K->pipie+e- decays and chiral low-energy constants

The branching ratios of the measured decay $K_L\to\pi^+\pi^-e^+e^-$ and of the still unmeasured decay $K^+\to\pi^+\pi^0e^+e^-$ are calculated to next-to-leading order in Chiral Perturbation Theory (CHPT). Recent experimental results are used to determine two possible values of the combination $(N^r_{16}-N_{17})$ of weak low-energy couplings (LECs) from the $\mathcal{O}(p^4)$ chiral Lagrangian. The obtained values are compared to the predictions of theoretical approaches to weak counterterm couplings to distinguish between the two values. Using the favoured value of the combination $(N^r_{16}-N_{17})$ and taking into account additional assumptions suggested by the considered models, one obtains the branching ratio of the second decay as a function of the unknown combination $(N^r_{14}+2N^r_{15})$ of weak low-energy couplings. Finally, using values of the individual LECs derived from a particular model, one predicts the branching ratio of the $K^+$ decay.Comment: 38 pages, 6 figures. Slightly enlarged version, references added, results unchanged. Accepted for publication in Eur.Phys.J.

The pionic beta decay in chiral perturbation theory

Within the framework of chiral perturbation theory with virtual photons and leptons, we present an updated analysis of the pionic beta decay including all electromagnetic contributions of order e**2 p**2. We discuss the extraction of the Cabibbo-Kobayashi-Maskawa matrix element |Vud| from experimental data. The method employed here is consistent with the analogous treatment of the Kl3 decays and the determination of |Vus|.Comment: 8 pages, 1 figure, latex file, uses EPJC macro

The CP-violating asymmetry in K_L -> pi+ pi- e+ e-

We update the theoretical analysis of the CP-violating asymmetry in the decay K_L -> pi+ pi- e+ e-, relying on chiral perturbation theory and on the most recent phenomenological information. With the experimentally determined magnetic amplitude and branching ratio as input, the asymmetry can be calculated with good accuracy. The theoretical interpretation of the sign of the asymmetry is discussed.Comment: 11 page