A complete study of the one-loop induced decay $\overrightarrow{Z}\overline{\nu }\nu \gamma$ is presented within the framework of the standard model. The advantages of using a nonlinear gauge are stressed. We have found that the main contributions come from the electric dipole and the magnetic dipole transitions of the Z gauge boson and the neutrino, respectively. We obtain a branching ratio $B\left(\overrightarrow{Z}\overline{\nu }\nu \gamma \right)=7.16\mathrm{}\times {10}^{-10},$ which is about four orders of magnitude smaller than the bound recently obtained by the L3 Collaboration and thus it leaves open a window to search for new physics effects in single-photon decays of the Z boson.

• Received 6 January 1999

DOI:https://doi.org/10.1103/PhysRevD.60.013004