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 $be
ta$. 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.
We discuss a way to obtain information about higher dimensions from observations by studying a brane-based spherically symmetric solution. The three classic tests of General Relativity are analyzed in details: the perihelion shift of the planet Mercu
ry, the deflection of light by the Sun, and the gravitational redshift of atomic spectral lines. The braneworld version of these tests exhibits an additional parameter $b$ related to the fifth-coordinate. This constant $b$ can be constrained by comparison with observational data for massive and massless particles.
