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.