Dark matter models for the 511 keV galactic line predict keV electron recoils on Earth Yohei Ema, Filippo Sala and Ryosuke Sato Eur. Phys. J. C, 81 2 (2021) 129 Published online: 06 February 2021 DOI: 10.1140/epjc/s10052-021-08899-y