Observational constraints on the acceleration of the Universe

In order to test if there is energy transfer between dark energy (DE) and dark matter (DM), we investigate cosmological constraints on two forms of nontrivial interaction between the DM sector and the sector responsible for the acceleration of the universe, in light of the newly revised observations including OHD, CMB, BAO and SNe Ia. More precisely, we find the same tendencies for both phenomenological forms of the interaction term Q = 3γHρ, i.e. the parameter γ to be a small number, |γ| ≈ 10-2. However, concerning the sign of the interaction parameter, we observe that γ > 0 when the interaction between dark sectors is proportional to the energy density of dust matter, whereas the negative coupling (γ < 0) is preferred by observations when the interaction term is proportional to DE density. We further discuss two possible explanations to this incompatibility and apply a quantitative criteria to judge the severity of the coincidence problem. Results suggest that the γm IDE model with a positive coupling may alleviate the coincidence problem, since its coincidence index C is smaller than that for the γd IDE model, the interacting quintessence and phantom models by four orders of magnitude.

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Inflation and dark energy in f(R, X, ϕ) gravity

Modern Physics Letters A ◽

10.1142/s0217732318502152 ◽

2018 ◽

Vol 33 (36) ◽

pp. 1850215 ◽

Cited By ~ 2

Author(s):

A. I. Keskin

Keyword(s):

Dark Energy ◽

Scalar Field ◽

Observational Data ◽

Observational Constraints ◽

Late Time ◽

Late Time Acceleration ◽

Acceleration Of The Universe ◽

The Universe

In this study, we show the early inflation and the late-time acceleration of the universe in the model [Formula: see text], which shows a minimum connection between geometry and scalar field. Both a quintessential inflation and the super inflation mechanism are discussed in the model, and for both the cases the some conditions for n are obtained under the constraint of the observational data. However, the oscillations of the scalar field are analyzed in view of observational constraints. By means of the oscillations of the scalar field, besides the inflation of the universe a condition of n for the late-time quintessence type of dark energy is obtained.

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Chameleon field and the late time acceleration of the Universe

Pramana ◽

10.1007/s12043-010-0044-5 ◽

2010 ◽

Vol 74 (3) ◽

pp. 481-489 ◽

Cited By ~ 19

Author(s):

Narayan Banerjee ◽

Sudipta Das ◽

Koyel Ganguly

Keyword(s):

Late Time ◽

Late Time Acceleration ◽

Acceleration Of The Universe ◽

The Universe

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Cosmological constant and late transient acceleration of the universe in the Horava–Witten heterotic M-theory on S1/Z2

Physics Letters B ◽

10.1016/j.physletb.2008.04.003 ◽

2008 ◽

Vol 663 (3) ◽

pp. 147-151 ◽

Cited By ~ 19

Author(s):

Yungui Gong ◽

Anzhong Wang ◽

Qiang Wu

Keyword(s):

Cosmological Constant ◽

Acceleration Of The Universe ◽

M Theory ◽

The Universe

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Hamiltonian formalism for nonlocal gravity models

International Journal of Geometric Methods in Modern Physics ◽

10.1142/s0219887822500360 ◽

2022 ◽

Author(s):

Pawan Joshi ◽

Utkarsh Kumar ◽

Sukanta Panda

Keyword(s):

Ricci Tensor ◽

Degrees Of Freedom ◽

Hamiltonian Formalism ◽

Riemann Tensor ◽

Ricci Scalar ◽

Gravity Models ◽

Lagrangian Formalism ◽

Acceleration Of The Universe ◽

Nonlocal Action ◽

The Universe

Nonlocal gravity models are constructed to explain the current acceleration of the universe. These models are inspired by the infrared correction appearing in Einstein–Hilbert action. Here, we develop the Hamiltonian formalism of a nonlocal model by considering only terms to quadratic order in Riemann tensor, Ricci tensor and Ricci scalar. We show how to count degrees of freedom using Hamiltonian formalism including Ricci tensor and Ricci scalar terms. In this model, we have also worked out with a choice of a nonlocal action which has only two degrees of freedom equivalent to GR. Finally, we find the existence of additional constraints in Hamiltonian required to remove the ghosts in our full action. We also compare our results with that of obtained using Lagrangian formalism.

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Natural inflation after Planck 2018

Journal of Cosmology and Astroparticle Physics ◽

10.1088/1475-7516/2022/01/022 ◽

2022 ◽

Vol 2022 (01) ◽

pp. 022

Author(s):

Nina K. Stein ◽

William H. Kinney

Keyword(s):

Symmetry Breaking ◽

High Precision ◽

Confidence Region ◽

Hubble Constant ◽

Current Data ◽

Electroweak Symmetry Breaking ◽

Observational Constraints ◽

Electroweak Symmetry ◽

History Of ◽

The Universe

Abstract We calculate high-precision constraints on Natural Inflation relative to current observational constraints from Planck 2018 + BICEP/Keck(BK15) Polarization + BAO on r and n S, including post-inflationary history of the universe. We find that, for conventional post-inflationary dynamics, Natural Inflation with a cosine potential is disfavored at greater than 95% confidence out by current data. If we assume protracted reheating characterized by w̅>1/3, Natural Inflation can be brought into agreement with current observational constraints. However, bringing unmodified Natural Inflation into the 68% confidence region requires values of T re below the scale of electroweak symmetry breaking. The addition of a SHOES prior on the Hubble Constant H 0 only worsens the fit.

