CP Conserving and Violating Contributions to   $K_L\to\pi^+\pi^-\nu\bar{\nu}$
  We study both CP conserving and violating contributions to the decay $K_L\to\pi^+\pi^-\nu\bar{\nu}$. We find that the decay branching ratio is dominated by the CP conserving part. In the standard CKM model, we estimate that for $m_t\sim 174\ GeV$, the branching ratio due to the CP conserving (violating) contributions can be as large as $4.4 \times 10^{-13}$ ($1.0\times 10^{-14}$). 
C.Q. Geng, I.J. Hsu and Y.C. Lin