Startseite On the Rapoport--Zink space for GU(2, 4) over a ramified prime
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On the Rapoport--Zink space for GU(2, 4) over a ramified prime

  • Stefania Trentin ORCID logo EMAIL logo
Veröffentlicht/Copyright: 11. Juli 2025

Abstract

In this work, we study the supersingular locus of the Shimura variety associated to the unitary group GU ( 2 , 4 ) over a ramified prime. We show that the associated Rapoport–Zink space is flat, and we give an explicit description of the irreducible components of the reduction modulo 𝑝 of the basic locus. In particular, we show that these are universally homeomorphic to either a generalized Deligne–Lusztig variety for a symplectic group or to the closure of a vector bundle over a classical Deligne–Lusztig variety for an orthogonal group. Our results are confirmed in the group-theoretical setting by the reduction method à la Deligne and Lusztig and the study of the admissible set.

Award Identifier / Grant number: 770936

Award Identifier / Grant number: 390685587

Award Identifier / Grant number: 444845124

Funding statement: I was supported by the ERC Consolidator Grant 770936: NewtonStrat, by the Ada Lovelace Fellowship of the Cluster of Mathematics Münster funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy EXC 2044 – 390685587, Mathematics Münster: Dynamics-Geometry-Structure, and by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through the Collaborative Research Center TRR326 “Geometry and Arithmetic of Uniformized Structures”, project number 444845124.

A The Gröbner basis of Proposition 2.6

We list here the polynomials of the Gröbner basis 𝐺 used in the proof of Proposition 2.6. To make the notation more readable and the lexicographic order more intuitive, we have substituted the variables x i j of Proposition 2.3 with the twenty-one letters of the Italian alphabet. The symmetric matrix 𝑋 used in the proof of Proposition 2.6 becomes in the new notation the following matrix with entries in F p [ a , b , , z ] :

X = ( a b c d e f b g h i l m c h n o p q d i o r s t e l p s u v f m q t v z ) .

The monomial order is then simply the usual alphabetical order. We list here the elements of the Gröbner basis used in the proof of Proposition 2.6 and already divide them into the subsets G i j according to Lemma 2.11. We also frame the distinguished generators used in the last part of the proof.

Table 1
G 11 = G a a + g + n + r + u + z

G 12 = G b b 2 + g 2 + h 2 + i 2 + l 2 + m 2
b c + g h + h n + i o + l p + m q
b d + g i + h o + i r + l s + m t
b e + g l + h p + i s + l u + m v
b f + g m + h q + i t + l v + m z
b h c g c r c u c z + d o + e p + f q
b i + c o d g d n d u d z + e s + f t
b l + c p + d s e g e n e r e z + f v
b m + c q + d t + e v f g f n f r f u
b n + b r + b u + b z c h d i e l f m
b o 2 + b r 2 + b s 2 + b t 2 c i o d h o + d i n d i r + d i u + d i z d l s d m t e i s f i t
b o p + b r s + b s u + b t v c l o d h p d i s + d l n + e i z e l s e m t f i v
b o q + b r t + b t u + b t z c m o d h q d i t + d m n e l t f m t
b o s b p r d h s + d i p + e h r e i o
b o t b q r d h t + d i q + f h r f i o
b o u b p s d h u + d l p + e h s e l o
b o v b q s d h v + d m p + e i q e m o + f h s f i p
b o z b q t d h z + d m q + f h t f m o
b p 2 + b s 2 + b u 2 + b v 2 c l p d l s e h p e i s + e l n + e l r e l u + e l z e m v f l v
b p q + b s t + b u v + b v z c m p d m s e h q e i t e l v + e m n + e m r f m v
b p t b q s e h t + e i q + f h s f i p
b p v b q u e h v + e l q + f h u f l p
b p z b q v e h z + e m q + f h v f m p
b q 2 + b t 2 + b v 2 + b z 2 c m q d m t e m v f h q f i t f l v + f m n + f m r + f m u f m z
b r u b s 2 d i u + d l s + e i s e l r
b r v b s t d i v + d m s + e i t e m r
b r z b t 2 d i z + d m t + f i t f m r
b s v b t u e i v + e l t + f i u f l s
b s z b t v e i z + e m t + f i v f m s
b u z b v 2 e l z + e m v + f l v f m u

