Credit: Alan Stonebraker

Figure 1: (Top) $K→πνν¯$ decays are mediated by the flavor-changing neutral-current transition $s→dνν¯$ (here $s$ and $d$ stand for strange and down quarks). (Bottom) Representative one-loop diagrams contributing to the $s→dνν¯$ amplitude within the standard model (left) and within an extension of the standard model (right).