Phenomenology of the notion of an unparticle $\mathcal{U}$, recently perceived by Georgi, to describe a scale invariant sector with a nontrivial infrared fixed point at a higher energy scale is explored in details. Behaving like a collection of $d_{\mathcal{U}}$ (the scale dimension of the unparticle operator ${\mathcal{O}}_{\mathcal{U}}$) invisible massless particles, this unparticle can be unveiled by measurements of various energy distributions for the processes $Z\to f\overline{f}\mathcal{U}$ and $e^{-}{e}^{+}\to \gamma \mathcal{U}$ at $e^{-}{e}^{+}$ colliders, as well as monojet production at hadron colliders. We also study the propagator effects of the unparticle through the Drell-Yan tree-level process and the one-loop muon anomaly.

• Received 19 April 2007

DOI:https://doi.org/10.1103/PhysRevLett.99.051803