Let $M$ be a compact smooth manifold, and $F\subset TM$ a smooth foliation. It is called transversally Kähler if the normal bundle $TM/F$ is equipped with a Hermitian structure (that is, a complex structure and a Hermitian metric) which is locally obtained as a pullback of a Kähler structure on the leaf space. Sasakian manifolds are prime examples of transversally Kähler manifolds (the leaf space of the Reeb foliation on a Sasakian manifolds is Kähler).
A differential form on $M$ is called basic if it vanishes on $F$ and is locally obtained as a pullback of a form on the leaf space. The basic forms are preserved by de Rham differential, and the cohomology of the basic forms is called the basic cohomology.
A foliation is taut if the top basic cohomology is non-zero (this is not the usual definition, but a theorem of Habib and Richardson). For taut foliations, one has also Poincaré duality on the basic cohomology, and the identification between the basic cohomology and the basic harmonic forms if a transversal Riemannian structure is given.
When $F$ is taut and transversally Kähler, the basic cohomology satisfy all the nice properties of the cohomology of the Kähler manifolds: the dd^c-lemma, the Hodge decomposition, the Hodge structure, Lefschetz SL(2)-action and so on. This is a folklore result of sorts, which follows (without much difficulty) from the Habib–Richardson theorem identifying the basic cohomology and basic harmonic forms.
I think I can prove the Calabi–Yau theorem (that is, the uniqueness and existence of the solutuions of the complex Monge–Ampère equation) for the basic forms; the proof is essentially the same as the usual Calabi–Yau, with the only (minor) modification in the $C^0$-estimates. The result is as follows.
THEOREM: Let $V$ be a basic volume form, and $\omega$ a transversal Kähler form on a taut foliated manifold $(M, F)$, with $\operatorname{dim}(M) -\operatorname{rk}(F)=k$. Assume that $\int_{M/F} V = \int_{M/F} \omega^k$, where $\int_{M/F}$ denotes the projection to the top degree basic cohomology class, given by the tautness of $F$. Then there exists a basic function $\phi$ such that $(\omega+dd^c \phi)^k=V$, and $\phi$ is unique up to a constant.
I suspect the result is already known in some other disguise. Could someone please enlighten me if this is known, and what are the good terms I should look in Google for this kind of stuff? From the search it is painfully obvious that "transversally Kähler" is something that only Sasakian people know and use. I suspect some other term is commonly used instead of "transversally Kähler", because the notion is ubiquitous.
K\"ahler
doesn't work here (it renders asK"ahler
). Instead, one must use Unicode directly, like Kähler. I edited accordingly. $\endgroup$