Boundary height fields in the Abelian sandpile model
  We study the abelian sandpile model on the upper half plane, and reconsider the correlations of the four height variables lying on the boundary. For more convenience, we carry out the analysis in the dissipative (massive) extension of the model and identify the boundary scaling fields corresponding to the four heights. We find that they all can be accounted for by the massive pertubation of a c=-2 logarithmic conformal field theory. 
Geoffroy Piroux and Philippe Ruelle