Cosmic acceleration with a positive cosmological constant

Arbab, Arbab I.

doi:10.1088/0264-9381/20/1/307

Cited by 61 publications

(41 citation statements)

References 16 publications

(23 reference statements)

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“…Al-Rawaf and Taha (1996) and Al-Rawaf (1998) and Overduin and Cooperstock (1998) have proposed a cosmological model with a cosmological constant of the form = βÄ A , where β is a constant. Following the same decay law recently Arbab (2003aArbab ( , 2003b has investigated cosmic acceleration with positive cosmological constant and analyze the implication of a model builtin cosmological constant. One of the motivations for introducing term is to reconcile the age parameter and the density parameter of the universe with recent observational data.…”

Section: Introductionmentioning

confidence: 97%

Five dimensional universe model with variable cosmological term Λ and a big bounce

Khadekar

Kamdi

Pradhan³

et al. 2007

Astrophys Space Sci

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We assume the four dimensional induced matter of the 5D Ricci flat bouncing cosmological solution contains a perfect fluid. The big bounce singularity of simple 5D cosmological model is studied with the cosmological term = αρ and = βH 2 where α and β are constants and ρ and H are respectively energy density and Hubble parameter. This big bounce singularity is found to be an event horizon at which the scale factor and mass density of the universe are finite, while the pressure is infinite.

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Section: Introductionmentioning

confidence: 97%

Five dimensional universe model with variable cosmological term Λ and a big bounce

Khadekar

Kamdi

Pradhan³

et al. 2007

Astrophys Space Sci

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“…Of interest for us is the decaying law ∝ a −2 where a(t) is the scale factor of the FRW metric (Chen and Wu 1990). It has been discussed widely by several authors in the literature (Al-Rawaf and Taha 1996; Al-Rawaf 1998; Overdin and Cooperstock 1998;Arbab 2003aArbab , 2003b. By making the assumption that the extra dimensions compactify as the visible dimensions expand, the phenomenological law ∝ a −2 may explain why the effective cosmological constant is reduced from a large value at early times to a sufficiently small value at late times in consistency with the observational upper limit.…”

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confidence: 85%

Accelerated expansion of the universe in a non-trivial extra-dimensional topology

El-Nabulsi

2009

Astrophys Space Sci

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The recent observational available data for an accelerated expansion state of the present universe, obtained from distant SNeIa gave strong support to the search of alternative cosmologies. Recently, there have been a number of different attempts to modify Einstein's gravity to yield accelerated expansion at late times. Unfortunately, many of the theoretical models discussed in the literature are plagued with theoretical problems, in particular the singularity problem at the origin of time. In the present work we have analyzed a multidimensional spacetime Friedmann-RobertsonWalker (FRW) model with a decaying cosmological constant and a varying gravitational constant. Many interesting consequences are revealed, in particular the behavior of the scale factor and the shape of the universe in terms of the number of extra dimensions.Keywords Higher-dimensional cosmology · Decaying lambda · Dark energy · Phantom energy PACS 04.50.+h · 11.25.Yb · 98.80.Es · 95.36.+xThe recent available astronomical observations (around 1998 and 1999) of the dynamics of galaxies, cluster of galaxies, of luminosity distances of the Type Ia supernovae (SNeIa) as a function of redshift with redshift in the range −0.10 ≤ z ≤ 0.83, the first acoustic peak of the CMB temperature fluctuations or anisotropies and also the observational results coming from the cosmic microwave background radiation along with the Maxima and Boomerang data favor a spatially flat matter dominated universe undergoing a phase of accelerated expansion dominated by an unknown form of repulsive energy dubbed "Dark Energy (DE)". This ephemeral dark energy should have a negative pressure and has special effects that have only been detected on the largest scales of our Universe and then only in the past ten years (Riess et al. 1998;Perlmutter et al. 1999;Schmidt et al. 1998;Steinhardt et al. 1999;Persic et al. 1996;Carmeli and Kuzmenko 2002;Behar and Carmeli 2002). Presently, as already mentioned, the universe is accelerating in time with the equation of state (EoS) parameter w = p/ρ < −1/3 (ρ and p are respectively the density and pressure of a perfect fluid). However, for models described by w > −1, the null energy condition T μν k μ k ν > 0 is satisfied (T μν is the stress-energy tensor for all time-like vectors k μ ). In contrast to models with w < −1 (phantom energy), the null energy condition ρ + p < 0 with ρ > 0 is violated. Surprisingly, this case is not excluded by observation.In fact, the observed DE is dominated by some fields that have not yet relaxed to their vacuum state. Questions still linger about the nature of dark matter, especially its distribution in the central region of clusters and galaxies. The nature of the dark energy component responsible for the accelerated expansion of the universe is one of the most profound problems in high energy physics. On the other hand the results of large-scale structure surveys and the results of measurements of the masses of galaxies give a best fit for the density parameter for matter of m,0 = 0.3 and consequently ...

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“…For example, the relations Λ ∝ H 2 , Λ ∝ qH 2 [45], and Λ ∝ ǫ m [46] give the same cosmological evolution [44]. Since the decay law Λ ∝ H 2 appears to be inconsistent with current constraints on the dark energy equation of state [16,43], so do the other equivalent models.…”

Section: The Interaction Between Matter and Dark Energymentioning

confidence: 99%

Interacting dark energy inf(R)gravity

Popławski

2006

Phys. Rev. D

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The field equations in f (R) gravity derived from the Palatini variational principle and formulated in the Einstein conformal frame yield a cosmological term which varies with time. Moreover, they break the conservation of the energy-momentum tensor for matter, generating the interaction between matter and dark energy. Unlike phenomenological models of interacting dark energy, f (R) gravity derives such an interaction from a covariant Lagrangian which is a function of a relativistically invariant quantity (the curvature scalar R). We derive the expressions for the quantities describing this interaction in terms of an arbitrary function f (R), and examine how the simplest phenomenological models of a variable cosmological constant are related to f (R) gravity. Particularly, we show that Λc 2 = H 2 (1 − 2q) for a flat, homogeneous and isotropic, pressureless universe. For the Lagrangian of form R − 1/R, which is the simplest way of introducing current cosmic acceleration in f (R) gravity, the predicted matter-dark energy interaction rate changes significantly in time, and its current value is relatively weak (on the order of 1% of H0), in agreement with astronomical observations. PACS numbers: 04.50.+h, 95.36.+x, 98.80.-k

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Cosmic acceleration with a positive cosmological constant

Cited by 61 publications

References 16 publications

Five dimensional universe model with variable cosmological term Λ and a big bounce

Five dimensional universe model with variable cosmological term Λ and a big bounce

Accelerated expansion of the universe in a non-trivial extra-dimensional topology

Interacting dark energy inf(R)gravity

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