Essential-image conjecture for the generalized Montréal functor

From papers

Let Δ={α1,,αn1}\Delta=\{\alpha_1,\dots,\alpha_{n-1}\}, and let VV be an object of Rephord(GQp,Δ×Qp×)\operatorname{Rep}^{\operatorname{ord}}_h(G_{\mathbb{Q}_p,\Delta}\times\mathbb{Q}_p^\times). For each α=αjΔ\alpha=\alpha_j\in\Delta, let

0=soc0α(V)soc1α(V)socrαα(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 kjk\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 VDΔ\mathbb{V}^\vee\circ D^\vee_\Delta if and only if, for every αΔ\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 GL2(Qp)\operatorname{GL}_2(\mathbb{Q}_p) over Fq\mathbb{F}_q with central character

ηα~(j+1)ηα~(j1).\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 VDΔ\mathbb{V}^\vee\circ D^\vee_\Delta.

Progress summary

Nothing recorded yet. Refresh searches the literature and the public web for attempts on this problem, and writes the first summary here.

Sources & referencesView supporting material

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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