Tests of Dark MACHOs: Lensing, Accretion, and Glow

Abstract: Dark matter could take the form of dark massive compact halo objects (dMACHOs); i.e., composite objects that are made up of dark-sector elementary particles, that could have a macroscopic mass from the Planck scale to above the solar mass scale, and that also admit a wide range of energy densities and sizes. Concentrating on the gravitational interaction of dMACHOs with visible matter, we map out the mass-radius parameter space that is consistent with gravitational lensing experiments, as well as anisotropies of the cosmic microwave background (CMB) based on the spherical accretion of matter onto a dMACHO in the hydrostatic approximation. For dMACHOs with a uniform-density mass profile and total mass in the range of $\sim 10^{-12} - 10\,M_\odot$, we find that a dMACHO could explain 100% of the dark matter if its radius is above $\approx 3$ times the Einstein radius of the lensing system. For a larger mass above $10\,M_\odot$, a dMACHO with radius above $\sim 1 \times 10^8 \mbox{cm} \times(M/100\,M_\odot)^{9/2}$ is consistent with CMB observables. For a lighter dMACHO with mass below $\sim 10^{-12}\,M_\odot$, there still is not a good experimental probe. Finally, we point out that heavier dMACHOs with masses $\sim 0.1\,M_\odot$ may be observed by X-ray and optical telescopes if they reside at rest in a large molecular cloud, nearby to our solar system, and accrete ordinary matter to emit photons.