State finder and Om diagnostics in modified and generalised Chaplygin gas from recent data

A modified and generalised Chaplygin gas (MCG, [Formula: see text] and GCG, [Formula: see text]) has been separately chosen here as a constituent of the universe. Concept of state finder and Om diagnostics are introduced to track the dark energy in the models. Here, observed Hubble data (OHD) and binned Pantheon data of supernovae are used to determine the best-fit equation-of-state (EoS) parameters of these models and these are compared with the [Formula: see text]CDM model. The best-fit value and expected values of cosmological jerk parameter [Formula: see text], snap parameter [Formula: see text] are determined, which are close to each other. A plot of [Formula: see text] with red-shift, with themselves, as well as with deceleration parameter [Formula: see text], shows the evolution of the universe and its possible future. Variations of [Formula: see text] and EoS parameter [Formula: see text] with red-shift show acceleration–deceleration phase transition in the recent past. Lastly, the state finder pair [Formula: see text] and Om diagnostic have been utilized to discriminate the models.

Non-parametric reconstruction of the cosmological jerk parameter

The cosmological jerk parameter j is reconstructed in a non-parametric way from observational data independent of a fiducial cosmological model. The Cosmic Chronometer data as well as the Supernovae data (the Pantheon compilation) are used for the purpose. The reconstructed values are found to be consistent with the standard $$\Lambda $$ Λ CDM model within the $$2\sigma $$ 2 σ confidence level. The model dependent sets like Baryon Acoustic Oscillation and the CMB Shift data are also included thereafter, which does not significantly help in improving or de-proving the confidence level in favour of $$\Lambda $$ Λ CDM. The deceleration parameter q is also reconstructed from the same data sets. This is used to find the effective equation of state parameter for the model independent datasets only. $$\Lambda $$ Λ CDM model is excluded for some part of the evolution in $$1\sigma $$ 1 σ , but is definitely included in $$2\sigma $$ 2 σ in the domain ($$0 \le z \le 2.36$$ 0 ≤ z ≤ 2.36 ) of all the reconstructions.

An approach to investigate stability, cosmography and the dark energy dipole: A case study of cosmological models in R1+ϵ

In this paper, in a new approach, we study the stability of the dynamical system (DS) of [Formula: see text] in terms of two significant cosmological parameters, deceleration parameter and jerk parameter [Formula: see text]. Other cosmographic parameters such as [Formula: see text] have been obtained in terms of these two parameters. We have obtained critical points ([Formula: see text]), the best fitted current values of cosmographic parameters ([Formula: see text]), best value for model parameter [Formula: see text] and best trajectory of dynamics of system in phase space by simultaneously solving the DS and best fitting the parameter by the SNIa data. By defining modified redshift in anisotropic cosmological model as [Formula: see text] (where [Formula: see text] is a magnitude of anisotropy, [Formula: see text] is direction of privileged axis and [Formula: see text] is the direction of each SNe Ia sample to galactic coordinates), the luminosity distance has been obtained in terms of modified redshift using cosmography method. Using union 2 data, we have found the direction of privileged axis in the galactic coordinate. The results show that the magnitude of anisotropy is about [Formula: see text] and the direction of privileged axis is [Formula: see text]. Also, our results are consistent with other studies in [Formula: see text] confidence level.

DARK ENERGY FROM A POSITIVE JERK PARAMETER

In this paper, we demonstrate that the variation of acceleration, namely the jerk parameter j, could give hints for determining the dark energy equation of state (EoS). In particular, it is possible to show that a viable cosmological model is compatible with a constant jerk, here conventionally rewritten as j = 1+ϵ, with ϵ > 0 representing a departure from the ΛCDM model. This suggests that the cosmological constant could be seen as a limiting case of a more general dark energy model. We use the most recent union 2.1 compilation of supernovae Ia, showing at 1σ confidence level, that j is compatible with the condition j ≥ 1. In doing so, we infer a corresponding cosmological model, viable with a negative acceleration parameter, in the observed range -1 < q0 < 0.