Observational constraints to a unified cosmological model

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.