On the Infinitesimal Torelli theorem for regular surfaces with very ample canonical divisor

Abstract: Let $X$ be a smooth compact complex surface subject to the following conditions: (i) the canonical line bundle $\mathcal{O}_X(K_X) $ is very ample, (ii) the irregularity $q(X): = h^1(\mathcal{O}_X) =0$, (iii) $X$ contains no rational normal curves of degree $\leq (p_g-1)$, (iv) the multiplication map $m_2: Sym^2(H^0(\mathcal{O}_X(K_X))) \longrightarrow H^0 (\mathcal{O}_X (2K_X))$ is surjective. It is shown that the Infinitesimal Torelli holds for such $X$. Our proof is based on the study of the cup-product $$ H^1 (\Theta_X) \longrightarrow (\mathcal{O}_X(K_X))^{\ast} \otimes H^1 (\Omega_X) $$ where $\Theta_X$ (resp. $\Omega_X$) is the holomorphic tangent (resp. cotangent) bundle of $X$. Conceptually, the approach consists of lifting the data of the cohomological cup-product above to the category of complexes of coherent sheaves of $X$. This establishes connections between the geometry of the canonical map and the above cup-product by exhibiting geometrically meaningful objects in the category of (short) exact complexes of coherent sheaves on $X$.