G 13 = G c c 2 + h 2 + n 2 + o 2 + p 2 + q 2
c d + h i + n o + o r + p s + q t
c e + h l + n p + o s + p u + q v
c f + h m + n q + o t + p v + q z
c g i + c h o + c i r + c l s + c m t d g h d h n d i o d l p d m q
c g l + c h p + c l r + c l u + c m v + d h s d l o e g h e h n e h r e l p e m q
c g m + c h q + c m r + c m u + c m z + d h t d m o + e h v e m p f g h f h n f h r f h u f m q
c h i + c n o + c o r + c p s + c q t d h 2 d n 2 d o 2 d p 2 d q 2
c h l + c n p + c p r + c p u + c q v + d n s d o p e h 2 e n 2 e n r e p 2 e q 2
c h m + c n q + c q r + c q u + c q z + d n t d o q + e n v e p q f h 2 f n 2 f n r f n u f q 2
c h o 2 + c h r 2 + c h s 2 + c h t 2 c i n o c i o r c l p r c m q r d h n o d h o r 2 d h p s 2 d h q t + d i n 2 + d i o 2 d i s 2 d i t 2 d i u 2 2 d i v 2 d i z 2 + 2 d l o p + d l r s + d l s u + 2 d m o q + d m r t + 2 d m t u + d m t z + e h p r + e i r s + e i s u + 2 e i t v e l o 2 e l r 2 e l s 2 e l t 2 + e m r v 2 e m s t + f h q r + f i r t + f i t z + f l r v f m o 2 f m r 2 2 f m r u + f m s 2 f m t 2
c h o p + c h r s + c h s u + c h t v c l n o c l o r c l p s c m q s d h n p d h p r d h p u d h q v d i n s + d i o p + d l n 2 + d l n r + d l p 2 + d m p q e h q t e i t 2 e i v 2 e i z 2 + e m o q + e m r t + e m s v + e m t z + f h q s + f i s t + f i u v + f i v z f m o p f m r s f m s u f m t v
c h o q + c h r t + c h t u + c h t z c m n o c m o r c m p s c m q t d h n q d h q r d h q u d h q z d i n t + d i o q + d m n 2 + d m n r + d m p 2 + d m q 2 e l n t + e l o q + e m n s e m o p
c h p 2 + c h s 2 + c h u 2 + c h v 2 c l n p c l p r c l p u c m q u d l n s + d l o p e h n p e h p r e h p u 2 e h q v e i n s + e i o p + e l n 2 + 2 e l n r e l o 2 + e l p 2 e l t 2 e l v 2 e l z 2 + 2 e m p q + e m s t + e m u v + e m v z + f h q u + f l s t + f l u v + f l v z f m p 2 f m s 2 f m u 2 f m v 2
c h p q + c h s t + c h u v + c h v z c m n p c m p r c m p u c m q v d m n s
+ d m o p e h n q e h q r e h q u e h q z e i n t + e i o q e l n v + e l p q
+ e m n 2 + 2 e m n r + e m n u e m o 2 + e m q 2
c h q 2 + c h t 2 + c h v 2 + c h z 2 c m n q c m q r c m q u c m q z d m n t + d m o q e m n v + e m p q f h n q f h q r f h q u f h q z f i n t + f i o q f l n v + f l p q + f m n 2 + 2 f m n r + 2 f m n u f m o 2 f m p 2 + f m q 2
c i 2 + c o 2 + c r 2 + c s 2 + c t 2 d h i d n o d o r d p s d q t
c i l + c o p + c r s + c s u + c t v e h i e n o e o r e p s e q t
c i m + c o q + c r t + c t u + c t z + e o v e p t f h i f n o f o r f o u f q t
c i p c l o d h p + d l n + e h o e i n
c i q c m o d h q + d m n + f h o f i n
c i s c l r d h s + d l o + e h r e i o
c i t c m r d h t + d m o + f h r f i o
c i u c l s d h u + d l p + e h s e i p
c i v c m s d h v + d m p + f h s f i p
c i z c m t d h z + d m q + f h t f i q
c l 2 + c p 2 + c s 2 + c u 2 + c v 2 e h l e n p e o s e p u e q v
c l m + c p q + c s t + c u v + c v z f h l f n p f o s f p u f q v
c l q c m p e h q + e m n + f h p f l n
c l t c m s e h t + e m o + f h s f l o
c l v c m u e h v + e m p + f h u f l p
c l z c m v e h z + e m q + f h v f l q
c m 2 + c q 2 + c t 2 + c v 2 + c z 2 f h m f n q f o t f p v f q z
c o s c p r d n s + d o p + e n r e o 2
c o t c q r d n t + d o q + f n r f o 2
c o u c p s d n u + d p 2 + e n s e o p
c o v c q s d n v + d p q + f n s f o p
c o z c q t d n z + d q 2 + f n t f o q
c p t c q s e n t + e o q + f n s f o p
c p v c q u e n v + e p q + f n u f p 2
c p z c q v e n z + e q 2 + f n v f p q
c r u c s 2 d o u + d p s + e o s e p r
c r v c s t d o v + d q s + e o t e q r
c r z c t 2 d o z + d q t + f o t f q r
c s v c t u e o v + e p t + f o u f p s
c s z c t v e o z + e q t + f o v f q s
c u z c v 2 e p z + e q v + f p v f q u

