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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 paper, a Friedmann-like cosmological model with one, two and three free parameters is studied, where the torsion function is assumed to be proportional to a single φ (t) function coming just from the spin vector contribution of ordinary matter.
Abstract: A Friedmann like cosmological model in Einstein–Cartan framework is studied when the torsion function is assumed to be proportional to a single $$\phi (t)$$ function coming just from the spin vector contribution of ordinary matter. By analysing four different types of torsion function written in terms of one, two and three free parameters, we found that a model with $$\phi (t)=- \alpha H(t) \big ({\rho _{m}(t)}/{\rho _{0c}}\big )^n$$ is totally compatible with recent cosmological data, where $$\alpha $$ and n are free parameters to be constrained from observations, $$\rho _m$$ is the matter energy density and $$\rho _{0c}$$ the critical density. The recent accelerated phase of expansion of the universe is correctly reproduced by the contribution coming from torsion function, with a deceleration parameter indicating a transition redshift of about 0.65.

24 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present cosmological solutions for (1+3+n)-dimensional steady state universe in dilaton gravity with an arbitrary dilaton coupling constant w and exponential dilaton self-interaction potentials in the string frame.
Abstract: We present cosmological solutions for (1+3+n)-dimensional steady state universe in dilaton gravity with an arbitrary dilaton coupling constant w and exponential dilaton self-interaction potentials in the string frame. We focus particularly on the class in which the 3-space expands with a time varying deceleration parameter. We discuss the number of the internal dimensions and the value of the dilaton coupling constant to determine the cases that are consistent with the observed universe and the primordial nucleosynthesis. The 3-space starts with a decelerated expansion rate and evolves into accelerated expansion phase subject to the values of w and n, but ends with a Big Rip in all cases. We discuss the cosmological evolution in further detail for the cases w = 1 and w = 1 that permit exact solutions. We also comment on how the universe would be conceived by an observer in four dimensions who is unaware of the internal dimensions and thinks that the conventional general relativity is valid at cosmological scales.

24 citations

Journal ArticleDOI
Mario Novello1, H. Heintzmann1
TL;DR: In this article, a generalized solution of the Maxwell-Einstein equations is presented, which leads to some fascinating aspects of the universe, such as the fact that the universe has no singularity due to the coupling of longitudinal electromagnetism with space-time.
Abstract: We present a new generalized solution of Maxwell-Einstein equations (which are nonminimally coupled) which leads to some fascinating aspects of the Universe. The Cosmos has no singularity due to the coupling of longitudinal electromagnetism with space-time. It contains the Milne-Schucking cosmos as a limiting case. Our model contains a free parameter (the longitudinal electromagnetic field) which allows one to fix the density of highest compression of the Cosmos. Alternatively the parameter allows one to adjust our cosmos to the presently observed Hubble constant and the deceleration parameter. The model seems to be a viable candidate for our real cosmos as it allows one to extend the time scale of the Universe to arbitrarily large values, i.e., it is able to provide the necessary time scale for the origin of life. We speculate that the entropy is finite but intelligence in the Universe may be infinite.

24 citations

Journal ArticleDOI
TL;DR: In this paper, the generalized Chaplygin gas (GCG) model in spatially flat universe is investigated and the cosmological consequences led by GCG model including the evolution of EoS parameter, deceleration parameter and dimensionless Hubble parameter are calculated.
Abstract: The generalized Chaplygin gas (GCG) model in spatially flat universe is investigated. The cosmological consequences led by GCG model including the evolution of EoS parameter, deceleration parameter and dimensionless Hubble parameter are calculated. We show that the GCG model behaves as a general quintessence model. The GCG model can also represent the pressureless CDM model at the early time and cosmological constant model at the late time. The dependency of transition from decelerated expansion to accelerated expansion on the parameters of model is investigated. The statefinder parameters r and s in this model are derived and the evolutionary trajectories in s–r plane are plotted. Finally, based on current observational data, we plot the evolutionary trajectories in s–r and q–r planes for best fit values of the parameters of GCG model. It has been shown that although, there are similarities between GCG model and other forms of Chaplygin gas in statefinder plane, but the distance of this model from the ΛCDM fixed point in s–r diagram is shorter compare with standard Chaplygin gas model.

24 citations

Journal ArticleDOI
TL;DR: In this article, the generalized QCD ghost model of dark energy in the framework of Einstein gravity is investigated, and it is shown that the equation-of-state parameter of the ghost energy can cross the phantom line in some range of the parameter spaces.
Abstract: In this work, the generalized Quantum Chromodynamics (QCD) ghost model of dark energy in the framework of Einstein gravity is investigated. For this purpose, we use the squared sound speed $ v_{s}^{2}$ whose sign determines the stability of the model. At first, the non-interacting ghost dark energy in a Bianchi type-I (BI) background is discussed. Then the equation-of-state parameter, $ \omega_D=p_{D}/\rho_{D}$ , the deceleration parameter, and the evolution equation of the generalized ghost dark energy are obtained. It is shown that the equation-of-state parameter of the ghost dark energy can cross the phantom line ( $ \omega=-1$ in some range of the parameter spaces. Then, this investigation was extended to the general scheme for modified $ f(R,T)$ gravity reconstruction from a realistic case in an anisotropic Bianchi type-I cosmology, using the dark matter and ghost dark energy. Special attention is taken into account for the case in which the function f is given by $ f(R,T)=f_{1}(R) +f_{2}(T)$ . We consider a specific model which permits the standard continuity equation in this modified theory. Besides $ \Omega_{\Lambda}$ and $ \Omega$ in standard Einstein cosmology, another density parameter, $ \Omega_{\sigma}$ , is expected by the anisotropy. This theory implies that if $ \Omega_{\sigma}$ is zero then it yields the FRW universe model. Interestingly enough, we find that the corresponding f (R, T) gravity of the ghost DE model can behave like phantom or quintessence of the selected models which describe the accelerated expansion of the universe.

24 citations


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