  The 21 cm signal appears to be a treasure trove to provide an insight into
the period when the first generation of luminous objects formed in the
Universe. Hydrogen is the predominating fraction of the total baryonic matter
during cosmic dawn (CD). Therefore, it is convenient and advantageous to study
physics during CD using the 21 cm signal. The presence of any exotic source of
energy can inject energy into the intergalactic medium (IGM) and heat the gas.
Subsequently, it can modify the absorption amplitude in the global 21 cm
signal. This feature can provide a robust bound on such sources of energy
injection into the IGM gas.
