Nonresonant three-body decays of charmed mesons.

Nonresonant three-body decays of charmed mesons are first studied in the approach of effective SU(4){times}SU(4) chiral Lagrangians. It is pointed out that the predictions of the branching ratios in chiral perturbation theory are in general too small when compared with experiment. However, the experimental results are comprehensible in the general framework of the quark-diagram scheme. The existence of a sizable {ital W}-annihilation amplitude, which is evident by the observation of {ital D}{sub {ital s}}{sup +}{r arrow}({pi}{sup +}{pi}{sup +}{pi}{sup {minus}}){sub NR}, is the key toward an understanding of the three-body nonresonant decays of {ital D}{sup +} and {ital D}{sub {ital s}}{sup +}. The measurement of {ital D}{sup 0}{r arrow}{bar K} {sup 0}K{sup +}K{sup {minus}} and {ital D}{sup 0}{r arrow}{bar K}{sup 0}{pi}{sup +}{pi}{sup {minus}} indicates that color suppression is not effective in the three-body decay. Based on the quark-diagram analysis, predictions for some other nonresonant modes are given.