Could Dark Matter be partially explained by the somewhat obvious fact that weakly interacting particles are affected by gravity like everything else in the universe, and therefore could coagulate over great periods of time, and may have differing cycles of accretion, and expansion then other types of matter. In an invisible way, these weakly interacting particles pass right by one another, and other matter - much like galaxies that collide, but don't actually collide at first because there is so much space between things - but the galaxies are affected by the gravity of the other - so their relative velocities slow, and they eventually become one. Some of Dark matter could and probably does function in much the same way - it doesn't collide with other particles, but it does affect it's relative mean velocity, and it eventually coalesces into regular / stable "orbits" if you will - maitaining some or most of their origional momentum. Since they experience very little or no interaction, (besides gravity) with other particles, there is no friction of anykind to slow them down - this would have an intesting effect on not only the gravitational capture, but also of how they orbit extreemly dense objects - sometimes passing right through them etc.