Small codimension components of the Hodge locus containing the Fermat variety

Abstract

We characterize the smallest codimension components of the Hodge locus of smooth degree $d$ hypersurfaces of the projective space ${\mathbb{P}}^{n+1}$ of even dimension $n$, passing through the Fermat variety (with $d\ne 3,4,6$). They correspond to the locus of hypersurfaces containing a linear algebraic cycle of dimension $\frac{n}{2}$. Furthermore, we prove that among all the local Hodge loci associated to a non-linear cycle passing through Fermat, the ones associated to a complete intersection cycle of type $(1,1,\dots ,1,2)$ attain the minimal possible codimension of their Zariski tangent spaces. This answers a conjecture of Movasati, and generalizes a result of Voisin about the first gap between the codimension of the components of the Noether-Lefschetz locus to arbitrary dimension, provided that they contain the Fermat variety.

Final version, to appear in CCM

References in corpus (2)

• Periods of Complete Intersection Algebraic Cycles
• Integral Hodge conjecture for Fermat varieties

Cited by in corpus (1)

• On fake linear cycles inside Fermat varieties