Connected-component bijection for Hodge–Newton irreducible affine Deligne–Lusztig varieties

Let GG be the reductive group, LL its relevant local field extension, PP the parahoric subgroup, λ\lambda a coweight, and bG(L)b\in G(L). Let X(λ,b)PX(\lambda,b)_P be the associated closed affine Deligne–Lusztig variety, let π0(X(λ,b)P)\pi_0(X(\lambda,b)_P) denote its set of connected components, and let

ηG:G(L)/Pπ1(G)\eta_G:G(L)/P\to\pi_1(G)

be the natural projection. Assume that (λ,b)(\lambda,b) is Hodge–Newton irreducible. Connected-component bijection. The map ηG\eta_G induces a bijection

π0(X(λ,b)P)(σ1)1(ηG(tλ)ηG(b))π1(G).\pi_0(X(\lambda,b)_P)\cong (\sigma-1)^{-1}(\eta_G(t^\lambda)-\eta_G(b))\subseteq\pi_1(G).

This gives an explicit description of the connected components in the Hodge–Newton irreducible case, completing the third step of the paper’s reduction to adjoint simple groups and Hodge–Newton indecomposable pairs. The supplied text does not state whether the claim has been proved or remains conjectural.

Sources & referencesView supporting material

Primary source

Ling Chen and Sian Nie, “Connected components of closed affine Deligne-Lusztig varieties”, arXiv:1703.02476 (2017).

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