G 14 = G d d 2 + i 2 + o 2 + r 2 + s 2 + t 2
d e + i l + o p + r s + s u + t v
d f + i m + o q + r t + s v + t z
d g l + d h p + d i s + d l u + d m v e g i e h o e i r e l s e m t
d g m + d h q + d i t + d m u + d m z + e i v e m s f g i f h o f i r f i u f m t
d h l + d n p + d o s + d p u + d q v e h i e n o e o r e p s e q t
d h m + d n q + d o t + d q u + d q z + e o v e q s f h i f n o f o r f o u f q t
d h o p + d h r s + d h s u + d h t v d i n p d i o s d i p u d i q v e h o 2 e h r 2 e h s 2 e h t 2 + e i n o + e i o r + e i p s + e i q t
d h o q + d h r t + d h t u + d h t z d i n q d i o t d i q u d i q z e l o t + e l q r f h o 2 f h r 2 f h s 2 f h t 2 + f i n o + f i o r + f i p s + f i q t + f l o s f l p r
d h p 2 + d h s 2 + d h u 2 + d h v 2 d l n p d l o s d l p u d m q u e h o p e h r s e h s u e h t v e i q v + e l n o + e l o r + e l p s + e l q t + e m q s + f i q u f l q s
d h p q + d h s t + d h u v + d h v z d m n p d m o s d m p u d m q v e i n q e i o t e i q u e i q z e l o v + e l q s + e m n o + e m o r + e m o u + e m q t f h o p f h r s f h s u f h t v + f i n p + f i o s + f i p u + f i q v
d h q 2 + d h t 2 + d h v 2 + d h z 2 d m n q d m o t d m q u d m q z e m o v + e m q s f h o q f h r t f h t u f h t z f l o v + f l p t + f m n o + f m o r + 2 f m o u f m p s + f m q t
d i l + d o p + d r s + d s u + d t v e i 2 e o 2 e r 2 e s 2 e t 2
d i m + d o q + d r t + d t u + d t z + e r v e s t f i 2 f o 2 f r 2 f r u f t 2
d i p 2 + d i s 2 + d i u 2 + d i v 2 d l o p d l r s d l s u d m t u e i o p e i r s e i s u 2 e i t v + e l o 2 + e l r 2 + e l s 2 + e l t 2 + e m s t + f i t u f l s t
d i p q + d i s t + d i u v + d i v z d m o p d m r s d m s u d m t v e i o q e i r t e i t u e i t z e l r v + e l s t + e m o 2 + e m r 2 + e m r u + e m t 2
d i q 2 + d i t 2 + d i v 2 + d i z 2 d m o q d m r t d m t u d m t z e m r v + e m s t f i o q f i r t f i t u f i t z f l r v + f l s t + f m o 2 + f m r 2 + 2 f m r u f m s 2 + f m t 2
d l 2 + d p 2 + d s 2 + d u 2 + d v 2 e i l e o p e r s e s u e t v
d l m + d p q + d s t + d u v + d v z f i l f o p f r s f s u f t v
d l q d m p e i q + e m o + f i p f l o
d l t d m s e i t + e m r + f i s f l r
d l v d m u e i v + e m s + f i u f l s
d l z d m v e i z + e m t + f i v f l t
d m 2 + d q 2 + d t 2 + d v 2 + d z 2 f i m f o q f r t f s v f t z
d p t d q s e o t + e q r + f o s f p r
d p v d q u e o v + e q s + f o u f p s
d p z d q v e o z + e q t + f o v f p t
d s v d t u e r v + e s t + f r u f s 2
d s z d t v e r z + e t 2 + f r v f s t
d u z d v 2 e s z + e t v + f s v f t u

