Prasad–Chan same-group Ext conjecture for Arthur type representations

Let FF be a non-archimedean local field, let ΔSL2\Delta\operatorname{SL}_2 denote the diagonally embedded copy of SL2\operatorname{SL}_2 in SL2×SL2\operatorname{SL}_2\times\operatorname{SL}_2, and let A(π){\mathcal A}(\pi) be the Arthur parameter of an irreducible Arthur type representation π\pi of GLn(F)\operatorname{GL}_n(F). Prasad–Chan's conjecture. For irreducible Arthur type representations π1\pi_1 and π2\pi_2 of GLn(F)\operatorname{GL}_n(F),

ExtGLn(F)(π1,π2)0\operatorname{Ext}^*_{\operatorname{GL}_n(F)}(\pi_1,\pi_2)\neq 0

if and only if

A(π1)WF×ΔSL2A(π2)WF×ΔSL2.{\mathcal A}(\pi_1)|_{W_F\times\Delta\operatorname{SL}_2}\cong {\mathcal A}(\pi_2)|_{W_F\times\Delta\operatorname{SL}_2}.

This conjecture characterizes nontrivial extensions between same-group irreducible Arthur type representations by equality of their Arthur parameters after restriction to the Weil group times the diagonal SL2\operatorname{SL}_2; the source gives no resolution.

Sources & referencesView supporting material

Primary source

Mohammed Saad Qadri, “Non-tempered Ext Branching Laws for the p-adic General Linear Group”, arXiv:2402.07423 (2024).

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