Equivariant calculus on $\mu$-character and $\mu$K-stability of polarized schemes

Abstract

We introduce and study $\mu$K-stability of polarized schemes with respect to general test configurations as an algebro-geometric aspect of the existence of $\mu$-cscK metrics, which is introduced in the paper arXiv:1902.00664 as a framework unifying the frameworks of K\"ahler-Ricci solitons and cscK metrics. This article consists of two ingredients. On one hand, we develop a foundational framework concerning `derivative of relative equivariant intersection', which we call equivariant calculus. A core claim in equivariant calculus is a convergence result for some infinite series in equivariant cohomology, which is obtained by relative equivariant intersections. Our proof is based on some observations on deRham-Cartan model of equivariant locally finite homology. This framework furnishes a language to describe $\mu$K-stability. We in particular conclude the $\mu$K-semistability of $\mu$-cscK manifolds with respect to general test configurations. On the other hand, we introduce an equivariant character $\mathbf{\check{\mu}}^\lambda$ called $\mu$-character for equivariant family of polarized schemes, motivated by the $\mu$-volume functional introduced in the paper arXiv1902.00664 as a generalization of Tian-Zhu's functional in the theory of K\"ahler-Ricci soliton. The equivariant derivative of the $\mu$-character derive $\mu$-Futaki invariant for general test configuration, and furthermore, it also produces an analogue of the equivariant first Chern class of CM line bundle for family of polarized schemes, which is irrational and hence cannot be realized as a $\mathbb{Q}$-line bundle in our general $\mu$K-stability setup.