A note on Infraparticles and Unparticles
  The observed astrophysical phenomenon of dark matter has generated new interest in the problem of whether the principles underlying QFT are consistent with invisibility/inertness of energy-momentum carrying "stuff" as e.g. "unparticles". We show that the 2-dim. model which has been used to illustrate the meaning of unparticles belongs to the class of former infraparticles models and the latter are known to describe electrically charged particles in d=1+3 which despite their nonlocality are our best particle physics "candles". The "invisibility" in this case refers to the infinite infrared photon cloud with energies below the resolution and can be made arbitrarily small by increasing the photon registering sensitivity. This is not quite the kind of invisibility which the unparticle community attributes to their invisible "stuff" and which would probably contradict the asymptotic completeness property. The main aim of the present work is to show that knowledge about this part of QFT is still in its infancy and express the hope that the work on unparticles may rekindle a new interest in conceptually subtle old unsolved important problems. 
Bert Schroer