§3 · Agent 3 · Hypotheses in char p · 2026-10-18T03:02:13Z
Summary 3.12 · (Q3) verdict: (A1)(A1) Field and group: F a non-archimedean local field of characteristic 0 (Sakellaridis §1.1), G split reductive over O with connected fibres and simply connected derived group (§1.7).–(A3c)(A3c) Iwahori orbits (Sakellaridis's Axiom 2.4.2): xJ ⊆ xB(O) for every X-antidominant torus point x., (A5)(A5) X homogeneous and affine, and the open Borel orbit has a single B(F)-orbit of F-points (§8)., (A4)(A4) Spherical roots and colours: no pair of maximal rank of type N; classical Levis L_γ; Statements 6.3.1 and 7.1.5.(i,ii,iv) hold over \(\mathbb F_q((t))\)
proved audit: correct ★ key step
For \(p\) odd and \(\mathcal M_\theta=(G_{\mathbb Z}/G_{\mathbb Z}^{\theta_0})\otimes\mathbb F_q[[t]]\), every hypothesis of Sakellaridis's Theorem 8.0.2 assigned to (Q3) is proved by characteristic-\(p\) arguments, except Statement 6.3.1, whose combinatorial input is verified and whose analytic part belongs to (Q1). The same proofs work for \(p\)-adic \(F\), \(p\) odd, and remove from S4/S4b the citations of Kneser, Vust/Richardson, Helminck–Wang, Alper, Knop and Helgason.
Summary 3.12.
Invariants in characteristic \(p\ne2\): \(\mathcal X(X)=\mathbb Z\omega_1\oplus\mathbb Z\omega_6\); \(\Lambda_X^+=\Lambda_X\cap\{\langle v,\gamma_1\rangle\le0,\langle v,\gamma_6\rangle\le0\}\); \(\Delta_X=\{\gamma_1,\gamma_6\}\), type \(G\); colours \(D_1,D_6\) with valuations \(\check\gamma_1,\check\gamma_6\); \(W_X\simeq S_3\); 45 maximal-rank orbits; \(\Theta=\check\Phi_X\times\{(+,4)\}\).
- (A1)(A1) Field and group: F a non-archimedean local field of characteristic 0 (Sakellaridis §1.1), G split reductive over O with connected fibres and simply connected derived group (§1.7)., (A2)(A2) Integral model: X quasi-affine over O, its open Borel orbit smooth and surjective over O with B-homogeneous special fibre; a G-eigenmeasure on X and a B-invariant measure on the open orbit (§1.7). (Proposition 3.2): Conrad's Lemma 2.2.4 and Thm 2.3.1, valid over any base, replace Edixhoven and Alper; connectedness of the fibres is proved directly.
- (A5)(A5) X homogeneous and affine, and the open Borel orbit has a single B(F)-orbit of F-points (§8). (Lemma 3.3).
- (A3b)(A3b) Cartan decomposition (Sakellaridis's Axiom 2.4.1): the X-antidominant torus points represent every K-orbit on X(F), and points with distinct labels lie in distinct K-orbits.: \(G(F)=KT(F)H(F)\) by Delorme–Sécherre, whose field hypothesis includes \(\mathbb F_q(\!(t)\!)\) and whose proof was checked (Audit 3.5); one \(H(F)\)-class of maximal \((\theta,F)\)-split tori by a direct argument (Proposition 3.4) using Bruhat–Tits III instead of Kneser; labels through \(\mathcal V\) (Proposition 3.7) and \(W_X\subseteq K\) (Theorem 3.8).
- (A3c)(A3c) Iwahori orbits (Sakellaridis's Axiom 2.4.2): xJ ⊆ xB(O) for every X-antidominant torus point x. (Audit 3.9). (A4)(A4) Spherical roots and colours: no pair of maximal rank of type N; classical Levis L_γ; Statements 6.3.1 and 7.1.5. (Proposition 3.6, Proposition 3.7, Proposition 3.10); remaining: Remark 3.11.
- Consequence, stated but not claimed. If (Q1) supplies Theorem 8.0.2 over \(\mathbb F_q(\!(t)\!)\) under (A1)–(A5)Sakellaridis's standing assumptions for Theorem 8.0.2: (A1) characteristic-0 field and split group; (A2) integral model; (A3a) rank-one models over O, (A3b) Cartan decomposition, (A3c) Iwahori orbits (his Axioms 2.2.1, 2.4.1, 2.4.2); (A4) spherical roots and colours; (A5) homogeneous, affine, one open Borel orbit. (including the analytic part of Statement 6.3.1) and (Q2) supplies (A3a)(A3a) Rank-one models over O (Sakellaridis's Axiom 2.2.1): for every Borel orbit Y of maximal rank and every simple root α, the O-scheme YP_α/R(P_α) is one of the four standard PGL2-spaces over O, with his scheme structure on Y, and YP_α is the closure of its generic fibre minus the closure of the generic boundary. for \(\mathcal M_\theta\) over \(\mathbb F_q[[t]]\), then Proposition VII (\(r\) not onto, every \(q\)) gives that (SG) fails for \(E_6/F_4\) over \(\mathbb F_q(\!(t)\!)\). No hypothesis is verified here by appeal to Theorem 8.0.2 in characteristic \(p\) (checklist item 10).
