arXiv subjects

Z. Davari

Publications and source records attributed to Z. Davari.

4 recordsLinked to original sources

arXiv2025

Observational constraints on New Tsallis holographic energy in Rastall theory

The cosmological implications of New Tsallis holographic dark energy (NTHDE) in Rastall theory have been studied. Using the data set that includes DESI BAO (DR2), PantheonPlus SNe Ia, H(z) measurements, and BBN and the MCMC analysis, the key cosmological and model-specific parameters are constrained. The result is compared with that of the {\Lambda}CDM model indicating that in addition to providing a viable dynamical dark energy framework, predictions for H(z) are slightly more consistent with intermediate-redshift observations. Generally, the model remains compatible with current data and offers testable deviations from {\Lambda}CDM for upcoming surveys. It is also seen that when the energy density of quantum fields in vacuum, exposed by NTHDE, is combined with the Rastall correction term to the general relativity, a plausible candidate for dynamical dark energy is obtained that mimic the current value of the dark energy density parameter reported in the {\Lambda}CDM model. The latter cannot be repeated by NTHDE alone. The study also confirms previous theoretical and observational constraints on the Rastall parameter obtained by focusing on the thermodynamics, early universe, pulsars, and the early-type galaxies.

astro-ph.CO↗

arXiv2024

Observational constraints on FLRW, Bianchi type I and V brane models

This study explores the compatibility of Covariant Extrinsic Gravity (CEG) with current cosmological observations. We employ the chi-square statistic and Markov Chain Monte Carlo (MCMC) methods to fit the FLRW and Bianchi type-I and V brane models to the latest datasets, including Hubble, Pantheon+ Supernova samples, Big Bang Nucleosynthesis (BBN), Baryon Acoustic Oscillations (BAO), and the structure growth rate, $f\sigma_8(z)$. Parameters for FLRW universe consist $\left(\Omega^{\text{(b)}}_0, \Omega^{\text{(cd)}}_0, \Omega^{\text{(k)}}_0, H_0, \gamma, \sigma_8\right)$, while for the Bianchi model are $\left(\Omega^{\text{(b)}}_0, \Omega^{\text{(cd)}}_0, \Omega^{{(\beta)}}_0, H_0, \gamma, \Omega^{(\theta)}_0, \sigma_8\right)$. We determine the best values for cosmological parameters. For the FLRW model, these values depend on the sign of $\gamma$: $\gamma > 0$ yields $\gamma =0.00008^{+0.00015}_{-0.00011}$, and $\Omega^{\text{(k)}}_0=0.014^{+0.024}_{-0.022}$ and $\gamma < 0$ leads to $\gamma =-0.0226^{+0.0054}_{-0.0062}$, and $\Omega^{\text{(k)}}_0=0.023^{+0.039}_{-0.041}$. In both cases $\Omega^{\text{(k)}}_0>0$ represents a closed universe. Similarly, for the Bianchi type-V brane model, the parameter values vary with the sign of $\gamma$, resulting in $\gamma = 0.00084^{+0.00019}_{-0.00021}$, $\Omega^{(\beta)}_0 =0.0258^{+0.0052}_{-0.0063} $, and $\Omega^{\theta}_0(\times 10^{-5} ) = 4.19^{+0.67}_{-0.75}$ (as with the density parameter of stiff matter) for $\gamma > 0$, and $\gamma = -0.00107^{+0.00019}_{-0.00020}$, $\Omega^{(\beta)}_0 = 0.0259^{+0.0050}_{-0.0062} $, and $\Omega^{\theta}_0(\times 10^{-5} ) = 4.17^{+0.91}_{-0.98}$ for $\gamma < 0$. In both cases $\Omega^{(\beta)}_0>0$, which represents the Bianchi type-V, because in the Bianchi type-I, $\beta=0$. Utilizing these obtained best values, we analyze the behavior of key cosmological parameters.

gr-qc↗

arXiv2024

Cosmological constraints on dark energy parametrizations after DESI 2024: Persistent deviation from standard $\Lambda$CDM cosmology

In this work, we present a study on cosmological constraints of dark energy (DE) parametrizations after the observations of Dark Energy Spectroscopic Instruments (DESI) for Baryon Acoustic Oscillations (BAO) in 2024, suggesting potential deviations from the standard flat-$\Lambda$CDM cosmology. This study aims to put observational constraints on equation of state (EoS) parametrizations beyond the standard $\Lambda$CDM model using DESI BAO 2024 data, Cosmic Microwave Background (CMB) anisotropy observations 2018, and various Supernovae type Ia (SNIa) compilations: PantheonPlus, Union3, and Dark Energy Survey 5-year photometrically classified SNIa (DES-SN5YR). Our main goal is to validate the result of DESI collaborations \cite{DESI:2024mwx} in the context of some parametrizations beyond the Chevallier-Polarski-Linder (CPL) approximation known as Barboza-Alcaniz (BA) and Pad\'e parametrizations. These investigations allow us to examine the potential biases in the results presented by DESI collaborations with respect to CPL parametrization. By comparing our findings using BA and Pad\'e parametrizations to the CPL case, we indicate that the deviation from $w_{\Lambda} = -1.0$, observed in the CPL parametrization, is also evident in the BA and Pad\'e parametrizations.

astro-ph.CO↗

arXiv2016

Agegraphic dark energy: growth index and cosmological implications

We study the main cosmological properties of the agegraphic dark energy model at the expansion and perturbation levels. Initially, using the latest cosmological data we implement a joint likelihood analysis in order to constrain the cosmological parameters. Then we test the performance of the agegraphic dark energy model at the perturbation level and we define its difference from the usual $Λ$CDM model. Within this context, we verify that the growth index of matter fluctuations depends on the choice of the considered agegraphic dark energy (homogeneous or clustered). In particular, assuming a homogeneous agegraphic dark energy we find, for the first time, that the asymptotic value of the growth index is $γ\approx 5/9$, which is close to that of the usual $Λ$ cosmology, $γ^{(Λ)} \approx 6/11$. Finally, if the distribution of dark energy is clustered then we obtain $γ\approx 1/2$ which is $\sim 8\%$ smaller than that of the $Λ$CDM model.

astro-ph.CO↗