosmological models with varying<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>G</mml:mi></mml:math>

Barrow, John D.; Parsons, Paul

doi:10.1103/physrevd.55.1906

Cited by 133 publications

(176 citation statements)

References 73 publications

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“…It is because although the change of gravitational constant is possible in the matter dominated era following the radiation dominated era it is restricted by the nucleosyntheis analysis. Up to back in nucleosynthesis era, only a small variation of the gravitational constant from the presently observed value of G 0 is found to be consistent with the observed primordial abundance [14].…”

supporting

confidence: 59%

Thermodynamic constraint on primordial black hole formation in the radiation dominated epoch

Lee

2002

Phys. Rev. D

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It has been suggested that the overdense region as a result of inhomogeneities in the early Universe would have undergone a collapse into the primordial black holes (PBH). In this work, we discuss a possible constraint on the PBH formation in the radiation dominated epoch by imposing the generalized second law of thermodynamics in the context of spherically collapsing scenario. It is found that both the critical temperature Tc over which the formation of PBH is not possible and the lower bound on the mass of PBH depend on the number of degrees of freedom at the time of PBH formation. In the standard model, one can show that the lower bound on the mass of PBH known in the literature, of order Planck mass, is consistent with the thermodynamic constraint constructed in this work. We also pointed out the possibility that the critical temperature(lower bound on PBH mass) can be lowered(increased) provided the number of relativistic degrees of freedom of the Universe is increasing substantially beyond the standard model.There are many observational indications , for example, the existence of the galaxies and the fluctuations observed in CMBR, which imply that the early Universe must have been inhomogeneous. It has been suggested that the overdense region as a result of inhomogeneities in the early Universe underwent into the primordial black holes(PBH). The existence of PBH has been considered to have interesting cosmological consequences, for example, on the cosmic microwave background radiation, primordial nucleosynthesis and dark matter candidate. The mass distribution of PBH can provide a useful information on the spectrum of density fluctuations in the early Universe. Hence the formation as well as the evolution of PBH have been interesting subjects of investigations [3] [4] [5]. Since PBH is an issue in the early Universe, the discussion depends on the theory of gravity, which might be different from that of Einstein. For example, the formation and evolution of PBH has been discussed also in scalar-tensor theories of gravity [15].One of the remarkable developments in black hole physics is the thermodynamic understanding of a black hole [6] [7]. The entropy of a black hole is proportional to the surface area of horizon and the temperature to the surface gravity. Then the second law of thermodynamics can be stated in a generalized way that the total entropy of black hole plus external Universe never decreases. Hence it is interesting to see whether the generalized second law of thermodynamics can impose any constraint on the physical processes in which black holes are involved. The purpose of this work is to discuss how the formation of PBH can be constrained by imposing the generalized second law of thermodynamics, which is believed to be valid during the spherically collapsing process.The evolution of the overdense gravity-dominated-regions is supposed to be described by the Friedman-RobertsonWalker(FRW) metric. Since overdense region is characterized with the spatial curvature, k > 0, in the background of expan...

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supporting

confidence: 59%

Thermodynamic constraint on primordial black hole formation in the radiation dominated epoch

Lee

2002

Phys. Rev. D

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“…Throughout the paper, will denote the usual smooth (connected, Hausdorff, 4-dimensional) spacetime manifold with smooth Lorentz metric of signature (− + + +) (see for example [23] In each of the studied cases we will get restrictions on the constants ( ) 3 =1 We define the deceleration parameter as…”

Section: Self-similar Solutionsmentioning

confidence: 99%

“…Since the pioneers works by Dirac, who considered the possibility of a variable G (see [1]), there have been numerous modifications of general relativity to allow for variable G and Λ (see for example [2] and [3]) Recent observations [4][5][6] suggest us that the Universe is expanding in an accelerating way and that such acceleration is governed by a positive dynamical cosmological constant. A summary of these models with time dependent cosmological "constant" is given by Overduin and Cooperstock [7], another review of interest is given by Amendola and Tsu-jikawa [8] in the framework of dark energy model.…”

Section: Introductionmentioning

confidence: 99%

Bianchi I in scalar and scalar-tensor cosmologies

Belinchón

2012

Open Physics

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Abstract:We study how the constants G and Λ may vary in different theoretical models (general relativity (GR) with a perfect fluid, scalar cosmological models (SM) ("quintessence") with and without interacting scalar and matter fields and three scalar-tensor theories (STT) with a dynamical Λ) in order to explain some observational results. We apply the program outlined in section II to study the Bianchi I models, under the self-similarity hypothesis. We put special emphasis on calculating exact power-law solutions which allow us to compare the different models. In all the studied cases we conclude that the solutions are isotropic and noninflationary. We also arrive at the conclusion that in the GR model with time-varying constants, Λ vanishes while G is constant. In the SM all the solutions are massless i.e. the potential vanishes and all the interacting models are inconsistent from the thermodynamical point of view. The solutions obtained in the STT collapse to the perfect fluid one obtained in the GR model where G is a true constant and Λ vanishes as in the GR and SM frameworks. PACS

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“…In a more general theory it may be regarded as a function, usually of the BD scalar. We use one of the simple functions, investigated in a cosmological framework, [33,34], namely:…”

Section: General Scalar-tensor Theorymentioning

confidence: 99%

q stars in scalar-tensor gravitational theories in extra dimensions

Prikas

2006

Journal of Mathematical Physics

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We present Jordan-Brans-Dicke and general scalar-tensor gravitational theory in extra dimensions in an asymptotically flat or anti de Sitter spacetime. We consider a special gravitating, boson field configuration, a q-star, in 3, 4, 5 and 6 dimensions, within the framework of the above gravitational theory and find that the parameters of the stable stars are a few per cent different from the case of General Relativity.

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Behavior of cosmological models with varyingG

Cited by 133 publications

References 73 publications

Thermodynamic constraint on primordial black hole formation in the radiation dominated epoch

Thermodynamic constraint on primordial black hole formation in the radiation dominated epoch

Bianchi I in scalar and scalar-tensor cosmologies

q stars in scalar-tensor gravitational theories in extra dimensions

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