Irreducibility conjecture for reductions at the boundary of weight space

Let ff be a newform of weight k2k\geq 2 and level Γ1(Npr)\Gamma_1(Np^r), where r2r\geq 2, whose character has pp-part χ\chi of conductor prp^r, and let α\alpha be its UpU_p-eigenvalue. Let Vk,α,χV_{k,\alpha,\chi} be the associated local Galois representation and let Vk,α,χ\overline{V}_{k,\alpha,\chi} be the semisimplification of its mod-pp reduction. Normalize the valuation vχv_\chi so that its image on Qp(χ)×{\mathbb{Q}}_p(\chi)^\times is Z{\mathbb{Z}}.

Boundary irreducibility conjecture. If vχ(α)Zv_\chi(\alpha)\notin{\mathbb{Z}}, then Vk,α,χ\overline{V}_{k,\alpha,\chi} is irreducible.

This local assertion is proposed to explain patterns in the slopes of forms near the boundary of weight space. The source notes that several global results instead force integral slopes in particular levels, but does not resolve the general conjecture.

Sources & referencesView supporting material

Primary source

Kevin Buzzard and Toby Gee, “Slopes of modular forms”, arXiv:1502.02518 (2016).

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