Categorical trace conjecture for the diagonal correspondence

Let HH be a reductive group, let G=H×HG=H\times H, and let X=H\(H×H)X=H\backslash(H\times H). Let c:HHc:H\to H be the Cartan involution and let fsHfs_H be a local system on the dual group. Set fs=(fsH,cfsH)fs=(fs_H,c^*fs_H) and choose a Hecke eigensheaf \LLfsH\LL_{fs_H} on \BunH\Bun_H. Its Verdier dual \DD(\LLfsH)\DD(\LL_{fs_H}) is a Hecke eigensheaf with eigenvalue cfsHc^*fs_H, and set \LLfs=\LLfsH\DD(\LLfsH)\LL_{fs}=\LL_{fs_H}\boxtimes\DD(\LL_{fs_H}). Let eπ1(H)e\in\pi_1(H), let VHRep(\HcI)V_H\in\operatorname{Rep}(\Hc^I) be irreducible, and put VI=VHIVHIV^I=V_H^I\boxtimes V_H^I. Let ξfs,Ie:VfsIlH,I,!(ICVHI\ShtH,Ie)lH,I,!(ICVHI\ShtH,Ie)\xi_{fs,I}^e:V_{fs}^I\to l_{H,I,!}(\operatorname{IC}_{V_H^I}|_{\Sht_{H,I}^e})\otimes l_{H,I,!}(\operatorname{IC}_{V_H^I}|_{\Sht_{H,I}^e}) be the isotypic-part map, and let \frc\frc be the diagonal cohomological correspondence induced by the Hecke stack. Write \evVH,fsHI:VfsIVH,fsHIVH,fsHI\ukCI\ev_{V_{H,fs_H}^I}:V_{fs}^I\cong V_{H,fs_H}^I\otimes V_{H,fs_H}^{I*}\to\uk_{C^I} for evaluation. Categorical trace conjecture.

\tr\Sht,CI(\frc)ξfs,Ie=\tr(\Frob,Γc(\LLfsHe\DD(\LLfsHe)))\evVH,fsHI.\tr_{\Sht,C^I}(\frc)\circ\xi_{fs,I}^e=\tr(\Frob,\Gamma_c(\LL_{fs_H}^e\otimes\DD(\LL_{fs_H}^e)))\cdot\ev_{V_{H,fs_H}^I}.

This predicts that the trace of the diagonal correspondence on the Shtuka isotypic part is the Frobenius trace on the compactly supported cohomology of the eigensheaf tensor its Verdier dual, multiplied by the natural representation-theoretic evaluation map. The supplied context gives no resolution status.

Sources & referencesView supporting material

Primary source

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

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