The decays K->pi pi nu(nu)over-bar within the standard model

We study the reactions K --> <pi pi nu(nu)over bar> within the minimal standard model. We use isospin symmetry to relate the matrix elements to the form factors measured in K-l4. We argue that these modes are short distance dominated and can be used for precise determinations of the CKM parameters rho and eta. Depending on the value of the CKM angles we find branching ratios in the following ranges: B(K-L --> pi(+)pi(+)<nu(nu)over bar>) = [2-5] x 10(-13) B(K-L --> pi(0) pi(0)<nu(nu)over bar>) = [1-3] x 10(-13); B(K+ --> pi(+)pi(0)<nu(nu)over bar>) = [1-2] x 10(-14). We also discuss a possible CP-odd observable.