The fundamental-group conjecture for open Richardson varieties

Let GG be a semisimple algebraic group with Weyl group WW, simple roots Δ\Delta, and flag variety G/BG/B. For vWv\in W, let X˚idv\mathring X_{\operatorname{{\rm id}}}^v denote the open Richardson variety, and define

Γ(v)=αΔsαv.\Gamma(v)=\\{\alpha\in\Delta\mid s_\alpha\leq v\\}.

Fundamental-group conjecture. For every vWv\in W,

π1(X˚idv)=ZΓ(v).\pi_1(\mathring X_{\operatorname{{\rm id}}}^v)=\mathbb{Z}^{|\Gamma(v)|}.

This expectation arises by viewing X˚idv\mathring X_{\operatorname{{\rm id}}}^v as the complement in the affine space C(v)\mathbb{C}^{\ell(v)} of the Richardson divisors XsαvX_{s_\alpha}^v for αΓ(v)\alpha\in\Gamma(v). The proposed description of the fundamental group depends on the corresponding general affine-plane sections satisfying the stated smoothness and transversality hypotheses; the source provides no resolution of the expectation.

Sources & referencesView supporting material

Primary source

Changzheng Li, Frank Sottile and Chi Zhang, “On the fundamental group of open Richardson varieties”, arXiv:1911.11748 (2020).

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