New general parametrization of quintessence fields and its observational
  constraints
  We present a new parameterization of quintessence potentials for dark energy
based directly upon the dynamical properties of the equations of motion. Such
parameterization arises naturally once the equations of motion are written as a
dynamical system in terms of properly defined polar variables. We have
identified two different classes of parameters, and we dubbed them as dynamical
and passive parameters. The dynamical parameters appear explicitly in the
equations of motion, but the passive parameters play just a secondary role in
their solutions. The new approach is applied to the so-called thawing
potentials and it is argued that only three dynamical parameters are sufficient
to capture the evolution of the quintessence fields at late times. This work
reconfirms the arbitrariness of the quintessence potentials as the recent
observational data fail to constrain the dynamical parameters.
