Nonrelativistic pion interactions and the pionium lifetime - art. no. 014031.

We construct an effective Lagrangian for interacting pions with non-relativ istic energies. The coupling constants can be expressed in terms of the dif ferent scattering lengths and slopes. When used in the calculation of the p ionium decay rate, the scattering slope contribution gives a correction of about 8% compared with the lowest order contribution coming from the scatte ring lengths alone. [S0556-2821(98)07623-1].