Exact topological density in the lattice Skyrme model
  We propose using the Skyrme model on a lattice as an effective field theory of meson-baryon interactions. To this end we construct a local topological density that involves the volumes of tetrahedra in the target space S^3 and we make use of Coxeter's formula for the Schlafli function to implement it. We calculate the mean-square radius of a skyrmion in the three-dimensional Skyrme model, and find some surprises. 
Benjamin Svetitsky and Alec Schramm