English

Normality of monodromy group in generic convolution group

Algebraic Geometry 2025-01-27 v1 Number Theory

Abstract

On an abelian variety AA, sheaf convolution gives a Tannakian formalism for perverse sheaves. Let XX be an irreducible algebraic variety with generic point η\eta. Let KK be a family of perverse sheaves (more precisely, a relative perverse sheaf) on the constant abelian scheme pX:A×XXp_X:A\times X\to X. We show that for uncountably many character sheaves LχL_{\chi} on AA, the monodromy groups of R0pX(KpALχ)R^0p_{X*}(K\otimes p_A^*L_{\chi}) are normal in the Tannakian group G(KAη)G(K|_{A_{\eta}}) of the perverse sheaf KAηPerv(Aη)K|_{A_{\eta}}\in\mathrm{Perv}(A_{\eta}). This result is inspired from and could be compared to two other normality results: In the same setting, the Tannakian group G(KAηˉ)G(K|_{A_{\bar{\eta}}}) is normal in G(KAη)G(K|_{A_{\eta}}) (due to Lawrence-Sawin). For a polarizable variation of Hodge structures, outside a meager locus, the connected monodromy group is normal in the derived Mumford-Tate group (due to Andr\'e).

Keywords

Cite

@article{arxiv.2501.14052,
  title  = {Normality of monodromy group in generic convolution group},
  author = {Haohao Liu},
  journal= {arXiv preprint arXiv:2501.14052},
  year   = {2025}
}

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R2 v1 2026-06-28T21:15:26.813Z