Dark energy constraints from the 21~cm intensity mapping surveys with
  SKA1
  Understanding the nature of dark energy is one of the most outstanding
problems in cosmology at present. In last twenty years, cosmological
observations related to SNIa, Cosmic Microwave Background Radiation, Baryon
Acoustic Oscillations etc, have put stringent constraints on the the dark
energy evolution, still there is enough uncertainty in our knowledge about dark
energy that demands new generation of cosmological observations.
Post-reionization neutral hydrogen 21 cm intensity mapping surveys are one of
the most promising future cosmological observations that have the potential to
map the cosmological evolution from dark ages till present time with
unprecedented accuracy and Square Kilometer Array (SKA) is one of the most
sensitive instruments to measure the post-reionization 21 cm signal. In this
work, we study the future dark energy constraints using post-reionization 21 cm
intensity mapping power spectra with SKA1-mid specifications. We use three
different parametrizations for dark energy equation of state (EoS) including
the widely used CPL one. To generate simulated data, we use to two fiducial
models: the concordance $\Lambda$CDM and the best fit CPL model for
Planck+SNIa+BAO+HST. Our study shows that SKA1-mid alone has the potential to
reach the present accuracy for combined Planck+SNIa+BAO+HST to constrain the
dark energy behaviour. Whether dark energy is phantom or non-phantom or whether
it exhibits phantom crossing, we may potentially address such questions with
SKA1-mid. We also show that it is crucial to choose the correct parametrization
for dark energy equation of state as some parametrizations are better than
others to constrain the dark energy behaviour. Specifically, as observed in
this study, the widely used CPL parametrization may not give the best
constraint for dark energy behaviour.
