Comments on the Unitarity Bound inKL0→μ+μ−

Abstract

Two alternatives to reconcile the present disagreement between experiment and the "simple" unitarity bound in $K_L^0\to {\mu }^{+}{\mu }^{-}$ are considered. These alternatives presume that $\mathrm{CP}$ violation does not play the dominant role (via $\mathrm{Re}\epsilon$) in the resolution of this puzzle. They are (1) the introduction of new muonic interactions, and (2) the existence of a new pseudoscalar meson. The first alternative can already be eliminated by present experimental evidence. The second alternative must satisfy a number of restrictions.