The effect of pion mass on Skyrme configurations
  In the Skyrme model, atomic nuclei are identified with solitonic configurations. If the pion mass is set to zero, these configurations are spherical shells of energy with a fullerene-like appearance and are well approximated by a simple rational map ansatz. Using simulated annealing, we have calculated minimum energy configurations for non-zero pion mass and have found that they are less round and are less well approximated by the rational map ansatz. 
Conor Houghton and Shane Magee