In this work, we use an observational approach and dynamical system analysis to study the cosmological model recently proposed by Saridakis (2020), which is based on the modification of the entropy-area black hole relation proposed by Barrow (2020).
The Friedmann equations governing the dynamics of the Universe under this entropy modification can be calculated through the gravity-thermodynamics conjecture. We investigate two models, one considering only a matter component and the other including matter and radiation, which have new terms compared to the standard model sourcing the late cosmic acceleration. A Bayesian analysis is performed in which we use five cosmological observations (observational Hubble data, type Ia supernovae, HII galaxies, strong lensing systems, and baryon acoustic oscillations) to constrain the free parameters of both models. From a joint analysis, we obtain constraints that are consistent with the standard cosmological paradigm within $2sigma$ confidence level. In addition, a complementary dynamical system analysis using local and global variables is developed which allows obtaining a qualitative description of the cosmology. As expected, we found that the dynamical equations have a de Sitter solution at late times.
The accelerated expansion of the Universe is one of the main discoveries of the past decades, indicating the presence of an unknown component: the dark energy. Evidence of its presence is being gathered by a succession of observational experiments wi
th increasing precision in its measurements. However, the most accepted model for explaining the dynamic of our Universe, the so-called Lambda cold dark matter, face several problems related to the nature of such energy component. This has lead to a growing exploration of alternative models attempting to solve those drawbacks. In this review, we briefly summarize the characteristics of a (non-exhaustive) list of dark energy models as well as some of the most used cosmological samples. Next, we discuss how to constrain each models parameters using observational data. Finally, we summarize the status of dark energy modeling.
Motivated by two seminal models proposed to explain the Universe acceleration, this paper is devoted to study a hybrid model which is constructed through a generalized Chaplygin gas with the addition of a bulk viscosity. We call the model a Viscous G
eneralized Chaplygin Gas (VGCG) and its free parameters are constrained through several cosmological data like the Observational Hubble Parameter, Type Ia Supernovae, Baryon Acoustic Oscillations, Strong Lensing Systems, HII Galaxies and using Joint Bayesian analysis. In addition, we implement a Om-diagnostic to analyze the VGCC dynamics and its difference with the standard cosmological model. The hybrid model shows important differences when compared with the standard cosmological model. Finally, based on our Joint analysis we find that the VGCG could be an interesting candidate to alleviate the well-known Hubble constant tension.
In this paper, we study a particular modified gravity Equation of State, the so-called Jaime-Jaber-Escamilla, that emerges from the first gravity modified action principle and can reproduce three cosmological viable $f(R)$ theories: the Starobinsky,
Hu-Sawicki, and Exponential models . This EoS is a suitable candidate to reproduce the dynamical dark energy behaviour already reconstructed by the current data sets. Based on the joint statistical analysis, we found that our results are still in good agreement (within $1sigma$) with the $Lambda$CDM, while at perturbative level we notice that the matter power spectrum normalisation factor $sigma_8$ shows an agreement with SDSS and SNeIa+IRAS at 1-$sigma$ for the Starobinsky model and with SDSS-vec for the Hu & Sawicki and Exponential models. Furthermore, we found that for the $H_0$ values, Starobinsky and Hu & Sawicki show the least tension in comparison with PL18 TT. All these aspects cannot be observed textit{directly} from other alternatives theories, were a equation of state is difficult to compute analytically.
In this work we explore an alternative phenomenological model to Chaplygin gas proposed by H. Hova et. al., consisting on a modification of a perfect fluid, to explain the dynamics of dark matter and dark energy at cosmological scales immerse in a fl
at or curved universe. Adopting properties similar to a Chaplygin gas, the proposed model is a mixture of dark matter and dark energy components parameterized by only one free parameter denoted as $mu$. We focus on contrasting this model with the most recent cosmological observations of Type Ia Supernovae and Hubble parameter measurements. Our joint analysis yields a value $mu = 0.843^{+0.014}_{-0.015},$ ($0.822^{+0.022}_{-0.024}$) for a flat (curved) universe. Furthermore, with these constraints we also estimate the deceleration parameter today $q_0=-0.67 pm 0.02,(-0.51pm 0.07)$, the acceleration-deceleration transition redshift $z_t=0.57pm 0.04, (0.50 pm 0.06)$, and the universe age $t_A = 13.108^{+0.270}_{-0.260},times (12.314^{+0.590}_{-0.430}),$Gyrs. We also report a best value of $Omega_k = 0.183^{+0.073}_{-0.079}$ consistent at $3sigma$ with the one reported by Planck Collaboration. Our analysis confirm the results by Hova et al, this Chaplygin gas-like is a plausible alternative to explain the nature of the dark sector of the universe.
