A short proof of a conjecture of Matsushita

In this note we build on the arguments of van Geemen and Voisin to prove a conjecture of Matsushita that a Lagrangian fibration of an irreducible hyperkähler manifold is either isotrivial or of maximal variation. We also complete a partial result of Voisin regarding the density of torsion points of sections of Lagrangian fibrations.