Abstract. We show that for any polarized compact Kähler manifold, the extremal Kähler metrics that represent the given cohomology class can be characterized as critical points of a suitably defined K-energy functional.
Let (M,JHere s ω and dµ ω are the scalar curvature and volume form of ω, respectively. Calabi computed the Euler-Lagrange equation, and showed that the critical metrics of this functional are those for which the gradient of the scalar curvature is a realholomorphic vector field. He called these metrics extremal.Inspired by the work of Donaldson on Yang-Mills connections on stable bundles, Mabuchi [7] introduced the K-energy functional on Ω + for polarized manifolds with positive first Chern class. The critical points of this functional are Kähler Einstein metrics, and it has played a significant role in the study of these metrics for this type of manifolds [1,4]. The purpose of this note is to show that extremal Kähler metrics can also be defined as critical points of a functional analogous to the K-energy.Let G be a maximal compact subgroup of the biholomorphism group of (M, J), and let g be a Kähler metric on M with Kähler class Ω. Without loss of generality, we assume that g is G-invariant. We denote by L 2 k,G the real Hilbert space of Ginvariant real-valued functions of class L 2 k , and consider G-invariant deformations of this metric preserving the Kähler class:In this expression, the condition k > n ensures that L 2 k,G is a Banach algebra, making the scalar curvature ofω a well-defined function in the space.