Addressing the self-interaction for ELDER dark matter from the 21-cm signal

The self-interacting dark matter can affect various cosmological processes. Such interactions can be number conserving (\emph{e.g.} $2 \rightarrow 2$) or number violating (\emph{e.g.} $3 \rightarrow 2,\,4 \rightarrow 2$ etc.). The latter processes where three (or more) dark matter particles undergo self-annihilation/scattering to produce less number of dark matter is termed as ``Cannibalism'' process. In this work, the self-interaction of dark matter and the strength of such interactions are investigated in the light of experimental results of the global 21-cm spectrum of neural hydrogen from the era of cosmic dawn. From the present work, it appears that $2\rightarrow 2$ process is much more dominant over the $3\rightarrow 2$ process. It is also found that such interactions affect the dark matter-baryon elastic scattering cross-section. The study also indicates the presence of multi component dark matter of different mass range in the Universe.