Coregularity structure conjecture for regional fundamental groups

Let XX be a rationally connected variety of dimension nn, regularity rr, and coregularity cc. Assume that G:=π1reg(X)G:=\pi_1^{\rm reg}(X) is finite. Coregularity structure conjecture. The group GG admits a subnormal subseries

A0A1A2G,A_0\triangleleft A_1\triangleleft A_2\triangleleft G,

such that A0A_0 acts on either Dr1\mathbb{D}^{r-1} or Sr1S^{r-1}, A1/A0A_1/A_0 is an abelian group of rank at most rr, and A2/A1A_2/A_1 has order at most N(c)N(c), where N(c)N(c) depends only on the coregularity cc.

This decomposes the finite regional fundamental group into contributions from the dual complex, elements fixing its strata, and the minimal log canonical center. The source presents the bound depending only on coregularity as conjectural and open.

Sources & referencesView supporting material

Primary source

Joaquín Moraga, “Coregularity of Fano varieties”, arXiv:2206.10834 (2022).

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