A Note on Unparticle Decays

Understand

The coupling of an unparticle operator O_U to Standard Model particles opens up the possibility of unparticle decays into standard model fields.

• We study this issue by analyzing the pole structure (and spectral function) of the unparticle propagator, corrected to account for one-loop polarization effects from virtual SM particles.
• We find that the propagator of a scalar unparticle (of scaling dimension 1 < d_U < 2) with a mass gap m_g develops an isolated pole, m_p^2-i m_p Gamma_p, with m_p^2 < m_g^2 below the unparticle continuum that extends above m_g (showing that the theory would be unstable without a mass gap).
• If that pole lies below the threshold for decay into two standard model particles the pole corresponds to a stable unparticle state (and its width Gamma_p is zero).