Coupled scalar fields in the late Universe: the mechanical approach and the late cosmic acceleration

Burgazli, Alvina; Zhuk, Alexander; Morais, João; Bouhmadi-López, Mariam; Kumar, K. Sravan

doi:10.1088/1475-7516/2016/09/045

Cited by 6 publications

(19 citation statements)

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“…We note that coupled states of perfect fluids were investigated in the case of a perfect fluid with a constant equation of state parameter [25] and for the following cosmological scenarios and constituents of the Universe: quark-gluon nuggets [27], the CPL model [28], Chaplygin gas [29], nonlinear f (R) gravity [30], as well as the models with a scalar field [31,32] and dark sector interactions [33,34].…”

Section: Equations For Gravitational Potential φmentioning

confidence: 99%

Scalar and vector perturbations in a universe with discrete and continuous matter sources

Eingorn

Kiefer

Zhuk

2016

J. Cosmol. Astropart. Phys.

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Abstract. We study a universe filled with dust-like matter in the form of discrete inhomogeneities (e.g., galaxies and their groups and clusters) and two sets of perfect fluids with linear and nonlinear equations of state, respectively. The background spacetime geometry is defined by the FLRW metric. In the weak gravitational field limit, we develop the first-order scalar and vector cosmological perturbation theory. Our approach works at all cosmological scales (i.e. sub-horizon and super-horizon ones) and incorporates linear and nonlinear effects with respect to energy density fluctuations. We demonstrate that the scalar perturbation (i.e. the gravitational potential) as well as the vector perturbation can be split into individual contributions from each matter source. Each of these contributions satisfies its own equation. The velocity-independent parts of the individual gravitational potentials are characterized by a finite time-dependent Yukawa interaction range being the same for each individual contribution. We also obtain the exact form of the gravitational potential and vector perturbation related to the discrete matter sources. The self-consistency of our approach is thoroughly checked. The derived equations can form the theoretical basis for numerical simulations for a wide class of cosmological models.

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Section: Equations For Gravitational Potential φmentioning

confidence: 99%

Scalar and vector perturbations in a universe with discrete and continuous matter sources

Eingorn

Kiefer

Zhuk

2016

J. Cosmol. Astropart. Phys.

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“…where in [26], we set V ∞ to zero (see lhs column of page 5 in [26]). Below, we shall consider some more general and interesting examples.…”

Section: Scalar Field Fluctuation ϕ =mentioning

confidence: 99%

“…In this sense, these fluids are coupled to the inhomogeneities [21]. Such fluids were considered in our previous papers [22][23][24][25][26]. On the other hand, we have shown [27] that fluids with a linear EoS (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…On our previous paper [26], we have considered a canonical scalar field and demonstrated that this scalar field can be coupled. At the background level, such a coupled scalar field is being considered as a one-component perfect fluid that has a constant EoS parameter w = −1/3, unsuitable, therefore, to explain the late-time acceleration for the Universe.…”

Section: Introductionmentioning

confidence: 99%

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K-essence model from the mechanical approach point of view: coupled scalar field and the late cosmic acceleration

Bouhmadi-López

Kumar

Marto

et al. 2016

J. Cosmol. Astropart. Phys.

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In this paper, we consider the Universe at the late stage of its evolution and deep inside the cell of uniformity. At these scales, we can consider the Universe to be filled with dust-like matter in the form of discretely distributed galaxies, a K-essence scalar field, playing the role of dark energy, and radiation as matter sources. We investigate such a Universe in the mechanical approach. This means that the peculiar velocities of the inhomogeneities (in the form of galaxies) as well as the fluctuations of the other perfect fluids are nonrelativistic. Such fluids are designated as coupled because they are concentrated around the inhomogeneities. In the present paper, we investigate the conditions under which the K-essence scalar field with the most general form for its action can become coupled. We investigate at the background level three particular examples of the K-essence models: (i) the pure kinetic K-essence field, (ii) a K-essence with a constant speed of sound and (iii) the K-essence model with the Lagrangian bX+cX 2 −V (φ). We demonstrate that if the K-essence is coupled, all these K-essence models take the form of multicomponent perfect fluids where one of the component is the cosmological constant. Therefore, they can provide the late-time cosmic acceleration and be simultaneously compatible with the mechanical approach.

