Kähler metrics with constant weighted scalar curvature and weighted K-stability

Abstract

We introduce a notion of a Kähler metric with constant weighted scalar curvature on a compact Kähler manifold $X$, depending on a fixed real torus $\mathbb{T}$ in the reduced group of automorphisms of $X$, and two smooth (weight) functions $\mathrm{v}>0$ and $\mathrm{w}$, defined on the momentum image (with respect to a given Kähler class $\alpha$ on $X$) of $X$ in the dual Lie algebra of $\mathbb{T}$. A number of natural problems in Kähler geometry, such as the existence of extremal Kähler metrics and conformally Kähler, Einstein--Maxwell metrics, or prescribing the scalar curvature on a compact toric manifold reduce to the search of Kähler metrics with constant weighted scalar curvature in a given Kähler class $\alpha$, for special choices of the weight functions $\mathrm{v}$ and $\mathrm{w}$. We show that a number of known results obstructing the existence of constant scalar curvature Kähler (cscK) metrics can be extended to the weighted setting. In particular, we introduce a functional ${\mathcal{M}}_{\mathrm{v},\mathrm{w}}$ on the space of $\mathbb{T}$-invariant Kähler metrics in $\alpha$, extending the Mabuchi energy in the cscK case, and show (following the arguments of Li and Sano--Tipler in the cscK and extremal cases) that if $\alpha$ is Hodge, then constant weighted scalar curvature metrics in $\alpha$ are minima of ${\mathcal{M}}_{\mathrm{v},\mathrm{w}}$. Motivated by the recent work of Dervan--Ross and Dyrefelt in the cscK and extremal cases, we define a $(\mathrm{v},\mathrm{w})$-weighted Futaki invariant of a $\mathbb{T}$-compatible smooth Kähler test configuration associated to $(X,\alpha ,\mathbb{T})$, and show that the boundedness from below of the $(\mathrm{v},\mathrm{w})$-weighted Mabuchi functional ${\mathcal{M}}_{\mathrm{v},\mathrm{w}}$ implies a suitable notion of a $(\mathrm{v},\mathrm{w})$-weighted K-semistability.

A link with Kähler Ricci solitons and the work of E. Inoue arXiv:1802.08128 added. Presentation improved