The most recent attempt in this direction is Georgi´s proposal of ”unparticles” which are thought to lead to an ”invisibility” of a certain kind of outgoing matter component, which shows its presence through the appearance of energy-momentum-carrying but otherwise undetectable ”fractional particle stuff”. Unlike the infraparticle concept this so formulated ”unparticle”-problem is not imposed by any observational fact; it is at this stage a mere mind game, although dark matter is sometimes mentioned as a potential observational application. Clearly what is called ”stuff” by those authors is outside the standard particle world and its conjectured appearance together with scattering of ordinary particles is part of the larger ”asymptotic completeness” problem i.e. of the question whether it is possible that the particles which emerge asymptotically in a scattering process do not form a complete set of states but leave some stuff which dissipated into the vacuum in such a way that it cannot be accounted for in particle registering devices. So any set of physical assumption which leads to asymptotic completeness has a bearing on this problem; we will return to this point at the end of the paper.https://arxiv.org/pdf/0804.3563.pdf
Unparticles are a proposed solution for the dark matter problem.