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“…By approximating the inhomogeneities of our universe as delta function sources, a first order analytical formalism for the cosmological scalar and vector perturbations for the ΛCDM model was developed recently in [46], where a Yukawa-like fall-off of the gravitational potential was derived at large scales. Various extensions of this work, including the case of interacting fluid sources, can be found in [47,48,49,50,51,52]. Discussions on the N -body simulations in the context of cosmic screening can be seen in [53,54].…”

Section: Introductionmentioning

confidence: 99%

Cosmological screening and the phantom braneworld model

et al. 2018

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The scalar and vector cosmological perturbations at all length scales of our Universe are studied in the framework of the phantom braneworld model. The model is characterized by the parameter ΩM ≡ M 3 /2m 2 H0, with M and m the 5-and 4-dimensional Planck scales, respectively, and H0 the Hubble parameter today, while ΩM → 0 recovers the ΛCDM model. Ignoring the backreaction due to the peculiar velocities and also the bulk cosmological constant, allows the explicit computation of the gravitational potentials, Φ and Ψ. They exhibit exponentially decreasing screening behaviour characterized by a screening length which is a function of the quasidensity parameter ΩM .the study of gravitational lensing in this model. While the extra dimension is usually taken to be spacelike, we refer our reader to [13] for a timelike extra dimension.Discussions on static solutions such as a black hole in the BW model can be seen in [14,15,16,17] and references therein. For the so called two branch RS-I model, from the modification of Newton's law, the upper bound on the bulk anti-de Sitter radius turns out to be l 14 µm; whereas for the one branch RS-II model, the binary gravity wave data puts a bound : l 3.9 µm [18]. Probing the extra dimensional effects by studying the strong gravitational lensing can be seen in [19]. We refer our reader to [20] for a modification of the RS model with cosmological constants associated with both the bulk and the brane, fine tuned to make the bulk flat. This scenario is in particular helpful to estimate the energy lost by the brane via the Kaluza-Klein gravitons. In [21,22], the effect of brane -bulk energy exchange on cosmology was investigated and a model where our current universe is obtained as a late time attractor was proposed. We further refer our reader to [23] for a vast review and an exhaustive list of references pertaining to gravity and cosmology in the context of the braneworld model.In this paper, we shall be interested in an extension of the Dvali-Gabadadze-Porrati braneworld (DGP) model [24]-[27] containing in the action, the 4-dimensional Ricci scalar on the brane, induced by the one loop correction due to the graviton-matter interaction, and the extrinsic curvature of the brane. This model, unlike the Randall-Sundrum case, modifies gravity only beyond a characteristic length scale, depending on the five-and four-dimensional Newton constants. The relevant equation of motion gives rise to two branches of cosmological solutions, both with flat spatial sections, one being self accelerated without requiring any dark energy/cosmological constant, whereas the other branch (the normal branch) requires at least one cosmological constant to accommodate for the current accelerated expansion [28,29,30]. However, the former was shown to have ghost instability in subsequent works [31,32], leaving only the "normal" branch to be a possible alternative to the ΛCDM model. Furthermore, the equation of state parameter for the effective dark energy source is time dependent, w(t), and turns out to be less...

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Coupled scalar fields in the late Universe: the mechanical approach and the late cosmic acceleration

Cited by 6 publications

References 50 publications

Scalar and vector perturbations in a universe with discrete and continuous matter sources

Scalar and vector perturbations in a universe with discrete and continuous matter sources

K-essence model from the mechanical approach point of view: coupled scalar field and the late cosmic acceleration

Cosmological screening and the phantom braneworld model

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