Deceleration parameter

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

Comparison of piecewise-constant methods for dark energy

Abstract: We compare four different methods that can be used to analyze the type Ia supernovae (SnIa) data, ie to use piecewise-constant functions in terms of: the dark energy equation of state $w(z)$, the deceleration parameter $q(z)$, the Hubble parameter $H(z)$ and finally the luminosity distance $d_L$. These four quantities cover all aspects of the accelerating Universe, ie the phenomenological properties of dark energy, the expansion rate (first and second derivatives) of the Universe and the observations themselves. For the first two cases we also perform principal component analysis (PCA) so as to decorrelate the parameters, while for the last two cases we use novel analytic expressions to find the best-fit parameters. In order to test the methods we create mock SnIa data (2000 points, uniform in redshift $z\in[0,1.5]$) for three fiducial cosmologies: the cosmological constant model ($\Lambda$CDM), a linear expansion of the dark energy equation of state parameter $w(a)=w_0+w_a(1-a)$ and the Hu-Sawicki $f(R)$ model. We find that if we focus on the two mainstream approaches for the PCA, i.e. $w(z)$ and $q(z)$, then the best piecewise-constant scheme is always $w(z)$. Finally, to our knowledge the piecewise-constant method for $H(z)$ is new in the literature, while for the rest three methods we present several new analytic expressions.

Perfect Fluid Lrs Bianchi I With Time Varying Constants

Abstract: It is investigated the behaviour of the “constants” G, c and Λ in the framework of a perfect fluid LRS Bianchi I cosmological model. It has been taken into account the effects of a c-variable into the curvature tensor. Two exact cosmological solutions are investigated, arriving t the conclusion that if q < 0 (deceleration parameter) then G, c are growing functions on time t while Λ is a negative decreasing function on time.

Anisotropic Dark Energy Bianchi Type-II Cosmological Models in Lyra Geometry

Abstract: The spatially homogeneous and totally anisotropic Bianchi type-II cosmological model has been discussed in general relativity in the presence of a hypothetical anisotropic dark energy fluid with constant deceleration parameter within the frame work of Lyra’s manifold with uniform and time varying displacement field vector. With the help of special law of variation for Hubble’s parameter proposed by Bermann (Nuovo Cimento 74B:182, 1983) a dark energy cosmological model is obtained in this theory. We use the power law relation between average Hubble parameter H and average scale factor R to find the solution. The assumption of constant deceleration parameter leads to two models of universe, i.e. power law model and exponential model. Some physical and kinematical properties of the model are also discussed.

Scenario of a two-fluid FRW cosmological model with dark energy

Abstract: In this paper we carry out an investigation of the equation of state parameter for dark energy in the spatially homogeneous and isotropic Friedmann-Robertson-Walker (FRW) model with barotropic fluid and dark energy. To get a deterministic model, we have assumed that the deceleration parameter (q) is a linear function of the Hubble parameter (H), i.e., $q=\alpha + \beta H$ , which yields the scale factor $a= e^{\frac{1}{\beta}\sqrt{2\beta t+k_{1}}}$ , where $k_{1}$ is constant. The equation of state parameter for dark energy is a decreasing function of cosmic time in both interacting and non-interacting cases, and is always varying in the quintessence region for all cases. We have also discussed the jerk parameter for our models, and its value approaches that of the $\Lambda$ CDM model at late times.

Particle production and universal thermodynamics

Abstract: In the present work, particle creation mechanism has been employed to the Universe as a thermodynamical system. The Universe is considered to be a spatially flat FRW model and cosmic fluid is chosen as a perfect fluid with a barotropic equation of state— $$p=(\gamma -1)\rho $$ . By proper choice of the particle creation rate, expressions for the entropy and temperature have been determined at various stages of evolution of the Universe. Finally, using the deceleration parameter q as a function of the redshift parameter z based on recent observations, the particle creation rate has been evaluated and its variation at different epochs have been shown graphically.