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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 detect and identify 12 molecular absorption lines in the spectrum of PKS1830-211, a radio source with a redshift of 0.89.
Abstract: GRAVITATIONAL lensing can be used to derive fundamental cosmo-logical parameters, provided that the redshift of the lens and the structure of its potential well are known1. The radio source PKS1830–211—a lensed quasar2–5 whose components are separated by about 1 arcsecond—is ideal for such an examination, but until recently the redshift of the lens has been unknown. Here we report the detection and identification of 12 molecular absorption lines in the spectrum of PKS1830–211; the lines originate in the lensing source, which is probably a spiral galaxy, at a redshift of ~0.89. Only one of the lensed components is covered by the intervening molecular gas; when combined with the strong variability in the quasar, this creates a unique opportunity to measure the difference in the light travel time for the two components, which depends in part on the Hubble constant and the cosmic deceleration parameter.
207 citations
TL;DR: In this paper, the scale dependence of G and Λ is governed by a set of renormalization group equations which is coupled to Einstein's equation in a consistent way, and it turns out that in the late Universe the vacuum energy density is automatically adjusted so as to equal precisely the matter energy density, and that the deceleration parameter approaches q =−1/4.
205 citations
TL;DR: In this paper, the authors used type Ia supernovae (SN Ia) data in combination with recent baryonic acoustic oscillations (BAO) and cosmic microwave background (CMB) observations to constrain a kink-like parametrization of the deceleration parameter (q).
Abstract: We use type Ia supernovae (SN Ia) data in combination with recent baryonic acoustic oscillations (BAO) and cosmic microwave background (CMB) observations to constrain a kink-like parametrization of the deceleration parameter (q). This q-parametrization can be written in terms of the initial (qi) and present (q0) values of the deceleration parameter, the redshift of the cosmic transition from deceleration to acceleration (zt) and the redshift width of such transition (τ). By assuming a flat space geometry, qi = 1/2 and adopting a likelihood approach to deal with the SN Ia data we obtain, at the 68% confidence level (C.L.), that: zt = 0.56+0.13−0.10, τ = 0.47+0.16−0.20 and q0 = −0.31+0.11−0.11 when we combine BAO/CMB observations with SN Ia data processed with the MLCS2k2 light-curve fitter. When in this combination we use the SALT2 fitter we get instead, at the same C.L.: zt = 0.64+0.13−0.07, τ = 0.36+0.11−0.17 and q0 = −0.53+0.17−0.13. Our results indicate, with a quite general and model independent approach, that MLCS2k2 favors Dvali-Gabadadze-Porrati-like cosmological models, while SALT2 favors ΛCDM-like ones. Progress in determining the transition redshift and/or the present value of the deceleration parameter depends crucially on solving the issue of the difference obtained when using these two light-curve fitters.
201 citations
TL;DR: In this article, the authors considered the interacting holographic model of dark energy to investigate the validity of the generalized second laws of thermodynamics in a non-flat (closed) universe enclosed by the event horizon measured from the sphere of the horizon named $L$.
Abstract: In the present paper we consider the interacting holographic model of dark energy to investigate the validity of the generalized second laws of thermodynamics in non-flat (closed) universe enclosed by the event horizon measured from the sphere of the horizon named $L$. We show that for $L$ as the system's IR cut-off the generalized second law is respected for the special range of the deceleration parameter.
191 citations
TL;DR: In this paper, the authors examined locally rotationally symmetric Bianchi type I cosmological models in the presence of dynamically anisotropic dark energy and perfect fluid, where the conservation of the energy-momentum tensor of the DE is assumed to consist of two separately additive conserved parts.
Abstract: Locally rotationally symmetric Bianchi type I cosmological models are examined in the presence of dynamically anisotropic dark energy and perfect fluid. We assume that the dark energy (DE) is minimally interacting, has dynamical energy density, anisotropic equation of state parameter (EoS). The conservation of the energy-momentum tensor of the DE is assumed to consist of two separately additive conserved parts. A special law is assumed for the deviation from isotropic EoS, which is consistent with the assumption on the conservation of the energy-momentum tensor of the DE. Exact solutions of Einstein’s field equations are obtained by assuming a special law of variation for the mean Hubble parameter, which yields a constant value of the deceleration parameter. Geometrical and kinematic properties of the models and the behaviour of the anisotropy of the dark energy have been carried out. The models give dynamically anisotropic expansion history for the universe that allows to fine tune the isotropization of the Bianchi metric, hence the CMB anisotropy.
190 citations