Campana's almost abelian fundamental group conjecture for special varieties

Let XX be a special variety. Write π1(X)\pi_1(X) for its fundamental group, and define the maximal irregularity by

q~(X)=sup{q(X~)X~X is finite eˊtale}.\widetilde q(X)=\operatorname{sup}\left\{q(\widetilde X)\mid \widetilde X\to X\text{ is finite étale}\right\}.

Here a group is almost abelian if it contains an abelian subgroup of finite index. Campana's fundamental-group conjecture. One has

  1. π1(X)\pi_1(X) is almost abelian;
  2. if q~(X)=0\widetilde q(X)=0, then π1(X)\pi_1(X) is finite.

The conjecture is motivated by the expectation that special varieties are, in a suitable birational sense, successive extensions of orbifolds with Fano or numerically trivial canonical bundle. The source does not specify a resolution of either assertion.

Sources & referencesView supporting material

Primary source

Frédéric Campana and Benoît Claudon, “Quelques propriétés de stabilité des variétés spéciales”, arXiv:1410.2958 (2014).

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