Speaker
Description
Non-thermal dark matter produced via freeze-in is a well-motivated scenario and it can explain the null results of direct detection experiment because of its feeble interaction with the standard model (SM) particles. In this work, we have considered a minimal extension of SM by adding an SM gauge singlet and $\mathbb{Z}_2$ odd Dirac fermion $\chi$ which is the dark matter candidate, a pseudo scalar $\tilde{\phi}$ which also SM gauge singlet but $\mathbb{Z}_2$ even. $\chi$ interacts with the SM fields via dimension five operator and because of that, the couplings are suppressed by a heavy mass scale $\Lambda$. We have studied the production of the DM candidate via UV, IR and mixed freeze-in in detail and found that for $10^{10}\,{\rm GeV}\,\leq\,\Lambda\leq 10^{15}$ GeV, $\chi$ is dominantly produced via UV and mixed UV-IR freeze-in when reheat temperature $T_{\rm RH} \gt 10^4$ GeV and the production is dominated by IR and mixed freeze-in below $T_{\rm RH} \simeq 10^4$ GeV. We have studied the cascade annihilation $\chi \bar{\chi} \rightarrow \tilde{\phi}\tilde{\phi}\rightarrow 4\gamma$ to address the $\sim 3.5$ keV X-ray line observed from various galaxies taking into account the long lifetime of $\tilde{\phi}$. Finally the allowed parameter space for $\Lambda - g$ plane is obtained by comparing the X-ray flux from the Milky-Way galaxy observed by XMM Newton telescope.
