Unparticle Physics

I discuss some simple aspects of the low-energy physics of a nontrivial scaleinvariant sector of an effective field theory -- physics that cannot bedescribed in terms of particles. I argue that it is important to take seriouslythe possibility that the unparticle stuff described by such a theory mightactually exist in our world. I suggest a scenario in which some details of theproduction of unparticle stuff can be calculated. I find that in theappropriate low energy limit, unparticle stuff with scale dimension$d_{\mathcal{U}}$ looks like a non-integral number $d_{\mathcal{U}}$ ofinvisible particles. Thus dramatic evidence for a nontrivial scale invariantsector could show up experimentally in missing energy distributions.Comment: 9 pages, 1 figure - more references and minor wording changes in v