Abelianness and strict A1-invariance of connected components of reductive groups

From papers

Let kk be a field and let GG be a reductive algebraic group over kk. Write pi0A1(G)pi_0^{{\mathbb A}^1}(G) for the sheaf of A1{\mathbb A}^1-connected components of GG. A sheaf of groups is strictly A1{\mathbb A}^1-invariant if it is a sheaf of abelian groups and its Nisnevich cohomology presheaves are A1{\mathbb A}^1-invariant in every degree.

Abelianness and strict invariance conjecture. For every reductive group GG over kk, the sheaf π0A1(G)\pi_0^{{\mathbb A}^1}(G) is a sheaf of abelian groups. Moreover, π0A1(G)\pi_0^{{\mathbb A}^1}(G) is strictly A1{\mathbb A}^1-invariant.

This would place the A1{\mathbb A}^1-connected components of every reductive group in the abelian category of strictly A1{\mathbb A}^1-invariant sheaves. The abelianness of these sheaves is stated as an open question in the source, and strict A1{\mathbb A}^1-invariance would then follow from the relevant A1{\mathbb A}^1-homotopy-theoretic results; no general proof is given here.

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Sources & referencesView supporting material

Primary source

Amit Hogadi and Anand Sawant, “Transfers on A^1-connected components of quasi-split groups and the norm principle”, arXiv:2512.15324 (2025).

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