G 15 = G e e 2 + l 2 + p 2 + s 2 + u 2 + v 2
e f + l m + p q + s t + u v + v z
e g m + e h q + e i t + e l v + e m z f g l f h p f i s f l u f m v
e h m + e n q + e o t + e p v + e q z f h l f n p f o s f p u f q v
e h o q + e h r t + e h t u + e h t z e i n q e i o t e i q u e i q z e l p t + e l q s f h o p f h r s f h s u f h t v + f i n p + f i o s + f i p u + f i q v
e h p q + e h s t + e h u v + e h v z e l n q e l o t e l p v e l q z f h p 2 f h s 2 f h u 2 f h v 2 + f l n p + f l o s + f l p u + f l q v
e h q 2 + e h t 2 + e h v 2 + e h z 2 e m n q e m o t e m p v e m q z f h p q f h s t f h u v f h v z + f m n p + f m o s + f m p u + f m q v
e i m + e o q + e r t + e s v + e t z f i l f o p f r s f s u f t v
e i p q + e i s t + e i u v + e i v z e l o q e l r t e l s v e l t z f i p 2 f i s 2 f i u 2 f i v 2 + f l o p + f l r s + f l s u + f l t v
e i q 2 + e i t 2 + e i v 2 + e i z 2 e m o q e m r t e m s v e m t z f i p q f i s t f i u v f i v z + f m o p + f m r s + f m s u + f m t v
e l m + e p q + e s t + e u v + e v z f l 2 f p 2 f s 2 f u 2 f v 2
e l q 2 + e l t 2 + e l v 2 + e l z 2 e m p q e m s t e m u v e m v z f l p q f l s t f l u v f l v z + f m p 2 + f m s 2 + f m u 2 + f m v 2
e m 2 + e q 2 + e t 2 + e v 2 + e z 2 f l m f p q f s t f u v f v z

G 16 = G f f 2 + m 2 + q 2 + t 2 + v 2 + z 2

G 22 = G g g n + g r + g u + g z h 2 i 2 l 2 m 2 + n r + n u + n z o 2 p 2 q 2 + r u + r z s 2 t 2 + u z v 2
g o 2 + g r 2 + g s 2 + g t 2 2 h i o + i 2 n i 2 r + i 2 u + i 2 z 2 i l s 2 i m t + n r 2 + n s 2 + n t 2 o 2 r + o 2 u + o 2 z 2 o p s 2 o q t + r 2 u + r 2 z r s 2 r t 2 + s 2 z 2 s t v + t 2 u
g o p + g r s + g s u + g t v h i p h l o i 2 s + i l n + i l z i m v l 2 s l m t + n r s + n s u + n t v o 2 s + o p z o q v p 2 s p q t + r s u + r s z s 3 s t 2 + s u z s v 2
g o q + g r t + g t u + g t z h i q h m o i 2 t + i m n l 2 t m 2 t + n r t + n t u + n t z o 2 t p 2 t q 2 t + r t u + r t z s 2 t t 3 + t u z t v 2
g o s g p r h i s + h l r + i 2 p i l o
g o t g q r h i t + h m r + i 2 q i m o
g o u g p s h i u + h l s + i l p l 2 o
g o v g q s h i v + h m s + i l q l m o
g o z g q t h i z + h m t + i m q m 2 o
g p 2 + g s 2 + g u 2 + g v 2 2 h l p 2 i l s + l 2 n + l 2 r l 2 u + l 2 z 2 l m v + n s 2 + n u 2 + n v 2 2 o p s + p 2 r p 2 u + p 2 z 2 p q v + r u 2 + r v 2 s 2 u + s 2 z 2 s t v + u 2 z u v 2
g p q + g s t + g u v + g v z h l q h m p i l t i m s l 2 v + l m n + l m r m 2 v + n s t + n u v + n v z o p t o q s p 2 v + p q r q 2 v + r u v + r v z s 2 v t 2 v + u v z v 3
g p t g q s h l t + h m s + i l q i m p
g p v g q u h l v + h m u + l 2 q l m p
g p z g q v h l z + h m v + l m q m 2 p
g q 2 + g t 2 + g v 2 + g z 2 2 h m q 2 i m t 2 l m v + m 2 n + m 2 r + m 2 u m 2 z + n t 2 + n v 2 + n z 2 2 o q t 2 p q v + q 2 r + q 2 u q 2 z + r v 2 + r z 2 2 s t v + t 2 u t 2 z + u z 2 v 2 z
g r u g s 2 i 2 u + 2 i l s l 2 r
g r v g s t i 2 v + i l t + i m s l m r
g r z g t 2 i 2 z + 2 i m t m 2 r
g s v g t u i l v + i m u + l 2 t l m s
g s z g t v i l z + i m v + l m t m 2 s
g u z g v 2 l 2 z + 2 l m v m 2 u

