Curvature dark energy reconstruction through different cosmographic distance definitions. Issue 7 (25th July 2014) - Capozziello, Salvatore
Abstract In the context of f(R) gravity, dark energy is a geometrical fluid with negative equation of state. Since the function f(R) is not known a priori, the need of a model independent reconstruction of its shape represents a relevant technique to determine which f(R) model is really favored with respect to others. To this aim, cosmography is related to a generic f(R) and its derivatives in order to provide a model‐independent investigation at redshift z∼0. The analysis is based on the use of three different cosmological distance definitions, in order to alleviate the duality problem, i.e. the problem of which cosmological distance to use with specific cosmic data sets. Therefore, the luminosity, dL, flux, dF, and angular, dA, distances are considered and numerical constraints by the Union 2.1 supernovae compilation and measurement of baryonic acoustic oscillations, at zBAO=0.35 are found. It was noticed that all distances reduce to the same expression, i.e. dL;F;A∼1H0z, at first order. Thus, to fix the cosmographic series of observables, the initial value of H0 was imposed by fitting H0 through supernovae only, in the redshift regime z<0.4. The pressure of curvature dark energy fluid was found to be slightly lower than the one related to the cosmological constant. This indicates that a possible evolving curvature dark energy realistically fills the current universe. Moreover, the combined use of dL, dF and dA shows that the sign of the acceleration parameter agrees with theoretical bounds, while its variation, namely the jerk parameter, is compatible with j0>1. Finally, the functional form of f(R) is infered by means of a truncated polynomial approximation, in terms of fourth order scale factor a(t).