On multifluid perturbations in scalar–tensor cosmology

Ntahompagaze, Joseph; Sahlu, Shambel; Abebe, Amare; Mbonye, Manasse R.

doi:10.1142/s0218271820501205

Cited by 12 publications

(8 citation statements)

References 33 publications

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“…The other aspect of this work focuses on linear cosmological perturbations in the 1 + 3 covariant formalism in multi-fluid systems [11,13,14] adapted to include CG fluid models. After we derive the density perturbation equations and present the solutions in a step-by step manner, both analytically and numerically, we will discuss the cosmological implications as far as large-scale structure formation is concerned on both sub-and super-horizon scales, and see if there is a breaking of background degeneracy at the level of the perturbations [11,15].…”

Section: Introductionmentioning

confidence: 99%

Confronting the Chaplygin gas with data: background and perturbed cosmic dynamics

Hough¹,

Sahlu²,

Sami³

et al. 2021

Preprint

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In this paper, we undertake a unified study of background dynamics and cosmological perturbations in the presence of the Chaplygin gas. This is done by first constraining the background cosmological parameters of different Chaplygin gas models with SNIa data, and then feeding these observationally constrained parameters in the analysis of cosmological perturbations. Based on the statistical criteria we followed, none of the models has a substantial observational support but we show that the so-called 'original' and 'generalized' Chaplygin gas models have some observational support and less observational support, respectively, whereas the 'modified' and 'modified generalized' Chaplygin gas models miss out on the less observational support category but cannot be ruled out. The so-called 'generalized cosmic Chaplygin gas' model, on the other hand, falls under the no observational support category of the statistical criterion and can be ruled out. We follow the 1 + 3 covariant formalism of perturbation theory and derive the evolution equations of the fluctuations in the matter density contrast of the matter-Chaplygin gas system for the models with some or less statistical support. The solutions to these coupled systems of equations are then computed in both short-wavelength and long-wavelength modes.

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Section: Introductionmentioning

confidence: 99%

Confronting the Chaplygin gas with data: background and perturbed cosmic dynamics

Hough¹,

Sahlu²,

Sami³

et al. 2021

Preprint

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“…This is necessary since the Universe is composed of different fluids such as relativistic particles, radiation, dust, cold dark matter and many others. The extension to a multifluid cosmology is found interesting also in different works in modified theories of gravity such as in f (R) [13,18,26], and in scalar tensor theories of gravity [27].…”

Section: Introductionmentioning

confidence: 94%

“…The harmonic decomposition technique is used in such a way that the evolution equations can be converted into ordinary differential equations for each mode [19,22,25,26,27]. On an almost FRW space-time, we consider the differential equation of the form…”

Section: Harmonic Analysismentioning

confidence: 99%

“…The general results will then be considered for polynomial f (G) model and we will use quasi-static approximation for the matter perturbations for both radiation and dust dominated epochs. In that approximation, widely used in the literature [20,26,52], all the time derivative terms for the Gauss-Bonnet term and its momentum are discarded, and only those including energy density perturbations ∆ m are kept [27].…”

Section: 4 Short Wavelength Solutionsmentioning

confidence: 99%

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Multifluid cosmology in f(G) gravity

Munyeshyaka

Ayirwanda

Twagirayezu

et al. 2022

Int. J. Geom. Methods Mod. Phys.

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The treatment of 1 + 3 covariant perturbation in a multifluid cosmology with the consideration of f (G) gravity, G being the Gauss-Bonnet term, is done in the present paper. We define a set of covariant and gauge-invariant variables to describe density, velocity and entropy perturbations for both the total matter and component fluids. We then use different techniques such as scalar decomposition, harmonic decomposition, quasi-static aproximation together with the redshift transformation to get simplified perturbation equations for analysis. We then discuss number of interesting applications like the case where the universe is filled with a mixture of radiation and Gauss-Bonnet fluids as well as dust with Gauss-Bonnet fluids for both shortand long-wavelength limits. Considering polynomial f (G) model, we get numerical solutions of energy density perturbations and show that they decay with increase in redshift. This feature shows that under f (G) gravity, specifically under the considered f (G) model, one expects that the formation of the structure in the late Universe is enhanced.

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“…In the language of the scalar-tensor theory, we write linear quantities of curvature energy density and pressure as [17]…”

Section: The Theoretical Frameworkmentioning

confidence: 99%

Large-scale structure power spectrum from scalar-tensor gravity

Ntahompagaze,

Abebe,

Mbonye

2022

Preprint

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This work deals with the computation of the power spectrum of large-scale structure using the dynamical system approach for a multi-fluid universe in scalar-tensor theory of gravity. We use the 1 + 3 covariant approach to obtain evolution equations and study the behavior of the matter power spectrum of perturbation equations. The study is based on the equivalence between f (R) theory of gravity and scalar-tensor theory of gravity. We find that, for power-law (R n ) models, with 1 < n < 1.3, we have the power spectrum evolving above general relativistic scale-invariant line. For n ≥ 1.3, the power spectrum starts with constant amplitude then it experiences oscillations and eventually saturates at finite amplitude. Such behavior is consistent with other observations in the literature. The result supports the ongoing investigations of the equivalence between f (R) and scalar-tensor theory at linear order.

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On multifluid perturbations in scalar–tensor cosmology

Cited by 12 publications

References 33 publications

Confronting the Chaplygin gas with data: background and perturbed cosmic dynamics

Confronting the Chaplygin gas with data: background and perturbed cosmic dynamics

Multifluid cosmology in f(G) gravity

Large-scale structure power spectrum from scalar-tensor gravity

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