Let M be a compact complex manifold acted on by a compact Lie group G. Let L → M be a G-equivariant holomorphic line bundle that is assumed to be ample. Note that the G-action on L → M extends to the complex reductive group G C [9].In this context, we are interested in the family of G-modules Γ(M, L ⊗n ) formed by the holomorphic sections, and more particularly to the sequence H(n) := dim Γ(M, L ⊗n ) G , n ≥ 1. For any holomorphic G-complex vector bundle E → M , we consider also the sequenceOur main result, that we will detail in the next Section, can be summarized as follows : if the sequence H(n) is bounded, then the sequence H E (n) is bounded for any holomorphic G-complex vector bundle E and we can compute its value for large n.
Stability resultSince the line bundle L is ample, there exists an Hermitian metric h on L such that the curvature Ω := i(∇ h ) 2 of its Chern connection ∇ h is a Kähler class : Ω is a symplectic form on M that is compatible with the complex structure. By an averaging process we can assume that the Gaction leaves the metric and connection invariant. Hence we have a moment map Φ : M → g * defined by Kostant's relationsHere L(X) is the Lie derivative on the sections of L, and X M (m) := d ds e −sX · m| s=0 is the vector field generated by X ∈ g.The [Q, R] = 0 Theorem of Meinrenken [16] and Meinrenken-Sjamaar [17] says that the moment map Φ gives a geometric interpretation of the sequence H(n). An important object here is the reduced space M 0 := Φ −1 (0)/G which is homeomorphic to the Mumford GIT quotient M/ /G C [11].