Let $X$ be a compact Kähler manifold. The so-called Kodaira problem asks whether $X$ has arbitrarily small deformations to some projective varieties. While Kodaira proved that such deformations always exist for surfaces. Starting from dimension 4, there are examples constructed by Voisin which answer the Kodaira problem in the negative. In this talk, we will focus on threefolds, as well as compact Kähler manifolds of algebraic dimension $a(X) = dim(X) -1$. We will explain our positive solution to the Kodaira problem for these manifolds.[-]

Malgré les succès de la théorie de Hodge non abélienne de Corlette-Simpson pour exclure que de nombreux groupes de présentation finie soient groupes fondamentaux de variétés projectives lisses (ou des groupes Kähleriens), les techniques de construction manquent. La construction de Campana du groupe fondamental orbifold d'une paire orbifolde permet de considérer le groupe fondamental des compactifications orbifolds d'une variété (ou champ) quasiprojective lisse donnée $U$ qui, si quelques précautions sont prises et sous des hypothèses raisonnables - mais pas toujours faciles a vérifier, est un groupe Kählerien. En choisissant bien la variété $U$, les groupes obtenus sont potentiellement intéressants et on utilise souvent des techniques inattendues pour établir les propriétés de leurs représentations linéaires. L'exposé fera un survey de cas particulièrement intrigants ou, par exemple, $U$ est un complément d'arrangement de droites, une variété localement complexe hyperbolique non compacte ou un espace de modules de courbes pointées.[-]

Since the proof of the Calabi conjecture given by Yau, complex Monge-Ampère equations on compact Kähler manifolds have been intensively studied.
In this talk we consider complex Monge-Ampère equations with prescribed singularities. More precisely, we fix a potential and we show existence and uniqueness of solutions of complex Monge-Ampère equations which have the same singularity type of the model potential we chose. This result can be interpreted as a generalisation of Yau's theorem (in this case the model potential is smooth).
As a corollary we obtain the existence of singular Kähler-Einstein metrics with prescribed singularities on general type and Calabi-Yau manifolds.
This is a joint work with Tamas Darvas and Chinh Lu.[-]

​We give a geometric representation theory proof of a mild version of the Beauville-Voisin Conjecture for Hilbert schemes of K3 surfaces, namely the injectivity of the cycle map restricted to the subring of Chow generated by tautological classes. Although other geometric proofs of this result are known, our approach involves lifting formulas of Lehn and Li-Qin-Wang from cohomology to Chow, and using them to quickly solve the problem by invoking the irreducibility criteria of Virasoro algebra modules, due to Feigin-Fuchs. Joint work with Davesh Maulik.[-]

For complex projective manifolds $X$ of general type, Lang claimed the equivalence between three fields: birational geometry, complex hyperbolicity, and arithmetic. We extend this equivalence to arbitrary $X$'s by introducing the (antithetical) class of “Special” manifolds and constructing the “Core” fibration, the unique one with special fibres and general type “orbifold” base. We conjecture that special manifolds —which are defined algebro-geometrically by a certain non-positivity of their cotangent bundles— are also exactly the ones having Zariski-dense entire curves (so violating the GGL property). We shall give (j.w. J. Winkelmann) some examples supporting this conjecture. The arithmetic aspect will be skipped.[-]

Viehweg and Zuo obtained several results concerning the moduli number in smooth families of polarized varieties with semi-ample canonical class over a quasiprojective base. These results led Viehweg to conjecture that the base of a family of maximal variation is of log-general type, and the conjecture has been recently proved by Campana and Paun.
From the “opposite” side, Taji proved that a smooth projective family over a special (in the sense of Campana) quasiprojective base is isotrivial.
We extend Taji's theorem to quasismooth families, that is, families of leaves of compact foliations without singularities. This is a joint work with F. Campana[-]