G 23 = G h h 2 o 2 + h 2 r 2 + h 2 s 2 + h 2 t 2 2 h i n o 2 h i o r 2 h i p s 2 h i q t + i 2 n 2 + i 2 o 2 i 2 s 2 i 2 t 2 i 2 u 2 2 i 2 v 2 i 2 z 2 + 2 i l o p + 2 i l r s + 2 i l s u + 2 i l t v + 2 i m o q + 2 i m r t + 2 i m t u + 2 i m t z l 2 o 2 l 2 r 2 l 2 s 2 l 2 t 2 + 2 l m r v 2 l m s t m 2 o 2 m 2 r 2 2 m 2 r u + m 2 s 2 m 2 t 2 + n 2 r 2 + n 2 s 2 + n 2 t 2 2 n o 2 r 2 n o p s 2 n o q t + o 4 + o 2 p 2 + o 2 q 2 o 2 u 2 2 o 2 v 2 o 2 z 2 + 2 o p s u + 2 o p t v + 2 o q t u + 2 o q t z p 2 s 2 + 2 p q r v 4 p q s t 2 q 2 r u + 2 q 2 s 2 q 2 t 2 r 2 u 2 2 r 2 v 2 r 2 z 2 + 2 r s 2 u + 4 r s t v + 2 r t 2 z s 4 2 s 2 t 2 s 2 v 2 s 2 z 2 + 2 s t u v + 2 s t v z t 4 t 2 u 2 t 2 v 2
h 2 o p + h 2 r s + h 2 s u + h 2 t v h i n p h i p r h i p u h i q v h l n o h l o r h l p s h l q t i 2 n s + i 2 o p + i l n 2 + i l n r + i l p 2 i l t 2 i l v 2 i l z 2 + i m p q + i m s t + i m u v + i m v z + l m o q + l m r t + l m s v + l m t z m 2 o p m 2 r s m 2 s u m 2 t v + n 2 r s + n 2 s u + n 2 t v n o 2 s n o p r n o p u n o q v n p 2 s n p q t + o 3 p + o 2 s u + o 2 t v + o p 3 + o p q 2 o p r u o p s 2 o p t 2 o p v 2 o p z 2 o q r v + o q u v + o q v z + p 2 r s + p 2 t v + p q r t p q t u + p q t z q 2 t v r s v 2 r s z 2 + r t u v + r t v z + s 2 t v s t 2 u + s t 2 z s u z 2 + s v 2 z t 3 v + t u v z t v 3
h 2 o q + h 2 r t + h 2 t u + h 2 t z h i n q h i q r h i q u h i q z h m n o h m o r h m p s h m q t i 2 n t + i 2 o q + i m n 2 + i m n r + i m p 2 + i m q 2 l 2 n t + l 2 o q + l m n s l m o p + n 2 r t + n 2 t u + n 2 t z n o 2 t n o q r n o q u n o q z n p 2 t n q 2 t + o 3 q + o 2 t u + o 2 t z + o p 2 q 2 o p s t + o q 3 o q r u o q r z + o q s 2 o q t 2 + p 2 r t + p 2 t z p q s z p q t v + q 2 r t + q 2 s v
h 2 p 2 + h 2 s 2 + h 2 u 2 + h 2 v 2 2 h l n p 2 h l p r 2 h l p u 2 h l q v 2 i l n s + 2 i l o p + l 2 n 2 + 2 l 2 n r l 2 o 2 + l 2 p 2 l 2 t 2 l 2 v 2 l 2 z 2 + 2 l m p q + 2 l m s t + 2 l m u v + 2 l m v z m 2 p 2 m 2 s 2 m 2 u 2 m 2 v 2 + n 2 s 2 + n 2 u 2 + n 2 v 2 2 n o p s 2 n p 2 u 2 n p q v + o 2 p 2 + o 2 u 2 + o 2 v 2 2 o p s u 2 o q t u + p 4 + p 2 q 2 + p 2 s 2 p 2 t 2 p 2 z 2 2 p q r v + 4 p q s t + 2 p q v z + 2 q 2 r u 2 q 2 s 2 q 2 v 2 s 2 v 2 s 2 z 2 + 2 s t u v + 2 s t v z t 2 u 2 t 2 v 2 u 2 z 2 + 2 u v 2 z v 4
h 2 p q + h 2 s t + h 2 u v + h 2 v z h l n q h l q r h l q u h l q z h m n p h m p r h m p u h m q v i l n t + i l o q i m n s + i m o p l 2 n v + l 2 p q + l m n 2 + 2 l m n r + l m n u l m o 2 + l m q 2 + n 2 s t + n 2 u v + n 2 v z n o p t n o q s n p 2 v n p q u n p q z n q 2 v + o 2 p q + o 2 u v + o 2 v z 2 o p t u 2 o q t v + p 3 q p 2 r v + 2 p 2 s t + p 2 v z + p q 3 + p q r u p q r z p q s 2 + p q t 2 p q u z p q v 2 + q 2 r v + q 2 u v
h 2 q 2 + h 2 t 2 + h 2 v 2 + h 2 z 2 2 h m n q 2 h m q r 2 h m q u 2 h m q z 2 i m n t + 2 i m o q 2 l m n v + 2 l m p q + m 2 n 2 + 2 m 2 n r + 2 m 2 n u m 2 o 2 m 2 p 2 + m 2 q 2 + n 2 t 2 + n 2 v 2 + n 2 z 2 2 n o q t 2 n p q v 2 n q 2 z + o 2 q 2 + o 2 v 2 + o 2 z 2 2 o p t v 2 o q t z + p 2 q 2 + p 2 t 2 + p 2 z 2 2 p q v z + q 4 + q 2 t 2 + q 2 v 2
h i o p + h i r s + h i s u + h i t v h l o 2 h l r 2 h l s 2 h l t 2 i 2 n p i 2 o s i 2 p u i 2 q v + i l n o + i l o r + i l p s + i l q t + n o r s + n o s u + n o t v n p r 2 n p s 2 n p t 2 o 3 s + o 2 p r o 2 p u o 2 q v + o p 2 s + o p q t + o r s u + o r t v o s 3 o s t 2 p r 2 u + p r s 2 + p s t v p t 2 u q r 2 v + q r s t q s 2 v + q s t u
