Explanation of the 511 keV line: cascade annihilating dark matter with the $$^8$$ 8 Be anomaly

• Main Author: Lian-Bao Jia
• Format: Article
• Language: English
• Published: SpringerOpen 2018-02-01
• Series: European Physical Journal C: Particles and Fields
• Online Access: http://link.springer.com/article/10.1140/epjc/s10052-018-5555-0

Abstract A possible dark matter (DM) explanation about the long-standing issue of the Galactic 511 keV line is explored in this paper. For DM cascade annihilations of concern, a DM pair $$\pi _d^{+} \pi _d^{-}$$ πd+πd- annihilates into unstable $$\pi _d^{0} \pi _d^{0}$$ πd0πd0 , and $$\pi _d^{0}$$ πd0 decays into $$e^+ e^-$$ e+e- with new interactions suggested by the $$^8$$ 8 Be anomaly. Considering the constraints from the effective neutrino number $$N_{\mathrm {eff}}$$ Neff and the 511 keV gamma-ray emission, a range of DM is obtained, $$11.6 \lesssim m_{\pi _d^{\pm }} \lesssim 15$$ 11.6≲mπd±≲15 MeV. The typical DM annihilation cross section today is about 3.3 $$\times $$ × $$10^{-29}$$ 10-29 cm$$^3$$ 3 s$$^{-1}$$ -1 , which can give an explanation about the 511 keV line. The MeV scale DM may be searched by the DM-electron scattering, and the upper limit set by the CMB s-wave annihilation is derived in DM direct detections.