Bounds on Dark Matter Annihilation Cross-sections from Inert Doublet Model in the context of 21 cm Cosmology of Dark Ages

We study the fluctuations in the brightness temperature of 21-cm signal $\delta T_{21}$ at the dark ages ($z\sim100$) with a dark matter candidate in Inter Doublet Model (IDM). We then explore the effects of different fractions of IDM dark matter on $\delta T_{21}$ signal. The IDM dark matter masses are chosen in few tens of GeV region as well as in the high mass region beyond 500 GeV. It has been observed that the $\delta T_{21}$ signal is more sensitive in the dark matter mass range of $70 - 80$ GeV. A lower bound on annihilation cross-section for this dark matter is also obtained analyzing the $\delta T_{21}$ signal. This is found to lie within the range $6.5 \times 10^{-29} \,\, \rm{cm^3 / sec} \leq \langle\sigma v\rangle \leq 4.88\times 10^{-26}\,\, \rm{cm^ 3 / sec}$ for the IDM dark matter mass range $10 \, {\rm GeV} \leq m_{\chi}\leq 990 \,{\rm GeV} $.