h i o q + h i r t + h i t u + h i t z h m o 2 h m r 2 h m s 2 h m t 2 i 2 n q i 2 o t i 2 q u i 2 q z + i m n o + i m o r + i m p s + i m q t l 2 o t + l 2 q r + l m o s l m p r + n o r t + n o t u + n o t z n q r 2 n q s 2 n q t 2 o 3 t + o 2 q r o 2 q u o 2 q z o p 2 t + 2 o p q s + o q 2 t + o r t u + o r t z o s 2 t o t 3 + p s t z p t 2 v q r 2 u q r 2 z + q r s 2 + q r t 2 q s 2 z + q s t v
h i p 2 + h i s 2 + h i u 2 + h i v 2 h l o p h l r s h l s u h l t v i l n p i l o s i l p u i l q v + l 2 n o + l 2 o r + l 2 p s + l 2 q t + n o s 2 + n o u 2 + n o v 2 n p r s n p s u n p t v o 2 p s + o p 2 r o p 2 u o p q v + o r u 2 + o r v 2 o s 2 u o t 2 u + p 3 s + p 2 q t p r s u p r t v + p s 3 + p s t 2 + p s v 2 p t u v q r s v + q r t u q s u v + q t u 2
h i p q + h i s t + h i u v + h i v z h m o p h m r s h m s u h m t v i l n q i l o t i l q u i l q z l 2 o v + l 2 q s + l m n o + l m o r + l m o u + l m q t + n o s t + n o u v + n o v z n q r s n q s u n q t v o 2 p t o p 2 v + o p q r o p q z + o r u v + o r v z o s t u o t 2 v + p 2 q s + p q 2 t p r s v + p s 2 t + p s v z p t v 2 q r s z + q s t 2 q s u z + q t u v
h i q 2 + h i t 2 + h i v 2 + h i z 2 h m o q h m r t h m t u h m t z i m n q i m o t i m q u i m q z 2 l m o v + l m p t + l m q s + m 2 n o + m 2 o r + 2 m 2 o u m 2 p s + m 2 q t + n o t 2 + n o v 2 + n o z 2 n q r t n q t u n q t z o 2 q t 2 o p q v + o q 2 r + o q 2 u o q 2 z + o r v 2 + o r z 2 o t 2 u o t 2 z + p 2 q t 2 p r t v + 2 p s t 2 + p s z 2 p t v z + q 3 t + q r t u q r t z q s 2 t q s v z + q t 3 + q t v 2
h l o q + h l r t + h l t u + h l t z h m o p h m r s h m s u h m t v i l n q i l o t i l q u i l q z + i m n p + i m o s + i m p u + i m q v l 2 p t + l 2 q s + n p r t + n p t u + n p t z n q r s n q s u n q t v o 2 p t + o 2 q s o p q z + o q 2 v p 3 t + p 2 q s + p r t u + p r t z p s 2 t p t 3 + p t u z p t v 2 q r s u q r s z + q s 3 + q s t 2 q s u z + q s v 2
h l p q + h l s t + h l u v + h l v z h m p 2 h m s 2 h m u 2 h m v 2 l 2 n q l 2 o t l 2 p v l 2 q z + l m n p + l m o s + l m p u + l m q v + n p s t + n p u v + n p v z n q s 2 n q u 2 n q v 2 o p 2 t + o p q s p 3 v + p 2 q u p 2 q z + p q 2 v + p r u v + p r v z p s 2 v p t 2 v + p u v z p v 3 q r u 2 q r v 2 + q s 2 u q s 2 z + 2 q s t v q u 2 z + q u v 2
h l q 2 + h l t 2 + h l v 2 + h l z 2 h m p q h m s t h m u v h m v z l m n q l m o t l m p v l m q z + m 2 n p + m 2 o s + m 2 p u + m 2 q v + n p t 2 + n p v 2 + n p z 2 n q s t n q u v n q v z o p q t + o q 2 s p 2 q v + p q 2 u p q 2 z + p r v 2 + p r z 2 2 p s t v + p t 2 u p t 2 z + p u z 2 p v 2 z + q 3 v q r u v q r v z + q s 2 v + q t 2 v q u v z + q v 3
h o s h p r i n s + i o p + l n r l o 2
h o t h q r i n t + i o q + m n r m o 2
h o u h p s i n u + i p 2 + l n s l o p
h o v h q s i n v + i p q + m n s m o p
h o z h q t i n z + i q 2 + m n t m o q
h p t h q s l n t + l o q + m n s m o p
h p v h q u l n v + l p q + m n u m p 2
h p z h q v l n z + l q 2 + m n v m p q
h r u h s 2 i o u + i p s + l o s l p r
h r v h s t i o v + i q s + l o t l q r
h r z h t 2 i o z + i q t + m o t m q r
h s v h t u l o v + l p t + m o u m p s
h s z h t v l o z + l q t + m o v m q s
h u z h v 2 l p z + l q v + m p v m q u

