Also, my same analysis based in Salamin's simple calculation, also would indicate (if you believe that paper's 0.1 cm^2 / gram claim) that Dark Matter cannot interact via EM force (would then not be "dark") or gravity, weak force, or strong force, or Higgs force (too small cross section since the latter 3 forces too short ranged, and gravity too weak). In short, dark matter cannot be a particle at all subject to any of the forces were are aware of, it must be subject to some new force we have never yet found. Specifically, the length scales for the forces are: weak: r=10^(-17) meter, arising from masses of W and Z bosons m=80-92 GeV/c^2 hence r=hbar/(m*c)=2.47*10^(-18) meter is the factor-e-falloff length for Yukawa potential. higgs: similar but a little shorter range, using mass of Higgs boson 126 GeV/c^2. strong: the "residual strong force" using pions as a force carrier has range 1-3 fm (but using gluons is shorter ranged). Anyhow, strong is the crux. If the dark matter particles have mass=300*ProtonMass, which seems the smallest one could possibly hope for, then with a cross section of pi*(3fm)^2 = 2.8*10^(-29) meter^2 = 2.8*10^(-25) cm^2 per particle, that is for a gram of particles a cross section of 5.7*10^(-4) cm^2. This is way smaller than the minimum the paper claims is allowed by observation, namely 0.1 cm^2. So we conclude either the paper's 0.1 claim is garbage, or dark matter cannot exist as particles, or a new force is involved. That awesome News Source, the "Daily Mail" appears to have somewhat figured this out(!): http://www.dailymail.co.uk/sciencetech/article-3013284/Is-dark-matter-FLUID-...