Difficulties for Compact Composite Object Dark Matter
  It has been suggested ``that DM particles are strongly interacting composite macroscopically large objects ... made of well known light quarks (or ... antiquarks)." In doing so it is argued that these compact composite objects (CCOs) are ``natural explanations of many observed data, such as [the] 511 keV line from the bulge of our galaxy" observed by INTEGRAL and the excess of diffuse gamma-rays in the 1-20 MeV band observed by COMPTEL. Here we argue that the atmospheres of positrons that surround CCOs composed of di-antiquark pairs in the favoured Colour-Flavour-Locked superconducting state are sufficiently dense as to stringently limit the penetration of interstellar electrons incident upon them, resulting in an extreme suppression of previously estimated rates of positronium, and hence the flux of 511 keV photons resulting from their decays, and also in the rate of direct electron-positron annihilations, which yield the MeV photons proposed to explain the 1-20 MeV excess. We also demonstrate that even if a fraction of positrons somehow penetrated to the surface of the CCOs, the extremely strong electric fields generated from the bulk antiquark matter would result in the destruction of positronium atoms long before they decay. 
Daniel T. Cumberbatch, Glenn D. Starkman and Joseph Silk