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On generalized Lemaitre–Tolman–Bondi metric: Fractal matter at the end of matter–antimatter recombination

International Journal of Modern Physics D ◽

10.1142/s0218271821500863 ◽

2021 ◽

pp. 2150086

Author(s):

Sergio L. Cacciatori ◽

Alessio Marrani ◽

Federico Re

Keyword(s):

Dark Matter ◽

Relativistic Effects ◽

Partial Explanation ◽

First Order ◽

Acceleration Of The Universe ◽

Particular Solution ◽

Ancient Times ◽

The Universe ◽

Recombination Epoch ◽

Ltb Metric

Many recent researches have investigated the deviations from the Friedmannian cosmological model, as well as their consequences on unexplained cosmological phenomena, such as dark matter and the acceleration of the Universe. On one hand, a first-order perturbative study of matter inhomogeneity returned a partial explanation of dark matter and dark energy, as relativistic effects due to the retarded potentials of far objects. On the other hand, the fractal cosmology, now approximated by a Lemaitre–Tolman–Bondi (LTB) metric, results in distortions of the luminosity distances of SNe Ia, explaining the acceleration as apparent. In this work, we extend the LTB metric to ancient times. The origin of the fractal distribution of matter is explained as the matter remnant after the matter–antimatter recombination epoch. We show that the evolution of such a inhomogeneity necessarily requires a dynamical generalization of LTB, and we propose a particular solution.

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Observational constraints of a new unified dark fluid and the H0 tension

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2753 ◽

2019 ◽

Vol 490 (2) ◽

pp. 2071-2085 ◽

Cited By ~ 10

Author(s):

Weiqiang Yang ◽

Supriya Pan ◽

Andronikos Paliathanasis ◽

Subir Ghosh ◽

Yabo Wu

Keyword(s):

Dark Matter ◽

Dark Energy ◽

Large Scale ◽

Cold Dark Matter ◽

Early Time ◽

Observational Constraints ◽

Minimal Extension ◽

Energy Evolution ◽

The Universe ◽

Different Sources

ABSTRACT Unified cosmological models have received a lot of attention in astrophysics community for explaining both the dark matter and dark energy evolution. The Chaplygin cosmologies, a well-known name in this group have been investigated matched with observations from different sources. Obviously, Chaplygin cosmologies have to obey restrictions in order to be consistent with the observational data. As a consequence, alternative unified models, differing from Chaplygin model, are of special interest. In the present work, we consider a specific example of such a unified cosmological model, that is quantified by only a single parameter μ, that can be considered as a minimal extension of the Λ-cold dark matter cosmology. We investigate its observational boundaries together with an analysis of the universe at large scale. Our study shows that at early time the model behaves like a dust, and as time evolves, it mimics a dark energy fluid depicting a clear transition from the early decelerating phase to the late cosmic accelerating phase. Finally, the model approaches the cosmological constant boundary in an asymptotic manner. We remark that for the present unified model, the estimations of H0 are slightly higher than its local estimation and thus alleviating the H0 tension.

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Cosmological dynamics of f(R) models in dynamical system analysis

International Journal of Modern Physics A ◽

10.1142/s0217751x20501249 ◽

2020 ◽

Vol 35 (22) ◽

pp. 2050124

Author(s):

Parth Shah ◽

Gauranga C. Samanta

Keyword(s):

Dynamical System ◽

Asymptotic Behavior ◽

Critical Points ◽

System Analysis ◽

Late Time ◽

Field Equations ◽

Acceleration Phase ◽

First Case ◽

Acceleration Of The Universe ◽

The Universe

In this work we try to understand the late-time acceleration of the universe by assuming some modification in the geometry of the space and using dynamical system analysis. This technique allows to understand the behavior of the universe without analytically solving the field equations. We study the acceleration phase of the universe and stability properties of the critical points which could be compared with observational results. We consider an asymptotic behavior of two particular models [Formula: see text] and [Formula: see text] with [Formula: see text], [Formula: see text], [Formula: see text] for the study. As a first case we fix the value of [Formula: see text] and analyze for all [Formula: see text]. Later as second case, we fix the value of [Formula: see text] and calculation are done for all [Formula: see text]. At the end all the calculations for the generalized case have been shown and results have been discussed in detail.

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Cosmic acceleration with tachyon field

Modern Physics Letters A ◽

10.1142/s0217732318501997 ◽

2018 ◽

Vol 33 (34) ◽

pp. 1850199 ◽

Cited By ~ 1

Author(s):

A. I. Keskin

Keyword(s):

Scalar Field ◽

Energy Momentum Tensor ◽

Momentum Tensor ◽

Cosmic Acceleration ◽

Late Time ◽

De Sitter ◽

Tachyon Field ◽

Minimal Coupling ◽

Acceleration Of The Universe ◽

The Universe

In this study, we examine two models of the scalar field, that is, a normal scalar field and a tachyon scalar field in [Formula: see text] gravity to describe cosmic acceleration of the universe, where [Formula: see text], [Formula: see text] and [Formula: see text] are Ricci curvature scalar, trace of energy–momentum tensor and kinetic energy of scalar field [Formula: see text], respectively. Using the minimal-coupling Lagrangian [Formula: see text], for both the scalar models we obtain a viable cosmological system, where [Formula: see text] and [Formula: see text] are real constants. While a normal scalar field gives a system describing expansion from the deceleration to the late-time acceleration, tachyon field together with [Formula: see text] in the system produces a quintessential expansion which is very close to de Sitter point, where we find a new condition [Formula: see text] for inflation.

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