Abstract
We study the dynamical properties of dark energy based on a large family of Padé parameterizations for which the dark energy density evolves as the ratio between two polynomials in the scale factor of the universe. Using the latest cosmological data we perform a standard likelihood analysis in order to place constraints on the main cosmological parameters of different Padé models. We find that the basic cosmological parameters, namely ({varOmega _{m0}},h,{sigma _{8}}) are practically the same for all Padé parametrizations explored here. Concerning the free parameters which are related to dark energy we show that the best-fit values indicate that the equation of state parameter at the present time is in the phantom regime (w<-1); however, we cannot exclude the possibility of w>-1 at 1sigma level. Finally, for the current family of Padé parametrizations we test their ability, via AIC, BIC and Jeffreys’ scale, to deviate from varLambda CDM cosmology. Among the current Padé parametrizations, the model which contains two dark energy parameters is the one for which a small but non-zero deviation from varLambda CDM cosmology is slightly allowed by the AIC test. Moreover, based on Jeffreys’ scale we show that a deviation from varLambda CDM cosmology is also allowed and thus the possibility of having a dynamical dark energy in the form of Padé parametrization cannot be excluded.
Highlights
An alternative avenue to overcoming the above problems is to introduce a dynamical dark energy (DE), wherein the density of DE is allowed to evolve with cosmic time [24–30]
The family of Padé models and the corresponding free parameters used here are shown in Tables 2 and 3 respectively
The evolution of dark energy is treated within the context of a Padé parameterization, which can be seen as an expansion around the usual ΛCDM cosmology
Summary
An alternative avenue to overcoming the above problems is to introduce a dynamical DE, wherein the density of DE is allowed to evolve with cosmic time [24–30]. The first choice is to consider a DE fluid where the equation of state parameter varies with redshift, w(z). In these kinds of studies the EoS parameter can be written either as a first-order Taylor expansion around a(z) = 1 [31,32] or as a Padé parametrization [33–36], where the corresponding free parameters are fitted by the cosmological data [37–44]. One may use parametric criteria toward reconstructing directly the evolution of DE density ρde(z) [50–52] and the potential of the scalar field [53]. Considering an isotropic and homogeneous universe, driven by radiation, non-relativistic matter and dark energy with equation of state, PQ = w(a)ρQ < 0, the first Friedman equation is given by H2 =.
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