The infinitesimal Torelli problem

Abstract

Let $g \geq 2$ and let the Torelli map denote the map sending a genus $g$ curve to its principally polarized Jacobian. We verify the well known fact that the map induced on tangent spaces by the Torelli map is dual to the multiplication map $\mathrm{Sym}^2 H^0(C, \omega_C) \rightarrow H^0(C, \omega_C^{\otimes 2})$.