Analysis of $K_L \to \gamma \nu \bar{\nu}$

Abstract

The decay $K_L \to \gamma \nu \bar{\nu}$ is analyzed within the standard model. Short-distance contributions are found to dominate, yielding a branching ratio of $\sim 0.7 \times 10^{-11}$. We examine the possibility that non-standard model effects might be observed at higher rates. As an example, we calculate the branching ratio for the process mediated by neutral horizontal gauge bosons. Notwithstanding some model uncertainties, experimental limits for lepton number violation constrains these contributions to $\lesssim 2\times 10^{-11}$.