G i = G 24 i 2 p 2 + i 2 s 2 + i 2 u 2 + i 2 v 2 2 i l o p 2 i l r s 2 i l s u 2 i l t v + l 2 o 2 + l 2 r 2 + l 2 s 2 + l 2 t 2 + o 2 s 2 + o 2 u 2 + o 2 v 2 2 o p r s 2 o p s u 2 o p t v + p 2 r 2 + p 2 s 2 + p 2 t 2 + r 2 u 2 + r 2 v 2 2 r s 2 u 2 r s t v + s 4 + s 2 t 2 + s 2 v 2 2 s t u v + t 2 u 2
i 2 p q + i 2 s t + i 2 u v + i 2 v z i l o q i l r t i l t u i l t z i m o p i m r s i m s u i m t v l 2 r v + l 2 s t + l m o 2 + l m r 2 + l m r u + l m t 2 + o 2 s t + o 2 u v + o 2 v z o p r t o p t u o p t z o q r s o q s u o q t v p 2 r v + p 2 s t + p q r 2 + p q r u + p q t 2 + r 2 u v + r 2 v z r s 2 v r s t u r s t z r t 2 v + s 3 t + s 2 v z + s t 3 s t u z s t v 2 + t 2 u v
i 2 q 2 + i 2 t 2 + i 2 v 2 + i 2 z 2 2 i m o q 2 i m r t 2 i m t u 2 i m t z 2 l m r v + 2 l m s t + m 2 o 2 + m 2 r 2 + 2 m 2 r u m 2 s 2 + m 2 t 2 + o 2 t 2 + o 2 v 2 + o 2 z 2 2 o q r t 2 o q t u 2 o q t z 2 p q r v + 2 p q s t + q 2 r 2 + 2 q 2 r u q 2 s 2 + q 2 t 2 + r 2 v 2 + r 2 z 2 2 r s t v 2 r t 2 z + s 2 t 2 + s 2 z 2 2 s t v z + t 4 + t 2 v 2
i l p q + i l s t + i l u v + i l v z i m p 2 i m s 2 i m u 2 i m v 2 l 2 o q l 2 r t l 2 s v l 2 t z + l m o p + l m r s + l m s u + l m t v + o p s t + o p u v + o p v z o q s 2 o q u 2 o q v 2 p 2 r t p 2 s v p 2 t z + p q r s + p q s u + p q t v + r s u v + r s v z r t u 2 r t v 2 s 3 v + s 2 t u s 2 t z + s t 2 v + s u v z s v 3 t u 2 z + t u v 2
i l q 2 + i l t 2 + i l v 2 + i l z 2 i m p q i m s t i m u v i m v z l m o q l m r t l m s v l m t z + m 2 o p + m 2 r s + m 2 s u + m 2 t v + o p t 2 + o p v 2 + o p z 2 o q s t o q u v o q v z p q r t p q s v p q t z + q 2 r s + q 2 s u + q 2 t v + r s v 2 + r s z 2 r t u v r t v z s 2 t v + s t 2 u s t 2 z + s u z 2 s v 2 z + t 3 v t u v z + t v 3
i p t i q s l o t + l q r + m o s m p r
i p v i q u l o v + l q s + m o u m p s
i p z i q v l o z + l q t + m o v m p t
i s v i t u l r v + l s t + m r u m s 2
i s z i t v l r z + l t 2 + m r v m s t
i u z i v 2 l s z + l t v + m s v m t u

