Quintessence or Phantom: Study of scalar field dark energy models
  through a general parametrization of the Hubble parameter
  In this work we propose a simple general parametrization scheme of the Hubble
parameter for the scalar field dark energy models. In our approach it is
possible to incorporate both the quintessence and phantom scalar field in a
single analytical scheme and write down relevant cosmological parameters which
are independent of the nature of the scalar field. A general condition for the
phantom barrier crossing has also been obtained. To test this approach, a well
behaved parametrization of the normalized Hubble parameter has been considered
and a wide variety of observational data like CMB data, Supernovae data, BAO
data etc. has been used to constraint the various cosmological parameters. It
has been found that data prefer the present value of the equation of state of
the dark energy to be in the phantom domain. One interesting outcome of this
analysis is that although the current value of the dark energy equation of
state is phantom in nature, a phantom crossing of the EOS has taken place in
the recent past. We have also carried out the Bayesian model comparison between
$\Lambda CDM$ model and the proposed model which indicates that this model is
favored by data as compared to $\Lambda CDM$ model.