- Checklist. (1) Each characteristic-0 citation is replaced or shown characteristic-free (Audit 3.1). (2) The arguments use \(2\in\mathcal O^\times\) and separability of \(F(\sqrt t)\), never \(\mathrm{char}\,F=0\). (3) Integral statements are proved as statements about \(\mathcal O\)-schemes (open immersions, purity, torsors), not fibrewise. (5) All stabilizers are smooth. (6) Only \(H^1\) of \(\mathrm{Spin}_8\), \(F_4\), split tori and split unipotent groups is used. (8) The dictionary \(\Lambda_X^+\leftrightarrow\Lambda_S^+\) is explicit (Theorem 3.8 step 1). (9) No 'almost every place'. (11) \(p=3\) needs no change (Audit 3.1 step 2).
Builds on
- Audit 3.1 · Where the \(p\)-adic verification (S4, S4b) used characteristic 0, and what replaces it
- Proposition 3.2 · (A1)(A1) Field and group: F a non-archimedean local field of characteristic 0 (Sakellaridis §1.1), G split reductive over O with connected fibres and simply connected derived group (§1.7)., (A2)(A2) Integral model: X quasi-affine over O, its open Borel orbit smooth and surjective over O with B-homogeneous special fibre; a G-eigenmeasure on X and a B-invariant measure on the open orbit (§1.7). for \(\mathcal M_\theta\) over any complete DVR with 2 invertible
- Lemma 3.3 · (A5)(A5) X homogeneous and affine, and the open Borel orbit has a single B(F)-orbit of F-points (§8). and Galois cohomology over \(\mathbb F_q((t))\): \(X(F)=G(F)x_0\), \(X_F\) affine
- Proposition 3.4 · Maximal \(\theta\)-split tori: dimension 2, one \(H(F)\)-class (residue char. \(\ne2\))
- Audit 3.5 · Delorme–Sécherre over \(\mathbb F_q((t))\), \(p\) odd: \(G(F)=H(F)T(F)K\)
- Proposition 3.6 · Char \(\ne2\): 45 maximal-rank Borel orbits \(Bn_wx_0\), all pairs of type \(G\) or \(U\)
- Proposition 3.7 · Char \(\ne2\): two colours, the valuation cone, spherical roots \(\gamma_1,\gamma_6\)
- Theorem 3.8 · (A3b)(A3b) Cartan decomposition (Sakellaridis's Axiom 2.4.1): the X-antidominant torus points represent every K-orbit on X(F), and points with distinct labels lie in distinct K-orbits. for \(\mathcal M_\theta\) over \(\mathbb F_q((t))\): \(K\backslash X(F)\simeq\Lambda_X^+\)
- Audit 3.9 · Axiom 2.4.2Sakellaridis's Axiom 2.4.2, relabelled (A3c): Iwahori orbits at the antidominant torus points. for \(\mathcal M_\theta\) over \(\mathbb F_q((t))\): S4-5 re-checked
- Proposition 3.10 · (A4)(A4) Spherical roots and colours: no pair of maximal rank of type N; classical Levis L_γ; Statements 6.3.1 and 7.1.5. in char \(p\): (i), (ii), Statement 7.1.5, and the combinatorics of 6.3.1
- Remark 3.11 · Not proved here: the analytic part of Statement 6.3.1 over \(\mathbb F_q((t))\)
Built on by
- Theorem 7.4 · Verdict: Sakellaridis's theorem over \(\mathbb F_q(\!(t)\!)\); for \(E_6/F_4\) in both characteristics, (A3a)(A3a) Rank-one models over O (Sakellaridis's Axiom 2.2.1): for every Borel orbit Y of maximal rank and every simple root α, the O-scheme YP_α/R(P_α) is one of the four standard PGL2-spaces over O, with his scheme structure on Y, and YP_α is the closure of its generic fibre minus the closure of the generic boundary. included
Sources
- sakellaridis-v3.pdf, Theorem 8.0.2 p. 64 and its hypotheses (§1.1, §1.7, Axioms 2.2.1–2.4.2, §6 opening, §7, §8)
- S4.json, S4b.json
- e6-f4-module.html (Proposition VII)