Living with phantoms fields in a sheet spacetime

El-Nabulsi, Ahmad Rami

doi:10.1007/s10714-009-0911-x

Cited by 34 publications

(14 citation statements)

References 117 publications

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“…Within the structure of extra dimensions, the decaying of the effective cosmological constant plays a fundamental role (Darabi 2003;Mersini 2001;Koyama 2008). Various ansatzes of the decaying lambda have been explored in cosmology, which exhibit crucial roles in higherdimensional cosmology (El-Nabulsi 2009a, 2009b, 2009c, 2009d and wormhole physics (El-Nabulsi 2009e, 2009f, 2009g). In this work, our main aim is to derive the time dependence of the cosmological constant from the theory itself.…”

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confidence: 99%

Noncommutative accelerated multidimensional universe dominated by quintessence

El-Nabulsi

2010

Astrophys Space Sci

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Noncommutative Geometry recently attracted growing interest of cosmologists, mainly after the greatest success of unifying the forces of nature into a single gravitational spectral action in a purely algebraic way, rather than as being an entirely new formalism. In the present work, we discuss a multidimensional Friedmann-Robertson-Walker flat universe in which the perfect fluid has a Gaussian profile in time and depends on a fundamental minimal length √ θ like ρ = ρ(0) exp(−t 2 /4θ) for some positive constant ρ(0). This special form is motivated by a more recent noncommutative inflationary cosmological model, which was found to be able to drive the universe through a bounce without the need of any scalar field. Furthermore, we conjecture that the generalized equation of state has the special form p = ωa m ρ − ρ, (ω, m) ∈ R where a(t) is the scale factor. It was found that the expansion of the multidimensional universe accelerates in time and is dominated for very large time by quintessence. Many additional consequences are revealed and discussed in some detail.Keywords Noncommutative geometry · Higher-dimensional cosmology · Accelerated expansion · QuintessenceThe recent discovery of the accelerated expansion of the universe based on the CMBR dataset of the Three-Year WMAP observations and results obtained using combined WMAP data and data from Supernova Legacy Survey of type Ia and galaxy ( Schmidt et al. 1998;Steinhardt et al. 1999;Persic et al. 1996;Alcaniz 2004) push the theorists into the belief that standard Hot Big Bang cosmology (HBBC) is not really the complete and successful theory for the description of the evolution of the universe. The HBBC model fails to explain two old problems: the flatness problem and the homogeneity of the universe on large scales. Astronomical observations indicate that the density parameter Ω k = −0.015 +0.020 −0.016 (within a 2% margin of error), i.e. the universe is flat as predicted by inflation theory. The inflationary scenario offers a possible solution to the flatness and homogeneity problems but fails to answer the question "why the cosmos expands in time". Theorists tried to answer this embarrassing question by conjecturing the existence of a mysterious form of dark energy (DE) with negative pressure obeying the equation of state parameter (EoSP) w = −1.06 +0.13 −0.08 (Riess et al. Here w = p/ρ where ρ and p are respectively the density and pressure of the 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 disparity to phantom-dominated models with w < −1, the null energy condition ρ + p < 0 with ρ > 0 is violated. Amazingly, this case is not expelled by astronomical observations. In the previous few years, many different models of DE were explored to fit the CMBR observations as well as LSS observations and observations of supernovae against the background of the accelerated expansion of the universe. Some of the DE are K-essence with mod...

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Noncommutative accelerated multidimensional universe dominated by quintessence

El-Nabulsi

2010

Astrophys Space Sci

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“…5, No. 5;2013 (76) implies in particular 0 < C 3 + C 4 δ < 1 4 , from which we deduce, by sending the first term of r.h.s of (75) to l.h.s that: 3 4…”

Section: Global Existence Of Solutionsmentioning

confidence: 77%

“…5, No. 5;2013 In what follows, [0, T [ , T > 0 is the maximal existence domain of solution E, f of (S 1 ) − (S 2 ) such that…”

Section: The Methodsmentioning

confidence: 99%

“…5, No. 5;2013 in which c (p, q, Ω) is a real-valued function. We prove, by a direct calculation, using (5) to express p 0 , q 0 in terms of p , q and next (25) to express p , q in terms of p, q, that equation (22) leads to a quadratic equation in c, which solves to give the only non trivial solution:…”

Section: The Boltzmann Equation In Fmentioning

confidence: 99%

“…5, No. 5;2013 It is important to notice that on the trajectories, the equation (60) is equivalent to the equation (34) which writes in our situation:…”

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The Galerkin Method for Global Solutions to the Maxwell-Boltzmann System

Ayissi¹,

Noutchegueme²

2013

APR

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We prove an existence and uniqueness of solution to the Maxwell-Boltzmann coupled system globally in time. We first of all describe the background space-time and the unknown functions, making some hypotheses concerning the potentials of gravitation a and b, which determine the gravitational field g, the distribution function f which is unknown and is subject to the Boltzmann equation, as well as the collision kernel σ which appears in the collision operator. We after clarify the choice of the function spaces and we establish step by step, using Sobolev theorems, all the essential energy estimations leading to the global existence theorem. The method used for the investigation of the global existence combine the Galerkin method which is applied in a particular separable Hilbert space which is a Sobolev space with weight, and the standard theory on the first order differential systems. We then give at the end, the physical significance of our work.

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Five-dimensional Brans–Dicke M 1×R 3×S 1 cosmology with chameleon scalar field

El-Nabulsi

2010

Astrophys Space Sci

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We investigate five-dimensional Brans-Dicke cosmology with spacetime described by the homogeneous, anisotropic and flat spacetime with the topology M 1 × R 3 × S 1 where S 1 is taken in the form of a circle. We conjecture throughout this letter that the extra-dimension compactifies as the visible dimensions expand like b(t) ≈ a −1 (t) and that the non-minimal coupling between the scalar field and the matter is of the form f (φ) ∝ φ 2 . The model gives rise to a transition from a decelerated epoch to an accelerated epoch for large values of the Brans-Dicke parameter ω. The model predicts crossing of the phantom divided barrier unless the universe is governed by a growing matter field.Keywords Brans-Dicke cosmology · Chameleon · Dark energy · Vacuum energy · Accelerated expansion · Phantom energy · Growing matter During the present decade, there have been considerable efforts in constructing realistic accelerating cosmological models dominated by dark energy (DE), either motivated by particle physics or by phenomenological reflections. The strong evidence confirming the low-redshift onset of the accelerated expansion of the cosmos comes directly from the CMBR dataset of the Three-Year WMAP observations and is indirectly supported by various other cosmological observations using combined WMAP data and data from the Supernova Legacy Survey of type SNeIa and large galaxy

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Living with phantoms fields in a sheet spacetime

Cited by 34 publications

References 117 publications

Noncommutative accelerated multidimensional universe dominated by quintessence

Noncommutative accelerated multidimensional universe dominated by quintessence

The Galerkin Method for Global Solutions to the Maxwell-Boltzmann System

Five-dimensional Brans–Dicke M 1×R 3×S 1 cosmology with chameleon scalar field

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