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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, the authors investigated the cosmographic problem using the bias-variance trade-off and found that cosmography up to the second order is the best approximation.
Abstract: In the present paper, we investigate the cosmographic problem using the bias–variance trade-off. We find that both the z-redshift and the $$y=z/(1+z)$$ -redshift can present a small bias estimation. It means that the cosmography can describe the supernova data more accurately. Minimizing risk, it suggests that cosmography up to the second order is the best approximation. Forecasting the constraint from future measurements, we find that future supernova and redshift drift can significantly improve the constraint, thus having the potential to solve the cosmographic problem. We also exploit the values of cosmography on the deceleration parameter and equation of state of dark energy w(z). We find that supernova cosmography cannot give stable estimations on them. However, much useful information was obtained, such as that the cosmography favors a complicated dark energy with varying w(z), and the derivative $${\text {d}}w/{\text {d}}z <0$$ for low redshift. The cosmography is helpful to model the dark energy.

31 citations

Journal ArticleDOI
TL;DR: Karami et al. as discussed by the authors considered a non-flat FRW universe and studied the behaviors of the equation-of-state (EoS) parameter ω and of the deceleration parameter q.
Abstract: The present work is motivated by the study of the paper K. Karami, A. Abdolmaleki, J. Cosmol. Astropart. Phys. 04, 007 (2012), where the generalized second law (GSL) of thermodynamics has been investigated for a flat FRW universe for three viable models of f(T) gravity. We have here considered a non-flat universe and, accordingly, studied the behaviors of the equation-of-state (EoS) parameter ω and of the deceleration parameter q. Subsequently, using the first law of thermodynamics, we derived the expressions for the time derivative of the total entropy of a universe enveloped by apparent horizon. In the next phase, with the choice of scale factor a(t) pertaining to an emergent universe, we have investigated the sign of the time derivatives of total entropy for the models of f(T) gravity considered.

31 citations

Journal ArticleDOI
TL;DR: In this paper, a massless scalar field with a possible coupling to the Ricci scalar in a D-dimensional Friedmann-Lemaitre-Robertson-Walker space-time with a constant deceleration parameter was considered.
Abstract: In this paper we consider a massless scalar field, with a possible coupling {xi} to the Ricci scalar in a D dimensional Friedmann-Lemaitre-Robertson-Walker space-time with a constant deceleration parameter q={epsilon}-1, {epsilon}=-H/H{sup 2}. Correlation functions for the Bunch-Davies vacuum of such a theory have long been known to be infrared divergent for a wide range of values of {epsilon}. We resolve these divergences by explicitly matching the space-time under consideration to a space-time without infrared divergencies. Such a procedure ensures that all correlation functions with respect to the vacuum in the space-time of interest are infrared finite. In this newly defined vacuum we construct the coincidence limit of the propagator and as an example calculate the expectation value of the stress-energy tensor. We find that this approach gives both in the ultraviolet and in the infrared satisfactory results. Moreover, we find that, unless the effective mass due to the coupling to the Ricci scalar {xi}R is negative, quantum contributions to the energy density always dilute away faster, or just as fast, as the background energy density. Therefore, quantum backreaction is insignificant at the one-loop order, unless {xi}R is negative. Finally we compare this approach with known results where the infrared ismore » regulated by placing the Universe in a finite box. In an accelerating universe, the results are qualitatively the same, provided one identifies the size of the Universe with the physical Hubble radius at the time of the matching. In a decelerating universe, however, the two schemes give different late time behavior for the quantum stress-energy tensor. This happens because in this case the length scale at which one regulates the infrared becomes sub-Hubble at late times.« less

31 citations

Journal ArticleDOI
TL;DR: In this paper, the authors considered a modified theory of gravity in which, in general, the gravitational Lagrangian is given by an arbitrary function of the Ricci scalar and the trace of the energy-momentum tensor.
Abstract: We consider $$f\left( {R,T} \right) $$ modified theory of gravity in which, in general, the gravitational Lagrangian is given by an arbitrary function of the Ricci scalar and the trace of the energy–momentum tensor. We indicate that in this type of the theory, the coupling energy–momentum tensor is not conserved. However, we mainly focus on a particular model that matter is minimally coupled to the geometry in the metric formalism and wherein, its coupling energy–momentum tensor is also conserved. We obtain the corresponding Raychaudhuri dynamical equation that presents the evolution of the kinematic quantities. Then for the chosen model, we derive the behavior of the deceleration parameter, and show that the coupling term can lead to an acceleration phase after the matter dominated phase. On the other hand, the curvature of the universe corresponds with the deviation from parallelism in the geodesic motion. Thus, we also scrutinize the motion of the free test particles on their geodesics, and derive the geodesic deviation equation in this modified theory to study the accelerating universe within the spatially flat FLRW background. Actually, this equation gives the relative accelerations of adjacent particles as a measurable physical quantity, and provides an elegant tool to investigate the timelike and the null structures of spacetime geometries. Then, through the null deviation vector, we find the observer area–distance as a function of the redshift for the chosen model, and compare the results with the corresponding results obtained in the literature.

31 citations

Journal ArticleDOI
TL;DR: In this paper, three models of f(R) modified gravity including higher order terms based on different equation of state parameter were studied, and the behavior of some important cosmological parameters, like the Hubble expansion H parameter and the deceleration parameter q.
Abstract: In this paper, we study three models of f(R) modified gravity including higher order terms based on different equation of state parameter. We also assume variable G and $\Lambda$. By using numerical analysis, we obtain the behavior of some important cosmological parameters, like the Hubble expansion H parameter and the deceleration parameter q. The statefinder diagnostics is also performed for all models.

31 citations


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