Constraints on RadiativeZ0Decays

We study an effective local interaction as a possible source of hard photons in the decay $Z_0\to \overline{\mathrm{ll}}\gamma$. We restrict the form of this interaction by the requirements that it be SU(2) ⊗ U(1) gauge invariant, $\mathrm{CP}$ invariant, and chirality conserving. Including constraints derived from the agreement of the standard model in other neutral current experiments, we find that the ratio of radiative to nonradiative leptonic decay widths is given by $0.6{\left(\frac{M_Z}{M_{\Lambda }}\right)}^4$ where $M_{\Lambda }$ is the mass scale characterizing the "new physics." This ratio is less than the preliminary experimental indication of approximately 10% if $M_{\Lambda }$ is greater than 150 GeV.