Larsen's Galois maximality conjecture for compatible systems

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Let KK be a finitely generated field, let XX be a smooth projective variety over KK, and consider a \mathdsQ\mathds{Q}-compatible system of Galois representations

{ρℓ ⁣:GK→GL⁡(H⁡eˊt⁡i(XK‾,\mathdsQℓ))}.\{\rho_{\ell} \colon G_K \to \operatorname{GL}(\operatorname{H}^{i}_{\operatorname{\acute{e}t}}(X_{\overline{K}},\mathds{Q}_{\ell}))\}.

Let Gℓsc⁡\mathbf{G}_{\ell}^{\operatorname{sc}} be the simply connected cover of the adjoint algebraic monodromy group, and let Γℓsc⁡\Gamma_{\ell}^{\operatorname{sc}} be the inverse image of the adjoint Galois image in Gℓsc⁡(\mathdsQℓ)\mathbf{G}_{\ell}^{\operatorname{sc}}(\mathds{Q}_{\ell}). Larsen's Galois maximality conjecture. For all sufficiently large primes ℓ\ell, Γℓsc⁡\Gamma_{\ell}^{\operatorname{sc}} is a maximal compact subgroup of Gℓsc⁡(\mathdsQℓ)\mathbf{G}_{\ell}^{\operatorname{sc}}(\mathds{Q}_{\ell}). Moreover, it is hyperspecial: there exists a smooth affine group scheme Gℓsc⁡\mathscr{G}_{\ell}^{\operatorname{sc}} over \mathdsZℓ\mathds{Z}_{\ell} such that

Gℓsc⁡(\mathdsZℓ)=Γℓsc⁡.\mathscr{G}_{\ell}^{\operatorname{sc}}(\mathds{Z}_{\ell})=\Gamma_{\ell}^{\operatorname{sc}}.

This is presented as a weaker form of the Galois maximality conjecture for arbitrary smooth projective varieties. The supplied text gives no resolution status for this assertion.

References

Primary source

Zhichao Tang and Haitao Zou, “Monodromy rank and the semisimple Mumford-Tate conjecture for hyper-Kähler varieties”, arXiv:2602.19835 (2026).

Additional references

2 papers in this index state this conjecture (2017–2026). The statement above is taken from the most recent of them; the others are arXiv:1707.07366.

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