Unobstructedness of deformations of holomorphic maps onto Fano manifolds of Picard number 1

TL;DR

This paper proves that deformations of surjective morphisms onto certain Fano manifolds with Picard number 1 are unobstructed and rigid, under conditions related to their minimal rational tangents, covering most known cases.

Contribution

It establishes unobstructedness and rigidity of deformations for morphisms onto Fano manifolds of Picard number 1 under new conditions involving minimal rational tangents.

Findings

Deformations are unobstructed and rigid modulo automorphisms.

Conditions hold for almost all known Fano manifolds of Picard number 1.

Proof techniques vary based on the nature of the variety of minimal rational tangents.

Abstract

We show that deformations of a surjective morphism onto a Fano manifold of Picard number 1 are unobstructed and rigid modulo the automorphisms of the target, if the variety of minimal rational tangents of the Fano manifold is non-linear or finite. The condition on the variety of minimal rational tangents holds for practically all known examples of Fano manifolds of Picard number 1, except the projective space. When the variety of minimal rational tangents is non-linear, the proof is based on an earlier result of N. Mok and the author on the birationality of the tangent map. When the varieties of minimal rational tangents of the Fano manifold is finite, the key idea is to factorize the given surjective morphism, after some transformation, through a universal morphism associated to the minimal rational curves.