Essential-image conjecture for the generalized Montréal functor

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Let Δ={α1,…,αn−1}\Delta=\{\alpha_1,\dots,\alpha_{n-1}\}, and let VV be an object of Rep⁡hord⁡(GQp,Δ×Qp×)\operatorname{Rep}^{\operatorname{ord}}_h(G_{\mathbb{Q}_p,\Delta}\times\mathbb{Q}_p^\times). For each α=αj∈Δ\alpha=\alpha_j\in\Delta, let

0=soc⁡0α‾(V)⪇soc⁡1α‾(V)⪇⋯⪇soc⁡rαα‾(V)=V0=\operatorname{soc}_0^{\overline{\alpha}}(V)\lneq\operatorname{soc}_1^{\overline{\alpha}}(V)\lneq\dots\lneq\operatorname{soc}_{r_\alpha}^{\overline{\alpha}}(V)=V

be the socle filtration as a representation of GQp,Δ∖{α}×Qp×G_{\mathbb{Q}_p,\Delta\setminus\{\alpha\}}\times\mathbb{Q}_p^\times, and write griα‾(V)(ηα‾)\mathrm{gr}^{\overline{\alpha}}_i(V)(\eta_{\overline{\alpha}}) for the ηα‾\eta_{\overline{\alpha}}-isotypic component of its iith graded piece, where ηα‾\eta_{\overline{\alpha}} is a character of GQp,Δ∖{α}×Qp×G_{\mathbb{Q}_p,\Delta\setminus\{\alpha\}}\times\mathbb{Q}_p^\times. Let ηα‾~(k)\widetilde{\eta_{\overline{\alpha}}}^{(k)} denote the character associated with the restriction to the kkth copy of GQpG_{\mathbb{Q}_p} for k≠jk\ne j, to the central Qp×\mathbb{Q}_p^\times for k=nk=n, and let ηα‾~(0)\widetilde{\eta_{\overline{\alpha}}}^{(0)} be the trivial character. Essential-image conjecture. The object VV is in the essential image of V∨∘DΔ∨\mathbb{V}^\vee\circ D^\vee_\Delta if and only if, for every α∈Δ\alpha\in\Delta, i∈{1,…,rα}i\in\{1,\dots,r_\alpha\}, and character ηα‾ ⁣:GQp,Δ∖{α}×Qp×→Fq×\eta_{\overline{\alpha}}\colon G_{\mathbb{Q}_p,\Delta\setminus\{\alpha\}}\times\mathbb{Q}_p^\times\to\mathbb{F}_q^\times, the representation griα‾(V)(ηα‾)\mathrm{gr}^{\overline{\alpha}}_i(V)(\eta_{\overline{\alpha}}) is in the image of Colmez's Montréal functor evaluated at a representation π\pi of GL⁡2(Qp)\operatorname{GL}_2(\mathbb{Q}_p) over Fq\mathbb{F}_q with central character

ηα‾~(j+1)ηα‾~(j−1).\frac{\widetilde{\eta_{\overline{\alpha}}}^{(j+1)}}{\widetilde{\eta_{\overline{\alpha}}}^{(j-1)}}.

This conjecture characterizes the essential image of the generalized Montréal functor using the socle filtrations of ordinary mod pp representations; its resolution would give a precise criterion for recognizing objects arising from V∨∘DΔ∨\mathbb{V}^\vee\circ D^\vee_\Delta.

References

Primary source

Gergely Jakovác and Gergely Zábrádi, “Finiteness properties of generalized Montréal functors with applications to mod p representations of GL_n(Q_p)”, arXiv:2501.18396 (2025).

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