Seminar Algebra and Geometry: Federico Lo Bianco (Université de Marseille)

Symmetries of foliation: transverse action

We consider a holomorphic (singular) foliation F on a projective manifold X and a group G of birational transformations of X which preserve F (i.e. it permutes the set of leaves). We say that the transverse action of G is finite if some finite index subgroup of G fixes each leaf of F.

I will briefly recall a criterion for the finiteness of the transverse action in the case of algebraically integrable foliations (i.e. foliations whose leaves coincide with the fibres of a fibration). Then I will explain how the presence of certain transverse structures on the foliation allow to recover the same result; in this case, one can study the monodromy of such a structure (which is defined in an analogous way as that of a more familiar (G,X)-structure) and apply factorization results in order to reduce the problem to subvarieties of quotients of the product of unit discs, whose geometry is now quite well understood.

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