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Register a new userObservational constraints to a unified cosmological model
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We propose a phenomenological unified model for dark matter and dark energy based on an equation of state parameter $w$ that scales with the $arctan$ of the redshift. The free parameters of the model are three constants: $Omega_{b0}$, $alpha$ and $beta$. Parameter $alpha$ dictates the transition rate between the matter dominated era and the accelerated expansion period. The ratio $beta / alpha$ gives the redshift of the equivalence between both regimes. Cosmological parameters are fixed by observational data from Primordial Nucleosynthesis (PN), Supernovae of the type Ia (SNIa), Gamma-Ray Bursts (GRB) and Baryon Acoustic Oscillations (BAO). The calibration of the 138 GRBs events is performed using the 580 SNIa of the Union2.1 data set and a new set of 79 high-redshift GRBs is obtained. The various sets of data are used in different combinations to constraint the parameters through statistical analysis. The unified model is compared to the $Lambda$CDM model and their differences are emphasized.
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Over the last years some interest has been gathered by $f(Q)$ theories, which are new candidates to replace Einsteins prescription for gravity. The non-metricity tensor $Q$ allows to put forward the assumption of a free torsionless connection and, consequently, new degrees of freedom in the action are taken into account. This work focuses on a class of $f(Q)$ theories, characterized by the presence of a general power-law term which adds up to the standard (linear in) $Q$ term in the action, and on new cosmological scenarios arising from them. Using the Markov chain Montecarlo method we carry out statistical tests relying upon background data such as Type Ia Supernovae luminosities and direct Hubble data (from cosmic clocks), along with Cosmic Microwave Background shift and Baryon Acoustic Oscillations data. This allows us to perform a multifaceted comparison between these new cosmologies and the (concordance) $Lambda$CDM setup. We conclude that, at the current precision level, the best fits of our $f(Q)$ models correspond to values of their specific parameters which make them hardly distinguishable from our General Relativity echantillon, that is $Lambda$CDM.
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 flat 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.
In the paper, we consider two models in which dark energy is coupled with either dust matter or dark matter, and discuss the conditions that allow more time for structure formation to take place at high redshifts. These models are expected to have a larger age of the universe than that of $Lambda$CDM [universe consists of cold dark matter (CDM) and dark energy (a cosmological constant, $Lambda$)], so it can explain the formation of high redshift gravitationally bound systems which the $Lambda$CDM model cannot interpret. We use the observational Hubble parameter data (OHD) and Hubble parameter obtained from cosmic chronometers method ($H(z)$) in combination with baryon acoustic oscillation (BAO) data to constrain these models. With the best-fitting parameters, we discuss how the age, the deceleration parameter, and the energy density parameters evolve in the new universes, and compare them with that of $Lambda$CDM.
We consider an interacting field theory model that describes the interaction between dark energy - dark matter interaction. Only for a specific interaction term, this interacting field theory description has an equivalent interacting fluid description. For inverse power law potentials and linear interaction function, we show that the interacting dark sector model is consistent with $textit{four cosmological data sets}$ -- Hubble parameter measurements (Hz), Baryonic Acoustic Oscillation data (BAO), Supernova Type Ia data (SN), and High redshift HII galaxy measurements (HIIG). More specifically, these data sets prefer a negative value of interaction strength in the dark sector and lead to the best-fit value of Hubble constant $H_0 = 69.9^{0.46}_{1.02}$ km s$^{-1}$ Mpc$^{-1}$. Thus, the interacting field theory model $textit{alleviates the Hubble tension}$ between Planck and these four cosmological probes. Having established that this interacting field theory model is consistent with cosmological observations, we obtain quantifying tools to distinguish between the interacting and non-interacting dark sector scenarios. We focus on the variation of the scalar metric perturbed quantities as a function of redshift related to structure formation, weak gravitational lensing, and the integrated Sachs-Wolfe effect. We show that the difference in the evolution becomes significant for $z < 20$, for all length scales, and the difference peaks at smaller redshift values $z < 5$. We then discuss the implications of our results for the upcoming missions.
We constrain the contribution of tensor-mode perturbations with free $n_t$ in the models with dynamical dark energy with the barotropic equation of state using Planck-2015 data on CMB anisotropy, polarization and lensing, BICEP2/Keck Array data on B-mode polarization, power spectrum of galaxies from WiggleZ and SN Ia data from the JLA compilation. We also investigate the uncertainties of reconstructed potential of the scalar field dark energy.
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