Conjectural description of the isotypic part of cohomology of Shtukas

Let CC be the underlying smooth projective curve, let II be a finite index set with I=r|I|=r, and let fsnfs_n be a geometrically irreducible Weil local system of rank nn on CC. Write fsn\e=iIfsn\eifs_n^{\underline{\e}}=\boxtimes_{i\in I}fs_n^{\e_i} for \e{±1}0r\underline{\e}\in\{\pm1\}^r_0, and let \Sht\GLn,\e\Sht_{\GL_n,\underline{\e}} denote the corresponding Shtuka stack. The notation Γc(\Sht\GLn,\e,\Qlbar)\Loc\GLn,fsn\arith\Gamma_c(\Sht_{\GL_n,\underline{\e}},\underline{\Qlbar})_{\Loc_{\GL_n,fs_n}^{\arith}} denotes the isotypic summand supported on the connected component \Loc\GLn,fsn\arith\Loc_{\GL_n,fs_n}^{\arith}. Conjectural description. For each \e{±1}0r\underline{\e}\in\{\pm1\}^r_0, there is a canonical isomorphism

Γc(\Sht\GLn,\e,\Qlbar)\Loc\GLn,fsn\arith[(n1)r]Γ(CI,fsn\e)\cO(\Loc\GLn,fsn\arith).\Gamma_c(\Sht_{\GL_n,\underline{\e}},\underline{\Qlbar})_{\Loc_{\GL_n,fs_n}^{\arith}}[(n-1)r]\cong \Gamma(C^I,fs_n^{\underline{\e}})\otimes \cO(\Loc_{\GL_n,fs_n}^{\arith}).

In particular,

(d\ZZHc+(n1)r(\Sht\GLn,\ed,\Qlbar))fsnH(CI,fsn\e).(\prod_{d\in\ZZ}H^{*+(n-1)r}_c(\Sht_{\GL_n,\underline{\e}}^d,\underline{\Qlbar}))_{fs_n}\cong H^*(C^I,fs_n^{\underline{\e}}).

This is presented as a conjectural description of the geometric-isotypic contribution to Shtuka cohomology and is related in the source to geometric Langlands with restricted variation; no resolution status is supplied.

Sources & referencesView supporting material

Primary source

Zeyu Wang, “Special Cycle on Shtukas and Categorical Trace”, arXiv:2509.05526 (2025).

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