Just when I’m finally starting to get a bit of a handle on what’s going on in particle physics (or at least map out the areas of my ignorance), along comes Howard Georgi with “Unparticle Physics”:
I discuss some simple aspects of the low-energy physics of a nontrivial scale invariant sector of an effective field theory–physics that cannot be described in terms of particles. I argue that it is important to take seriously the possibility that the unparticle stuff described by such a theory might actually exist in our world. I suggest a scenario in which some details of the production of unparticle stuff can be calculated. I find that in the appropriate low-energy limit, unparticle stuff with scale dimension d[script U] looks like a nonintegral number d[script U] of invisible particles. Thus dramatic evidence for a nontrivial scale invariant sector could show up experimentally in missing energy distributions.
Were it anywhere other than Physical Review Letters, I would suspect that this was a put-on, just to mess with low-energy experimentalists. It’s an editor’s recommendation at PRL, though, so if it is a gag, it goes all the way to the top of the profession.
I’m aware that this thing has been on the ArXiV for months, and has generated a number of papers in response. Which hopefully means that somebody out there understands what it’s about, and can explain it to me as if I were a rather stupid child of four, because I’ve got nothing, here.