Let (M,ω) be a Kaehler manifold with Kaehler form ω. Does it exist another Kaehler form ω′ in the same cohomology class of ω such that the Ricci form Ric′ of ω′ is harmonic either for ω or for ω′?
ω′∈[ω]
1) harmonic for ω:
ΔωRic′=0
2) harmonic for ω′:
Δω′Ric′=0