2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/114129The Donagi-Markman cubic is the differential of the period map for algebraic completely integrable systems. Here we prove a formula for the cubic in the case of Hitchin's system for arbitrary $\mathfrak g$. This was originally stated (without proof) by Pantev for ${\mathfrak sl}_n$.Final version, minor changes made at request of refereeAlgebraic GeometrySymplectic Geometrytext