Linear growth index of matter perturbations in Rastall gravity

Khyllep, Wompherdeiki; Dutta, Jibitesh

doi:10.1016/j.physletb.2019.134796

“…[89] impose the Rastall gravity contributions from the non-conservation of dust upon DE which makes it clustering. Then, it is suggested in [94,95] that this model resembles the standard CDM model at the background level (with an not strictly constrained, provided that the DE yields an equation of state parameter very close to minus unity), while in [96] that the evolution of the growth index displays a significant deviation from that in the standard CDM model. One of the main motivations behind such attempts is that observational signatures of non-conservation in the dark sector is expected in the non-linear regime on intermediate or small scales, and is not inconsistent with the currently available cosmological data (see [97] for details).…”

Section: Introductionmentioning

confidence: 99%

Rastall gravity extension of the standard $$\Lambda $$CDM model: theoretical features and observational constraints

Akarsu

¹

,

Katırcı

²

,

Kumar

³

et al. 2020

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We present a detailed investigation of the Rastall gravity extension of the standard $$\Lambda $$ Λ CDM model. We review the model for two simultaneous modifications of different nature in the Friedmann equation due to the Rastall gravity: the new contributions of the material (actual) sources (considered as effective source) and the altered evolution of the material sources. We discuss the role/behavior of these modifications with regard to some low redshift tensions, including the so-called $$H_0$$ H 0 tension, prevailing within the standard $$\Lambda $$ Λ CDM. We constrain the model at the level of linear perturbations, and obtain the first constraints through a robust and accurate analysis using the latest full Planck cosmic microwave background (CMB) data, with and without including baryon acoustic oscillations (BAO) data. We find that the Rastall parameter $$\epsilon $$ ϵ (null for general relativity) is consistent with zero at 68% CL (with a tendency towards positive values, $$-0.0001< \epsilon < 0.0007$$ - 0.0001 < ϵ < 0.0007 (CMB+BAO) at 68% CL), which in turn implies no significant statistical evidence for deviation from general relativity, and also a precision of $$\mathcal {O}(10^{-4})$$ O ( 10 - 4 ) for the coefficient $$-1/2$$ - 1 / 2 of the term $$g_{\mu \nu }R$$ g μ ν R in the Einstein field equations of general relativity (guaranteeing the local energy-momentum conservation). We explore the consequences led by the Rastall gravity on the cosmological parameters in the light of the observational analyses. It turns out that the effective source, with a present-day density parameter $$\Omega _\mathrm{X0}=-0.0010\pm 0.0013$$ Ω X 0 = - 0.0010 ± 0.0013 (CMB+BAO, 68% CL), dynamically screens the usual vacuum energy at high redshifts, but this mechanism barely works due to the opposition by the altered evolution of cold dark matter. Consequently, two simultaneous modifications of different nature in the Friedmann equation by the Rastall gravity act against each other, and do not help to considerably relax the low redshift tensions, including the so-called $$H_0$$ H 0 tension. Our results may offer a guide for the research community that studies the Rastall gravity in various aspects of gravitation and cosmology.

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“…by defining the so-called growth factor f (N ) := d[ln δ (m) ]/dN [154][155][156][157][158]. Due to the pre-factor (1 + s) in the r.h.s.…”

Section: Growth Of Matter Density Perturbationsmentioning

confidence: 99%

Growth of Matter Perturbations in an Interacting Dark Energy Scenario Emerging from Metric-Scalar-Torsion Couplings

Sharma

¹

,

Sur

²

2021

The 1st Electronic Conference on Universe

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We study the growth of linear matter density perturbations in a modified gravity approach of scalar field couplings with metric and torsion. In the equivalent scalar-tensor formulation, the matter fields in the Einstein frame interact as usual with an effective dark energy component, whose dynamics is presumably governed by a scalar field that sources a torsion mode. As a consequence, the matter density ceases to be self-conserved, thereby making an impact not only on the background cosmological evolution but also on the perturbative spectrum of the local inhomogeneities. In order to estimate the effect on the growth of the linear matter perturbations, with the least possible alteration of the standard parametric form of the growth factor, we resort to a suitable Taylor expansion of the corresponding exponent, known as the growth index, about the value of the cosmic scale factor at the present epoch. In particular, we obtain an appropriate fitting formula for the growth index in terms of the coupling function and the matter density parameter. While the overall parametric formulation of the growth factor is found to fit well with the latest redshift-space-distortion (RSD) and the observational Hubble (OH) data at low redshifts, the fitting formula enables us to constrain the growth index to well within the concordant cosmological limits, thus ensuring the viability of the formalism.

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“…From (13), we can define the matter domination as a scenario where m ≈ 1 and φ ≈ 0. Similarly, we can also define from (13), a kinetic dominated solution or potential dominated solution when the first two terms or the last term in (11) dominate over the others, respectively.…”

Section: Non-minimal Coupled Scalar Field Modelmentioning

confidence: 99%

“…One can also predict the sensitivity of the solution to initial conditions. Dynamical system methods have been used extensively in cosmology; see [3][4][5][6][7][8][9][10][11][12][13][14][15] for relevant work and [16] for a comprehensive review.…”

Section: Introductionmentioning

confidence: 99%

Cosmological dynamics and bifurcation analysis of the general non-minimal coupled scalar field models

Khyllep

¹

,

Dutta

²

2021

Self Cite

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Non-minimal coupled scalar field models are well-known for providing interesting cosmological features. These include a late-time dark energy behavior, a phantom dark energy evolution without singularity, an early-time inflationary Universe, scaling solutions, convergence to the standard $$\Lambda $$ Λ CDM, etc. While the usual stability analysis helps us determine the evolution of a model geometrically, bifurcation theory allows us to precisely locate the parameters’ values describing the global dynamics without a fine-tuning of initial conditions. Using the center manifold theory and bifurcation analysis, we show that the general model undergoes a transcritical bifurcation, predicting us to tune our models to have certain desired dynamics. We obtained a class of models and a range of parameters capable of describing a cosmic evolution from an early radiation era towards a late time dark energy era over a wide range of initial conditions. There is also a possible scenario of crossing the phantom divide line. We also find a class of models where the late time attractor mechanism is indistinguishable from a structurally stable general relativity-based model; thus, we can elude the big rip singularity generically. Therefore, bifurcation theory allows us to select models that are viable with cosmological observations.

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Linear growth index of matter perturbations in Rastall gravity

Cited by 35 publications

References 51 publications

Rastall gravity extension of the standard $$\Lambda $$CDM model: theoretical features and observational constraints

Rastall gravity extension of the standard $$\Lambda $$CDM model: theoretical features and observational constraints

Growth of Matter Perturbations in an Interacting Dark Energy Scenario Emerging from Metric-Scalar-Torsion Couplings

Cosmological dynamics and bifurcation analysis of the general non-minimal coupled scalar field models

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