  Low energy phenomenology of the unparticle physics associated with an exact
scale invariant sector possessing a non-trivial infrared fixed point at a
higher energy scale is explored for both electron-positron and hadronic
colliders. Feynman rules for a spin 0, 1 or 2 unparticle coupled to a variety
of standard model gauge invariant operators that are relevant to many low
energy processes involving either real emissions of unparticles or their
virtual propagator effects are presented. Missing energy and/or recoil mass
distributions of the unparticle in the associated production of unparticle
together with a photon or $Z$ boson at LEP2 and ILC as well as in $Z$ decay
into an unparticle plus a fermion-antifermion pair are studied. Monojet
production at hadronic collisions is explored. The complex phase in the
unparticle propagator that can give rise to interesting interference effects
between an unparticle exchange diagram and the standard model amplitudes are
studied in details for the Drell-Yan process as well as muon pair and diphoton
production in electron-positron annihilation. These energy and/or recoil mass
distributions (with the exception in hadron colliders) and interference effects
are found sensitively depending not only on the scale dimension but also on the
spin of the unparticle. For the spin-2 unparticle, its physical effects is
found to resemble that of a tower of Kaluza-Klein gravitons, which strongly
indicates that the underlying unparticle physics may have root in a higher
dimensional theory. A connection between unparticle physics and theories of
large extra dimension is speculated. Experimental constraints on the unparticle
scale are deduced from the LEP2 data on mono-photon production and from the
4-fermion contact interactions.