G 25 = G l l 2 q 2 + l 2 t 2 + l 2 v 2 + l 2 z 2 2 l m p q 2 l m s t 2 l m u v 2 l m v z + m 2 p 2 + m 2 s 2 + m 2 u 2 + m 2 v 2 + p 2 t 2 + p 2 v 2 + p 2 z 2 2 p q s t 2 p q u v 2 p q v z + q 2 s 2 + q 2 u 2 + q 2 v 2 + s 2 v 2 + s 2 z 2 2 s t u v 2 s t v z + t 2 u 2 + t 2 v 2 + u 2 z 2 2 u v 2 z + v 4

G 33 = G n n r u n s 2 o 2 u + 2 o p s p 2 r
n r v n s t o 2 v + o p t + o q s p q r
n r z n t 2 o 2 z + 2 o q t q 2 r
n s v n t u o p v + o q u + p 2 t p q s
n s z n t v o p z + o q v + p q t q 2 s
n u z n v 2 p 2 z + 2 p q v q 2 u

G 34 = G o o s v o t u p r v + p s t + q r u q s 2
o s z o t v p r z + p t 2 + q r v q s t
o u z o v 2 p s z + p t v + q s v q t u

G 44 = G r r u z r v 2 s 2 z + 2 s t v t 2 u

B Code for Chapter 2

The following script can be run in SageMath [52] and produces the Gröbner basis above together with the computations needed in the proof of Proposition 2.6. One can slightly modify the matrix in the beginning to adapt the code to higher dimension 𝑛. We caution the reader that the function for computing the set of unlucky primes, in the sense of Proposition 2.13, is highly inefficient. Especially, the last part of this code requires about one day running time on a laptop.

C Code for Chapter 7

The following script can be run in SageMath [52] and produces the list of admissible elements for the group-theoretical datum ( B C 3 , J = { 0 , 1 , 2 } , σ , ω 2 ) studied in Section 7.2. The function newtonPoint also computes the Newton point of a given element in the extended affine Weyl group.

Acknowledgements

First and foremost, I would like to thank my supervisor Eva Viehmann for her support during my PhD. I am sincerely thankful for her constant help and feedback, which guided me through my studies. I wish to express my gratitude to Michael Rapoport and Torsten Wedhorn for very helpful discussions and for answering my questions on their papers [41, 48]. I am thankful to Felix Schremmer for sharing his knowledge on Coxeter groups and affine Deligne–Lusztig varieties, pointing me to the relevant literature for Section 4. I would like to thank Simone Ramello for introducing me to model theory and working out together the details of Remark 2.16. I am also grateful to Urs Hartl and Damien Junger for helpful conversations.

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Received: 2023-11-06
Revised: 2025-06-14
Published Online: 2025-07-11
Published in Print: 2025-09-01

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