Probing the Cosmic Dawn using the redshifted 21-cm bispectrum

In the evolutionary history of our Universe, the Cosmic Dawn and Epoch of reionization (CD-EoR) is the period when the formation and evolution of the  very first luminous sources took place. These first sources transitioned the state of the Universe from cold and neutral to a fully heated and ionized one, together with introducing a high level of non-Gaussianity in the heating and ionization field. The CD-EoR 21-cm radiation from the abundant neutral hydrogen atom (HI) in the inter-galactic medium (IGM) is the direct tracer of heating and ionization processes in the IGM during this era. It thus carries the intrinsic non-Gaussian information present in the field. The power spectrum, which is one of the widely used and conventional statistics as a probe of the CD-EoR 21-cm signal in the current observations of this signal, cannot capture this non-Gaussianity. The bispectrum, being a potential probe of this non-Gaussianity, provides an opening for a comprehensive and correct interpretation of this signal. We, for the first time, explore how the bispectrum, probing the non-Gaussianity, can provide better insights into IGM physics during CD-EoR. This will help us in interpreting the future observations of the CD-EoR 21-cm signal using the upcoming Square Kilometer Array (SKA) once the interferometric detection of  this signal has been made possible.