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

Let pp be a prime and let Fˉp\bar{\mathbb{F}}_p be an algebraic closure of Fp\mathbb{F}_p. Let ρ:GQGL(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=σωcψ\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

σIp(ωa0ωb),\sigma|_{I_p}\sim\begin{pmatrix}\omega^a&*\\0&\omega^b\end{pmatrix},

choose a,b,ca,b,c modulo p1p-1 with 0<ab,bcp0<a-b,b-c\leq p and 0c<p10\leq c<p-1, imposing ab=pa-b=p when σ\sigma is très ramifiée, and take V=F(a2,b1,c)V=F(a-2,b-1,c); alternatively, choose a,b,ca,b,c with 0<ca,abp0<c-a,a-b\leq p and 0b<p10\leq b<p-1, again imposing ab=pa-b=p when σ\sigma is très ramifiée, and take V=F(c2,a1,b)V=F(c-2,a-1,b). If

σIp(ω2a+bp00ω2a+bp)\sigma|_{I_p}\sim\begin{pmatrix}\omega_2^{a+bp}&0\\0&\omega_2'^{a+bp}\end{pmatrix}

and 0<abp0<a-b\leq p, either choose 0<ab,bcp0<a-b,b-c\leq p, 0c<p10\leq c<p-1, and take V=F(a2,b1,c)V=F(a-2,b-1,c), or choose 0<ca,abp0<c-a,a-b\leq p, 0b<p10\leq b<p-1, and take V=F(c2,a1,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),Vϵ)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.

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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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