Alternative dark energy models: an overview

Lima, J. A. S.

doi:10.1590/s0103-97332004000200009

Cited by 132 publications

(89 citation statements)

References 53 publications

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“…In view of vanishing of the divergence of Einstein tensor, we have (9) The usual energy conservation equation of general relativity quantities is (10) Equation (9) together with (10) puts G and  in some sort of coupled field given by (11) implying that  is a constant whenever G is constant. Using equation (2 1 ) in equation (10) and then integrating, we get k > 0…”

Section: The Metric and Field Equationsmentioning

confidence: 99%

2-A Cosmological Model with Varying G and ∧ in General Relativity

Harpreet¹,

Tiwari²,

Sahota³

2013

OJAppS

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Spatially homogeneous and anisotropic Cosmological models play a significant role in the description of the early stages of evolution of the universe. The problem of the cosmological constant is still unsettled. The authors recently considered time dependent G and  with Bianchi type-I Cosmological model .We considered in this paper homogeneous Bianchi type -I space-time with variable G and  containing matter in the form of a perfect fluid assuming the cosmological term proportional to R -2 (where R is scale factor). Initially the model has a point type singularity, gravitational constant G (t) is decreasing and cosmological constant  is infinite at this time. When time increases  decreases. Unlike in some earlier works we have neither assumed equation of state nor particular form of G. The model does not approach isotropy, if 't' is small .The model is quasi-isotropic for large value of 't'.

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Section: The Metric and Field Equationsmentioning

confidence: 99%

2-A Cosmological Model with Varying G and ∧ in General Relativity

Harpreet¹,

Tiwari²,

Sahota³

2013

OJAppS

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“…(14) it follows that matter and dark energy form together a system that has a conserved fourmomentum. Therefore, we can speak of an interaction between matter and dark energy [30]. In the Jordan frame of f (R) gravity, the energy-momentum tensor is always conserved [31] as a direct consequence of Eq.…”

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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“…The basic idea is closely related to early attempts aimed at solving (or at least alleviating) some cosmic mysteries, such as the "graceful exit" problem, which plague many inflationary scenarios (for recent reviews see [3,4]), and also the CCP or cosmological constant problem [5][6][7][8][9][10][11], probably, the deepest conundrum of all inflationary theories describing the very early Universe.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamical aspects of running vacuum models

2016

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The thermal history of a large class of running vacuum models in which the effective cosmological term is described by a truncated power series of the Hubble rate, whose dominant term is (H ) ∝ H n+2 , is discussed in detail. Specifically, by assuming that the ultrarelativistic particles produced by the vacuum decay emerge into space-time in such a way that its energy density ρ r ∝ T 4 , the temperature evolution law and the increasing entropy function are analytically calculated. For the whole class of vacuum models explored here we find that the primeval value of the comoving radiation entropy density (associated to effectively massless particles) starts from zero and evolves extremely fast until reaching a maximum near the end of the vacuum decay phase, where it saturates. The late-time conservation of the radiation entropy during the adiabatic FRW phase also guarantees that the whole class of running vacuum models predicts the same correct value of the present day entropy, S 0 ∼ 10 87 -10 88 (in natural units), independently of the initial conditions. In addition, by assuming Gibbons-Hawking temperature as an initial condition, we find that the ratio between the late-time and primordial vacuum energy densities is in agreement with naive estimates from quantum field theory, namely, ρ 0 /ρ I ∼ 10 −123 . Such results are independent on the power n and suggests that the observed Universe may evolve smoothly between two extreme, unstable, non-singular de Sitter phases.

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Alternative dark energy models: an overview

Cited by 132 publications

References 53 publications

2-A Cosmological Model with Varying G and ∧ in General Relativity

2-A Cosmological Model with Varying G and ∧ in General Relativity

Interacting dark energy inf(R)gravity

Thermodynamical aspects of running vacuum models

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