Topic
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 apply Gaussian processes (GP) in order to impose constraints on teleparallel gravity and its $f(T)$ extensions, and reconstruct the model-independent evolution of the dark energy equation of state.
Abstract: We apply Gaussian processes (GP) in order to impose constraints on teleparallel gravity and its $f(T)$ extensions. We use available $H(z)$ observations from (i) cosmic chronometers data (CC); (ii) Supernova Type Ia (SN) data from the compressed Pantheon release together with the CANDELS and CLASH Multi-Cycle Treasury programs; and (iii) baryonic acoustic oscillation (BAO) datasets from the Sloan Digital Sky Survey. For the involved covariance functions, we consider four widely used choices, namely the square exponential, Cauchy, Matern and rational quadratic kernels, which are consistent with one another within 1$\sigma$ confidence levels. Specifically, we use the GP approach to reconstruct a model-independent determination of the Hubble constant $H_0$, for each of these kernels and dataset combinations. These analyses are complemented with three recently announced literature values of $H_0$, namely (i) Riess $H_0^{\rm R} = 74.22 \pm 1.82 \,{\rm km\, s}^{-1} {\rm Mpc}^{-1}$; (ii) H0LiCOW Collaboration $H_0^{\rm HW} = 73.3^{+1.7}_{-1.8} \,{\rm km\, s}^{-1} {\rm Mpc}^{-1}$; and (iii) Carnegie-Chicago Hubble Program $H_0^{\rm TRGB} = 69.8 \pm 1.9 \,{\rm km\, s}^{-1} {\rm Mpc}^{-1}$. Additionally, we investigate the transition redshift between the decelerating and accelerating cosmological phases through the GP reconstructed deceleration parameter. Furthermore, we reconstruct the model-independent evolution of the dark energy equation of state, and finally reconstruct the allowed $f(T)$ functions. As a result, the $\Lambda$CDM model lies inside the allowed region at 1$\sigma$ in all the examined kernels and datasets, however a negative slope for $f(T)$ versus $T$ is slightly favored.
25 citations
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TL;DR: In this article, a non-equilibrium thermodynamics based on adiabatic particle creation mechanism with the motivation of considering it as an alternative choice to explain the recent observed accelerating phase of the universe.
Abstract: The paper deals with non-equilibrium thermodynamics based on adiabatic particle creation mechanism with the motivation of considering it as an alternative choice to explain the recent observed accelerating phase of the universe. Using Friedmann equations, it is shown that the deceleration parameter ($q$) can be obtained from the knowledge of the particle production rate ($\Gamma$). Motivated from thermodynamical point of view, cosmological solutions are evaluated for the particle creation rates in three cosmic phases, namely, inflation, matter dominated and present late time acceleration. The deceleration parameter ($q$) is expressed as a function of the redshift parameter ($z$), and its variation is presented graphically. Also, statefinder analysis has been presented graphically in three different phases of the universe. Finally, two non-interacting fluids with different particle creation rates are considered as cosmic substratum, and deceleration parameter ($q$) is evaluated. It is examined whether more than one transition of $q$ is possible or not by graphical representations.
25 citations
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TL;DR: In this paper, the authors used recent 36 observational Hubble data (OHD) and their joint combination datasets to constrain anisotropic Bianchi type I (BI) dark energy (DE) model.
Abstract: We use recent 36 observational Hubble data (OHD) in the redshift range $0.07\leq z\leq 2.36$, latest \textgravedbl joint light curves\textacutedbl (JLA) sample, comprised of 740 type Ia supernovae (SNIa) in the redshift range $0.01\leq z \leq 1.30$, and their joint combination datasets to constrain anisotropic Bianchi type I (BI) dark energy (DE) model. To estimate model parameters, we apply Hamiltonian Monte Carlo technique. We also compute the covariance matrix for BI dark energy model by considering different datasets to compare the correlation between model parameters. To check the acceptability of our fittings, all results are compared with those obtained from 9 year WMAP as well as Planck (2015) collaboration. Our estimations show that at 68\% confidence level the dark energy equation of state (EOS) parameter for OHD or JLA datasets alone varies between quintessence and phantom regions whereas for OHD+JLA dataset this parameter only varies in phantom region. It is also found that the current cosmic anisotropy is of order $\sim10^{-3}$ which imply that the OHD and JLA datasets do not put tight constraint on this parameter. Therefore, to constraint anisotropy parameter, it is necessary to use high redshif dataset namely cosmic microwave background (CMB). Moreover, from the calculation of $p$-value associated with $\chi^{2}$ statistic we observed that non of the $\omega \mbox{BI}$ and flat $\omega\mbox{CDM}$ models rule out by OHD or JLA datasets. The deceleration parameter is obtained as $q=-0.46^{+0.89 +0.36}_{-0.41 -0.37}$, $q=-0.619^{+0.12 +0.20}_{-0.095 -0.24}$, and $q=-0.52^{+0.080 +0.014}_{-0.046 -0.15}$ for OHD, SNIa, and OHD+SNIa data respectively.
25 citations
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TL;DR: In this article, the Friedmann-Robertson-Walker (FRW) cosmological model in the presence of perfect fluid source in gravity was investigated and the physical and kinematical properties of the model were also discussed.
Abstract: In this paper, we investigate Friedmann-Robertson-Walker (FRW) cosmological model in the presence of perfect fluid source in \(f(R,T)\) gravity. We have used linearly varying deceleration parameter proposed by Akarsu and Dereli (Int. J. Theor. Phys. 51:612, 2012) and barotropic equation of state to obtain determinate solution of the field equations of the theory. Physical parameters of the model are determined and some physical and kinematical properties of the model are also discussed.
25 citations
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TL;DR: In this article, the authors constructed a cosmological model to explain the cosmology constant problem and found that the survival probability of unstable states is a decreasing function of the cosomological time and has the inverse power-like form.
Abstract: We construct the cosmological model to explain the cosmological constant problem. We built the extension of the standard cosmological model $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ by consideration of decaying vacuum energy represented by the running cosmological term. From the principles of quantum mechanics one can find that in the long-term behavior survival probability of unstable states is a decreasing function of the cosmological time and has the inverse powerlike form. This implies that cosmological constant ${\ensuremath{\rho}}_{\mathrm{vac}}=\mathrm{\ensuremath{\Lambda}}(t)={\mathrm{\ensuremath{\Lambda}}}_{\text{bare}}+\frac{\ensuremath{\alpha}}{{t}^{2}}$ where ${\mathrm{\ensuremath{\Lambda}}}_{\text{bare}}$ and $\ensuremath{\alpha}$ are constants. We investigate the dynamics of this model using dynamical system methods due to a link to the $\mathrm{\ensuremath{\Lambda}}(H)$ cosmologies. We have found the exact solution for the scale factor as well as the indicators of its variability like the deceleration parameter and the jerk. From the calculation of the jerk we obtain a simple test of the decaying vacuum in the Friedman-Robertson-Walker universe. Using astronomical data [SNIa, $H(z)$, CMB, BAO] we have estimated the model parameters and compared this model with the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model. Our statistical results indicate that the decaying vacuum model is a little worse than the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model. But the decaying vacuum cosmological model explains the small value of the cosmological constant today.
24 citations