Strong rescattering in K-->3 pi decays and low-energy meson dynamics

Direct CP Violation in K→μ^{+}μ^{-}

A rare decay K_{L}→μ^{+}μ^{-} has been measured precisely, while a rare decay K_{S}→μ^{+}μ^{-} will be observed by an upgrade of the LHCb experiment. Although both processes are almost CP-conserving decays, we point out that an interference contribution between K_{L} and K_{S} in the kaon beam emerges from a genuine direct CP violation. It is found that the interference contribution can change K_{S}→μ^{+}μ^{-} standard-model predictions at O(60%). We also stress that an unknown sign of A(K_{L}→γγ) can be determined by a measurement of the interference, which can much reduce a theoretical uncertainty of B(K_{L}→μ^{+}μ^{-}). We also investigate the interference in a new physics model, where the ε_{K}^{'}/ε_{K} tension is explained by an additional Z-penguin contribution.

Determination of the a0-a2 pion scattering length from K+-->pi+pi0pi0 decay

We present a new method for the determination of the pi-pi scattering length combination a(0)-a(2), based on the study of the pi(0)pi(0) spectrum in K+-->pi(0)pi(0)pi(+) in the vicinity of the pi(+)pi(-) threshold. The method requires a minimum of theoretical input, and is potentially very accurate.