Unparticle physics

I only stumbled across Howard Georgi's latest work when his paper "Another odd thing about unparticle physics" appeared on the Arxiv today. Clearly there was a first odd thing to know about unparticle physics, which leads the reader to "Unparticle physics". This is a very short paper with some fascinating commentary on a possible, previously unremarked scenario for LHC phenomenology (unremarked as far as I'm aware).

The idea is to have a non-trivial scale invariant sector, at least with an IR fixed point, and see how the coupling between the normal particle sector and the scale invariant sector, using effective field theory techniques, effects the low energy physics. The strange terminology is used because in a scale invariant theory the quantum mechanical treatment of particles doesn't make sense and Georgi names the 'stuff' 'unparticles'. The question he tackles in the first paper is what signals one would see in the accelerator if there is a coupling between unparticles and particles. The answer is that although the theory may be highly non-linear, the conformal nature means that the correlation functions can be understood simply through the scaling behavior of the unparticle operators.

Depending on the scaling dimension of the 'stuff' the signature gives a different decay width of regular particles as a function of energy. This very specific signature would be quite clear, giving signals of missing energy at particle accelerators, in a different form from SUSY or large extra dimensions.

The paper is short and clear and gives a hint that there's lots of interesting, easy phenomenology to extract from this strange but not necessarily crazy model. Two new papers today follow this although in the conclusions of the latter paper it seems that the signals from the LHC would not be so clear.