Review on Dark Energy Models

Tawfik, A.; Dahab, Eiman Abou El

doi:10.1134/s0202289319020154

“…Hence, in order to obtain a physically and mathematically consistent picture of the Universe, two different approaches have been proposed, called the dark components model, and the dark gravity model, respectively. The dark components model [80][81][82][83][84] assumes that the Universe is filled with two (still mysterious) components, dark energy, and dark matter, respectively, components for which many proposals have been advanced. In the dark gravity approach it is assumed that the nature of the gravitational force changes on astrophysical (galactic) and cosmological scales, and that the standard Einstein equations, so successful at the level of the Solar System, must be replaced by a novel theory of gravity, like, for example, theories with geometry-matter coupling [38,41], or gravitational models built upon more general geometries than the Riemannian one.…”

Section: Introductionmentioning

confidence: 99%

Cosmological evolution and dark energy in osculating Barthel–Randers geometry

Hama

¹

,

Harkó

²

,

Sabau

³

2021

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We consider the cosmological evolution in an osculating point Barthel–Randers type geometry, in which to each point of the space-time manifold an arbitrary point vector field is associated. This Finsler type geometry is assumed to describe the physical properties of the gravitational field, as well as the cosmological dynamics. For the Barthel–Randers geometry the connection is given by the Levi-Civita connection of the associated Riemann metric. The generalized Friedmann equations in the Barthel–Randers geometry are obtained by considering that the background Riemannian metric in the Randers line element is of Friedmann–Lemaitre–Robertson–Walker type. The matter energy balance equation is derived, and it is interpreted from the point of view of the thermodynamics of irreversible processes in the presence of particle creation. The cosmological properties of the model are investigated in detail, and it is shown that the model admits a de Sitter type solution, and that an effective cosmological constant can also be generated. Several exact cosmological solutions are also obtained. A comparison of three specific models with the observational data and with the standard $$\Lambda $$ Λ CDM model is also performed by fitting the observed values of the Hubble parameter, with the models giving a satisfactory description of the observations.

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“…Furthermore, the existence of so many distinct field type models for dark energy, each one facing its own theoretical problems, leads to the problem of the existence of a single, theoretically consistent field theoretical picture of the major components of the Universe. For reviews of the dark energy models see [46][47][48][49].…”

Section: Introductionmentioning

confidence: 99%

Generalizing the coupling between geometry and matter: $$f\left( R,L_m,T\right) $$ gravity

Haghani

¹

,

Harkó

²

2021

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We generalize and unify the $$f\left( R,T\right) $$ f R , T and $$f\left( R,L_m\right) $$ f R , L m type gravity models by assuming that the gravitational Lagrangian is given by an arbitrary function of the Ricci scalar R, of the trace of the energy–momentum tensor T, and of the matter Lagrangian $$L_m$$ L m , so that $$ L_{grav}=f\left( R,L_m,T\right) $$ L grav = f R , L m , T . We obtain the gravitational field equations in the metric formalism, the equations of motion for test particles, and the energy and momentum balance equations, which follow from the covariant divergence of the energy–momentum tensor. Generally, the motion is non-geodesic, and takes place in the presence of an extra force orthogonal to the four-velocity. The Newtonian limit of the equations of motion is also investigated, and the expression of the extra acceleration is obtained for small velocities and weak gravitational fields. The generalized Poisson equation is also obtained in the Newtonian limit, and the Dolgov–Kawasaki instability is also investigated. The cosmological implications of the theory are investigated for a homogeneous, isotropic and flat Universe for two particular choices of the Lagrangian density $$f\left( R,L_m,T\right) $$ f R , L m , T of the gravitational field, with a multiplicative and additive algebraic structure in the matter couplings, respectively, and for two choices of the matter Lagrangian, by using both analytical and numerical methods.

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“…Nowadays, the mystery of nature of the so-called dark energy is one of the greatest challenges of science. It consists in to fin out the reason why the universe is expanding with some acceleration, which means, understanding the current accelerated expansion of the Universe [1]. There are many hypotheses, from modification of the Einstein equations to the proposal of exotic forms of matter, but the cosmological constant continues to be one of the most accepted candidates [2].…”

Section: Introductionmentioning

confidence: 99%

The graviton Compton mass as dark energy

Matos¹,

-Parrilla²

2021

Rev. Mex. Fís.

3

0

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One of the greatest challenges of science is to understand the current accelerated expansion of the Universe. In this work we show that by considering the quantum nature of the gravitational field, its wavelength can be associated to an effective Compton mass. We propose that this mass can be interpreted as dark energy, with a Compton wavelength given by the size of the observable Universe, implying that the dark energy varies depending on this size. If we do so, we find that: 1.- Even without any free constant for dark energy, the evolution of the Hubble parameter is exactly the same as for the LCDM model, so this model has the same predictions as LCDM. 2.- The density rate of the dark energy is ΩΛ = 0.69 which is a very similar value as the one found by the Planck satellite ΩΛ = 0.684. 3.- The dark energy has this value because it corresponds to the actual size of the radius of the Universe, thus the coincidence problem has a very natural explanation. 4.- It is possible to find also a natural explanation to why observations inferred from the local distance ladder find the value H0 = 73 km/s/Mpc for the Hubble constant, we show that if we take the variability of the dark energy into account they should measure H0 = 67.3 km/s/Mpc as well. 5.- In this model the inflationary period contains a natural successful graceful exit.

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Review on Dark Energy Models

Cited by 50 publications

References 102 publications

Cosmological evolution and dark energy in osculating Barthel–Randers geometry

Cosmological evolution and dark energy in osculating Barthel–Randers geometry

Generalizing the coupling between geometry and matter: $$f\left( R,L_m,T\right) $$ gravity

The graviton Compton mass as dark energy

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