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Deceleration parameter

About: Deceleration parameter is a research topic. Over the lifetime, 1776 publications have been published within this topic receiving 89440 citations.


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TL;DR: In this article, the authors consider a cosmology in which a spherically symmetric large scale inhomogeneous enhancement or a void are described by an inhomogenous metric and Einstein's gravitational equations.
Abstract: We consider a cosmology in which a spherically symmetric large scale inhomogeneous enhancement or a void are described by an inhomogeneous metric and Einstein's gravitational equations. For a flat matter dominated universe the inhomogeneous equations lead to luminosity distance and Hubble constant formulae that depend on the location of the observer. For a general inhomogeneous solution, it is possible for the deceleration parameter to differ significantly from the FLRW result. The deceleration parameter q0 can be interpreted as q0 > 0 in a FLRW universe (q0 = 1/2 for a flat matter dominated universe) and q0 < 0 as inferred from the inhomogeneous enhancement that is embedded in a FLRW universe. A spatial volume averaging of local regions in the backward light cone has to be performed for the inhomogeneous solution at late times to decide whether the decelerating parameter q can be negative for a positive energy condition. The CMB temperature fluctuations across the sky can be unevenly distributed in the northern and southern hemispheres in the inhomogeneous matter dominated solution, in agreement with the analysis of the WMAP power spectrum data by several authors. The model can possibly explain the anomalous alignment of the quadrupole and octopole moments observed in the WMAP data.

102 citations

Journal ArticleDOI
TL;DR: In this paper, the authors considered the Einstein field equations with perfect fluid source and variable Λ andG for the Robertson-Walker metric and found perfect gas equation of state models in the Euclidean and non-Euclidean cases.
Abstract: We consider the Einstein field equations with perfect fluid source and variable Λ andG for the Robertson-Walker metric. When conservation of energy momentum is postulated and the deceleration parameter is assumed constant, we find perfect gas equation of state models in the Euclidean and non-Euclidean cases. The resulting models offer an alternative to the inflationary scenario; they also explain the huge value of the cosmological term in the early universe.

101 citations

Journal ArticleDOI
TL;DR: In this article, the dynamics of a minimally coupled scalar field in the expanding universe is discussed with special reference to phantom cosmology and the evolution of the universe with a phantom field vis-a-vis a quintessence field is compared.
Abstract: The dynamics of a minimally coupled scalar field in the expanding universe is discussed with special reference to phantom cosmology The evolution of the universe with a phantom field vis-a-vis a quintessence field is compared Phantom cosmologies are found to have two special features i) occurrence of a singularity where the scale factor, the energy density and Ricci curvature scalar diverge to infinity This singularity occurs at a finite time, depending on w during cosmic evolution, ii) degeneracy in the determination of w(z_m) for a particular transition redshift z_m which seems to impart similar observational properties to corresponding phantom and quintessence models and makes them compatible with the cosmological observations Constraints over phantom fields are derived using recent WMAP data and the range of $w$ is narrowed down to -118 < w < -093 with the corresponding value of the deceleration parameter lying in the range - 08 < q_0 < -052 An observational test, based upon the observations of low redshift galactic clusters, is suggested to discriminate between the quintessence and phantom dark energy

100 citations

Journal ArticleDOI
TL;DR: In this article, the authors considered the cosmological constant Λ as a function of the trace of the stress energy-momentum-tensor, and dub such a model "Λ(T) gravity" where they have specified a certain form of Λ (T).
Abstract: A new class of cosmological models in f(R,T) modified theories of gravity proposed by Harko et al. (Phys. Rev. D 84:024020, 2011), where the gravitational Lagrangian is given by an arbitrary function of Ricci scalar R and the trace of the stress-energy tensor T, have been investigated for a specific choice of f(R,T)=f 1(R)+f 2(T) by considering time dependent deceleration parameter. The concept of time dependent deceleration parameter (DP) with some proper assumptions yield the average scale factor $a(t) = \sinh^{\frac{1}{n}}(\alpha t)$ , where n and α are positive constants. For 0 1, the models of universe exhibit phase transition from early decelerating phase to present accelerating phase which is in good agreement with the results from recent astrophysical observations. Our intention is to reconstruct f(R,T) models inspired by this special law for the deceleration parameter in connection with the theories of modified gravity. In the present study we consider the cosmological constant Λ as a function of the trace of the stress energy-momentum-tensor, and dub such a model “Λ(T) gravity” where we have specified a certain form of Λ(T). Such models may display better uniformity with the cosmological observations. The statefinder diagnostic pair {r,s} parameter has been embraced to characterize different phases of the universe. We also discuss the physical consequences of the derived models.

100 citations

Journal ArticleDOI
TL;DR: In this paper, the authors propose higher-order energy conditions which relate time derivatives of the energy density and pressure which may be useful in general relativity, and also propose higher order energy conditions for Friedmann cosmology.

99 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023120
2022210
2021128
2020116
2019107
201892