Hilbert schemes of K3 surfaces are dense in moduli
  We prove that the locus of Hilbert schemes of n points on a projective K3 surface is dense in the moduli space of irreducible holomorphic symplectic manifolds of that deformation type. The analogous result for generalized Kummer manifolds is proven as well. 
Eyal Markman and Sukhendu Mehrotra
math.AG