On the Harder-Narasimhan filtration for finite dimensional   representations of quivers
  We prove that the Harder-Narasimhan filtration for an unstable finite dimensional representation of a finite quiver coincides with the filtration associated to the 1-parameter subgroup of Kempf, which gives maximal unstability in the sense of Geometric Invariant Theory for the corresponding point in the parameter space where these objects are parametrized in the construction of the moduli space. 
Alfonso Zamora
math.AG math.RT