Abstract
We propose a phenomenological unified model (UM) 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: Ωb0, α and β. Parameter α dictates the transition rate between the matter dominated era and the accelerated expansion period. The ratio β/α 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 (GRBs) and baryon acoustic oscillations (BAOs). The calibration of the 138 GRB events is performed using the 580 SNIa of the Union2.1 data set and a new set of 79 high-redshift GRB is obtained. The various sets of data are used in different combinations to constraint the parameters through statistical analysis. The UM is compared to the ΛCDM model and their differences are emphasized.
Highlights
The recent technological improvement in the space observations deeply altered Cosmology
The Unified Model (UM) is a dynamical model developed from a specific functional form chosen for the parameter w of the equation of state p = wρ, where p is the pressure related to the cosmic component of density ρ: w is given in terms of the arctan function
Our framework will be a flat universe filled with baryonic matter and a unified component of dark matter and dark energy
Summary
The recent technological improvement in the space observations deeply altered Cosmology. The resulting ΛCDM cosmological model [17] is robust when confronted to observational data, it is not a comfortable solution mainly due to the lack of a clear interpretation of the physical meaning of Λ in terms of the known fundamental interactions This very fact relegates Λ to the mysterious “dark sector” of the universe. The UM is a dynamical model developed from a specific functional form chosen for the parameter w of the equation of state p = wρ, where p is the pressure related to the cosmic component of density ρ: w is given in terms of the arctan function This way, the universe filled with the unified fluid passes smoothly from a matter-like behavior (w 0) to a dark-energy-like dynamics (w −1).
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