http://arxiv.org/abs/1809.00177
The stronger than expected 21-cm absorption was observed recently, and another anomaly of $^8$Be transitions would be signatures of new interactions. The two issues may be related to each other, e.g., pseudoscalar $A$ mediated fermionic millicharged DM, and the 21-cm absorption could be induced by the scattering between MeV millicharged DM and hydrogen. This will be explored in this paper. For fermionic millicharged DM $\bar{\chi} \chi$ with masses in a range of $2 m_A < 2 m_{\chi} < 3 m_A$, the p-wave annihilation $\bar{\chi} \chi \to A A$ would be dominant during DM freeze-out. The s-wave annihilation $\bar{\chi} \chi$ $\to A, \gamma $ $\to e^+ e^-$ is below the constraints from CMB and the 21-cm absorption. The millicharged DM of concern can evade constraints from direct detection experiments. The process of $K^+ \to \pi^+ \pi^0$ with the invisible decay $\pi^0 \to \bar{\chi} \chi$ could be employed to search for the millicharged DM, and future high intensity $K^+$ sources, such as NA62, will do the job.
L. Jia, X. Deng and C. Liu
Wed, 5 Sep 18
63/133
Comments: 5 pages, 2 figures
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