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The impact of anisotropy on the Ricci dark energy cosmologies is investigated where it is assumed that the geometry of the universe is described by Bianchi type I (BI) metric. The main goal is to determine the astrophysical constraints on the model by using the current available data as type Ia supernovae (SNIa), the Baryon Acoustic Oscillation (BAO), and the Hubble parameter H (z) data. In this regard, a maximum likelihood method is applied to constrain the cosmological parameters. Combining the data, it is found out that the allowed range for the density parameter of the model stands in − 3. 6 × 1 0 − 3 ≲ Ω σ 0 ≲ − 2. 6 × 1 0 − 3 . With the help of the Supernova Legacy Survey (SNLS) sample, we estimate the possible dipole anisotropy of the Ricci dark energy model. Then, by using a standard χ 2 minimization method, it is realized that the transition epoch from early decelerated to current accelerated expansion occurs faster in Ricci dark energy model than Λ CDM model. The results indicate that the BI model for the Ricci dark energy is consistent with the observational data. [ABSTRACT FROM AUTHOR]

We investigate the effects of anisotropy on ghost dark energy model from the latest observational data. We have fitted our model with the present observational data including Supernovae type Ia (SNIa) and the Hubble expansion history H(z) datasets, and compare the results with the Λ CDM model. We test the possible dipole anisotropy of the ghost dark energy model, by using the Pantheon and the Supernova Legacy Survey (SNLS) sample. We also examine the behavior of different cosmological parameters such as Hubble parameter, equation of state (EoS) parameter and deceleration parameter of ghost dark energy model in an anisotropic universe. With the help of best fit results, we find that the EoS parameter represents quintessence era while a transition in the expansion history of universe from a deceleration phase to an accelerated one around z ≈ 1.42 with the 1 σ ′ confidence level. Finally we found that the presence of anisotropy improved the fit to observations with respect to that provided by an isotropic dark energy model. [ABSTRACT FROM AUTHOR]

We study the possibly existing anisotropy in the accelerating expansion Universe with various supernovae data, the baryon acoustic oscillation and the observational Hubble data. We present combined results from these probes, deriving constraints on the equation of state (EoS), w , of dark energy (DE) and its energy density in the Universe. We fit the cosmological parameters simultaneously employing the maximum likelihood analysis. By combining data and considering anisotropy effects, we find that the EoS of DE are w (0. 0 1 ≤ z ≤ 1. 7 5) = − 0. 9 9 8 ± 0. 0 5 6 , w (0 < z < 1) = − 1. 0 8 6 ± 0. 0 6 5 , w (0. 1 5 < z < 1. 1) = − 1. 0 9 6 ± 0. 1 2 3 and w (0. 0 1 < z < 2. 3) = − 1. 0 4 2 6 ± 0. 0 5 4 within 1 σ ′ confidence level. Finally, introducing an anisotropy appears to improve the fit to observations with respect to that provided by an isotropic w CDM model. [ABSTRACT FROM AUTHOR]

Abstract By using the supernovae type Ia (SNIa) data we study influence of the anisotropy (although low) on the evolution of the universe and compare ΛCDM model with 6 representative parametrizations of the recent Hubble expansion history H (z). To compare these models we use the maximum likelihood method for find that the best fit dynamical w (z) and q (z) obtained from the SNIa dataset. We have performed a comparative analysis of t hree SNIa datasets such as, the 194 SNIa (0 ≤ z ≤ 1.75), the Supernova Legacy Survey (SNLS) dataset (238 data points 0.15 < z < 1.1) a nd the most recent Pantheon sample (1048 data points 0.01 < z < 2.3). In particular we find the best fit value of ΛCDM model Ω σ 0 = 0.013 ± 0.008 , χ min 2 = 197.56 with 194 SNIa, Ω σ 0 = − 0.003 ± 0.033 , χ min 2 = 230.656 with 238 SNLS a nd Ω σ 0 = 0.011 ± 0.013 , χ min 2 = 1012.55 w ith 1048 Pantheon sample. The analysis shows that by considering the anisotropy, it leads to more best fit parameters in all models (except of SCDM) with SNIa data. We also use two statistical tests such as the usual χ min 2 / d o f and p-test to compare different dark energy models. According to both statistical tests and considering anisotropy, the ΛCDM model that is providing the best fit to ΛCDM of FRW model. An even better fit would result with an optimization of the data using effects of anisotropy from the beginning. [ABSTRACT FROM AUTHOR]

The 194 supernova Ia data and the effect of anisotropy are combined to reconstruct the dark energy equation of state parameter w (z) and the deceleration parameter q (z). Using the supernovae type Ia data, we evaluate the anisotropy effects (although low) on dark energy parametrization w = w 0 + w 1 z / (1 + z) and we compare the results with Λ CDM model. Present supernova observations are analyzed using a standard χ 2 method and the minimal χ 2 values obtained for each model are compared. We confirm the difficulty of discriminating between these models using present SNIa data only. By means of the maximum likelihood method, we find that the best-fit dynamical w (z) and q (z) parameters (w 0 , w 1) are obtained from the SNIa dataset. In particular, we find the best-fit values of Λ CDM model ( Ω σ 0 = 0.013, χ min 2 = 197.559) for Ω m 0 = 0.3 and ( Ω σ 0 = 0.02, χ min 2 = 196.983) for Ω m 0 = 0.27. Finally, we found that the presence of anisotropy is confirmed in mentioned models via SNIa dataset. [ABSTRACT FROM AUTHOR]

We study effects of anisotropy (although low) on the ghost and generalized ghost dark energy (DE) models in the framework of fractal cosmology. We obtain the equation of state parameter, ω DE , the deceleration parameter, and the evolution equation of the ghost and generalized ghost dark energy. We find that, in both models, ω DE cannot cross the phantom line and eventually the universe approaches a de-Sitter phase of expansion. We show that the anisotropy effects on ghost and generalized ghost dark energy (GDE) in fractal cosmology correspond to Λ CDM limit on the statefinder plane. We evaluate the anisotropy effects on both the linear perturbation and the spherical collapse from the DE models and compare them with the results of the DE of the Friedmann–Robertson–Walker and Λ CDM models. We also show that in ghost and generalized ghost cosmologies, the growth factor g (a) rise front the values for an Λ CDM universe. Finally, we constrain the model parameters by using the maximum likelihood analysis and a combined dataset of baryon acoustic oscillation (BAO) and OHD. [ABSTRACT FROM AUTHOR]