Non-Relativistic Pion Interactions and the Pionium Lifetime
  We construct an effective Lagrangian for interacting pions with non-relativistic energies. The coupling constants can be expressed in terms of the different scattering lengths and slopes. When used in the calculation of the pionium decay rate, the scattering slope contribution gives a correction of about 8% compared with the lowest order contribution coming from the scattering lengths alone. 
Xinwei Kong, Finn Ravndal (University of Oslo)