Ash–Doud conjecture on Galois representations and eigenclasses in the homology of GL⁡(3,Z)\operatorname{GL}(3,\mathbb{Z})

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Let pp be a prime and let Fˉp\bar{\mathbb{F}}_p be an algebraic closure of Fp\mathbb{F}_p. Let ρ:GQ→GL⁡(3,Fˉp)\rho:G_{\mathbb{Q}}\to\operatorname{GL}(3,\bar{\mathbb{F}}_p) be a Galois representation that is a sum of an irreducible odd two-dimensional representation and a character. Let NN be its Serre conductor and let ϵ\epsilon be its nebentype. Write ρ=σ⊕ωcψ\rho=\sigma\oplus\omega^c\psi, where ψ\psi has conductor prime to pp, and let VV be an irreducible admissible Fp[GL⁡(3,Fp)]\mathbb{F}_p[\operatorname{GL}(3,\mathbb{F}_p)]-module. For the specified possibilities for the restriction of σ\sigma to inertia at pp, define VV as follows: if

σ∣Ip∼(ωa∗0ωb),\sigma|_{I_p}\sim\begin{pmatrix}\omega^a&*\\0&\omega^b\end{pmatrix},

choose a,b,ca,b,c modulo p−1p-1 with 0<a−b,b−c≤p0<a-b,b-c\leq p and 0≤c<p−10\leq c<p-1, imposing a−b=pa-b=p when σ\sigma is très ramifiée, and take V=F(a−2,b−1,c)V=F(a-2,b-1,c); alternatively, choose a,b,ca,b,c with 0<c−a,a−b≤p0<c-a,a-b\leq p and 0≤b<p−10\leq b<p-1, again imposing a−b=pa-b=p when σ\sigma is très ramifiée, and take V=F(c−2,a−1,b)V=F(c-2,a-1,b). If

σ∣Ip∼(ω2a+bp00ω2′a+bp)\sigma|_{I_p}\sim\begin{pmatrix}\omega_2^{a+bp}&0\\0&\omega_2'^{a+bp}\end{pmatrix}

and 0<a−b≤p0<a-b\leq p, either choose 0<a−b,b−c≤p0<a-b,b-c\leq p, 0≤c<p−10\leq c<p-1, and take V=F(a−2,b−1,c)V=F(a-2,b-1,c), or choose 0<c−a,a−b≤p0<c-a,a-b\leq p, 0≤b<p−10\leq b<p-1, and take V=F(c−2,a−1,b)V=F(c-2,a-1,b). Ash–Doud conjecture. For every such value of VV, there is an H3,N\mathcal{H}_{3,N}-eigenclass in

H3(Γ0(3,N),V⊗ϵ)H_3(\Gamma_0(3,N),V\otimes\epsilon)

with ρ\rho attached. This predicts that the specified three-dimensional Galois representations occur in the appropriate arithmetic homology with precisely the Serre weights determined by their inertia at pp; the broader framework is related to conjectures for more general representations, while the status of this formulation is not resolved in the supplied source.

References

Primary source

Avner Ash and Darrin Doud, “Reducible Galois representations and the homology of GL(3,Z)”, arXiv:1205.3086 (2012).

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