Cosmographic parameters in model-independent approaches

Abstract

Cosmographic approach, a Taylor expansion of the Hubble function, has been used as a model-independent method to investigate the evolution of the universe in the presence of cosmological data. Apart from possible technical problems like the radius of convergence, there is an ongoing debates about the tensions appear when one investigates some high redshift cosmological data. In this work, we consider two common data sets namely SNIa (Pantheon sample) and the Hubble data to investigate advantages and disadvantages of the cosmographic approach. To do this, we obtain the evolution of cosmographic functions using cosmographic method as well as two other well known model-independent approaches namely, the Gaussian process and the Genetic algorithm. We also assume ΛCDM model as concordance model to compare the results of mentioned approaches. Our results indicate that the results of cosmography comparing with the other approaches, are not exact enough. Considering the Hubble data which is less certain, the results of q 0 and j 0 obtained in cosmography, provides a tension at more than 3σ away from the best result of ΛCDM. Assuming both of data samples in different approaches we show that the cosmographic approach, because of providing some biased results, is not the best approach for reconstruction of cosmographic functions, especially at higher redshifts.