Bias of reconstructing the dark energy equation of state from the Pade cosmography
Abstract
Pade cosmography has been widely used to probe the cosmic evolution and to investigate the nature of dark energy. In this paper, we find that the Pade approximant can describe the cosmic evolution better than the standard cosmography, and if the luminosity distance dL(z) described by the Pade approximant is used to reconstruct the dark energy equation of state w(z), then the reconstructed w(z) will approach a constant, i.e. 1/3 or 0, when the redshift is very high. This result is general since it is independent of the coefficients in the Pade approximant and the value of the present dimensionless matter density parameter. This intrinsic character will bias the w(z) reconstruction and lead to misconception of the property of dark energy. Therefore, one must exercise caution in investigating the property of dark energy from Pade cosmography when the high redshift data, i.e. z>2, are included.
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