Rectifiability and upper Minkowski bounds for singularities of harmonic   Q-valued maps
  In this article we prove that the singular set of Dirichlet-minimizing $Q$-valued functions is countably $(m-2)$-rectifiable and we give upper bounds for the $(m-2)$-dimensional Minkowski content of the set of singular points with multiplicity $Q$. 
Camillo de Lellis, Andrea Marchese, Emanuele Spadaro and Daniele   Valtorta
math.AP