Plectic comparison conjecture for partial Frobenius and filtrations

Let ff be the Hilbert modular form and let Dp(f)D_p(f) be its pp-adic de Rham cohomology with partial Frobenius operators φ1,,φd\varphi_1,\dots,\varphi_d and partial filtrations Fili\operatorname{Fil}_i^\bullet. Choose a global isomorphism

ψ:Vp(f)(-Ind)(Vpstd(f))\psi: V_p(f)\cong (\bigotimes\text{-Ind})(V_p^{\mathrm{std}}(f))

and let

ψp:Dp(f)i=1dDpi(f)\psi_p:D_p(f)\cong\bigotimes_{i=1}^dD_{\mathfrak{p}_i}(f)

be the induced isomorphism of filtered φ\varphi-modules, where Dpi(f)D_{\mathfrak{p}_i}(f) is the filtered φ\varphi-module of the standard representation at pi\mathfrak{p}_i. Plectic comparison conjecture. For some choice of global isomorphism ψ\psi as above, and each i=1,,di=1,\dots,d, the isomorphism ψp\psi_p intertwines the partial Frobenius φi\varphi_i on Dp(f)D_p(f) with the operator

11φ111\otimes\dots\otimes1\otimes\varphi\otimes1\otimes\dots\otimes1

with φ\varphi in the ii-th component, on iDpi(f)\bigotimes_iD_{\mathfrak{p}_i}(f); similarly, it intertwines the ii-th partial filtration Fili\operatorname{Fil}_i^\bullet on Dp(f)D_p(f) with

Dp1(f)Dpi1(f)(FilDpi(f))Dpi+1(f)Dpd(f).D_{\mathfrak{p}_1}(f)\otimes\dots\otimes D_{\mathfrak{p}_{i-1}}(f)\otimes(\operatorname{Fil}^\bullet D_{\mathfrak{p}_i}(f))\otimes D_{\mathfrak{p}_{i+1}}(f)\otimes\dots\otimes D_{\mathfrak{p}_d}(f).

The conjecture would identify the plectic structures on the cohomology of the Hilbert modular variety with the factorwise structures arising from tensor induction. The preceding partial Eichler--Shimura relation gives compatible polynomial relations for the partial Frobenii, but the simultaneous comparison with the tensor factors and partial filtrations remains conjectural.

Sources & referencesView supporting material

Primary source

David Loeffler and Sarah Livia Zerbes, “Plectic structures in p-adic de Rham cohomology”, arXiv:2211.12078 (2023).

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