The conjecture on Galois representations attached to automorphic representations of GSp4

Let GG be the group under consideration, let FF be the underlying number field, and let π=ππf\pi=\pi_\infty\otimes\pi_f be an automorphic representation of G(A)G(\mathbb A). For a split prime l=xxl=xx' of FF, let KlK_l be the specified hyperspecial subgroup, let Tl,iT_{l,i} for i{0,1,2}i\in\{0,1,2\} be the corresponding Hecke operators, and let cl,ic_{l,i} be the eigenvalue of Tl,iT_{l,i} on πlKl\pi_l^{K_l}. If πW(λ)\pi_\infty\simeq W(\lambda), write λ\lambda in terms of integers h1>h2>h3>h4h_1>h_2>h_3>h_4 satisfying h1+h4=h2+h3h_1+h_4=h_2+h_3. Galois-representation conjecture. Up to isomorphism, there exists a unique continuous semisimple Galois representation with GSp4\mathrm{GSp}_4-structure

ρπ:GalFGSp4(Qp)\rho_\pi:\mathrm{Gal}_F\rightarrow\mathrm{GSp}_4(\overline{\mathbb Q}_p)

satisfying the following conditions. If l=xxl=xx' splits in FF and ιxπl\iota_x^*\pi_l is unramified, then ρπ\rho_\pi is unramified above ll, and

ı1det(Tidρπ(Frobx))=T4cl,1T3+((l3+l)cl,0+lcl,2)T2l3cl,0cl,1T+l6cl,02\imath^{-1}\mathrm{det}(T\mathrm{id}-\rho_\pi(\mathrm{Frob}_x))=T^4-c_{l,1}T^3+((l^3+l)c_{l,0}+lc_{l,2})T^2-l^3c_{l,0}c_{l,1}T+l^6c_{l,0}^2

and

ı1sim(ρπ(Frobx))=l3cl,0.\imath^{-1}\mathrm{sim}(\rho_\pi(\mathrm{Frob}_x))=l^3c_{l,0}.

If l=xxl=xx' splits in FF, then

ı1WD(ρπGalFx)\imath^{-1}\mathrm{WD}(\rho_\pi\vert_{\mathrm{Gal}_{F_x}})

coincides with ιx(πlsim32)\iota_x^*(\pi_l\otimes\vert\mathrm{sim}\vert^{\frac32}) under the classical local Langlands correspondence. If p=p=\wp\wp' splits in FF, then ρπGalF\rho_\pi\vert_{\mathrm{Gal}_{F_\wp}} is de Rham and

ı1WD(ρπGalF)\imath^{-1}\mathrm{WD}(\rho_\pi\vert_{\mathrm{Gal}_{F_\wp}})

coincides with ι(πpsim32)\iota_\wp^*(\pi_p\otimes\vert\mathrm{sim}\vert^{\frac32}) under the classical local Langlands correspondence. Moreover, if πW(λ)\pi_\infty\simeq W(\lambda), then ρπGalF\rho_\pi\vert_{\mathrm{Gal}_{F_\wp}} has Hodge–Tate weights h1>h2>h3>h4h_1>h_2>h_3>h_4. The conjecture predicts a compatible Galois representation realizing the local Langlands parameters and Hodge–Tate weights of automorphic representations of GG; the supplied text does not state a resolution.

Sources & referencesView supporting material

Primary source

Xiaozheng Han, “p-adic Hodge parameters in the crystalline representations of GSp4”, arXiv:2512.05275 (2025).

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