On the Futaki invariant of Fano threefolds

TL;DR

This paper investigates the Futaki invariant on K-polystable Fano threefolds, showing it vanishes on most cases and constructing families of Kähler classes with zero Futaki invariant, implying existence of non-Kähler-Einstein cscK metrics.

Contribution

It characterizes the zero locus of the Futaki invariant on Fano threefolds and constructs explicit families of Kähler classes with zero Futaki invariant, revealing new geometric structures.

Findings

Futaki invariant vanishes on most Fano threefolds except specific families.

Explicit 2-dimensional families of Kähler classes with zero Futaki invariant are constructed.

Non Kähler-Einstein cscK metrics exist on these Fano threefolds.

Abstract

We study the zero locus of the Futaki invariant on K-polystable Fano threefolds, seen as a map from the K\"ahler cone to the dual of the Lie algebra of the reduced automorphism group. We show that, apart from families 3.9, 3.13, 3.19, 3.20, 4.2, 4.4, 4.7 and 5.3 of the Iskovskikh-Mori-Mukai classification of Fano threefolds, the Futaki invariant of such manifolds vanishes identically on their K\"ahler cone. In all cases, when the Picard rank is greater or equal to two, we exhibit explicit 2-dimensional differentiable families of K\"ahler classes containing the anti-canonical class and on which the Futaki invariant is identically zero. As a corollary, we deduce the existence of non K\"ahler-Einstein cscK metrics on all such Fano threefolds.