Pico-charged intermediate particles rescue dark matter interpretation of 511 keV signal

Abstract

Various alleged indirect dark matter search signals, such as the 511 keV line from galaxy center or the PAMELA/AMS02 signal, are often challenged by the absence of corresponding signal from dwarf galaxies and/or from the absence of an impact on CMB through delayed recombination. We propose a novel scenario that can avoid these bounds based on the decay of dark matter, X, to a pair of intermediate particles C and \bar{C} with a lifetime much greater than the age of universe. The annihilation of these intermediate particles eventually leads to a dark matter signal. The bounds from CMB can be easily avoided by the fact that at the time of recombination, not enough C particles had been accumulated. In order to keep C particles from leaving the galaxy, we assume the particles have a small electric charge so in the galactic disk, the magnetic field keeps the C particles in the vicinity of their production. However, they can escape the dwarf galaxies and the dark matter halo where the magnetic field is weak, leading to null signal from these regions. The small charge can have interesting consequences including a signal in direct dark matter searches.