Conway group Co3

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In the area of modern algebra known as group theory, the Conway group is a sporadic simple group of order

Contents

   495,766,656,000
= 210 ·37 ·53 ·7 ·11 ·23
≈ 5×1011.

History and properties

is one of the 26 sporadic groups and was discovered by John HortonConway  ( 1968 , 1969 ) as the group of automorphisms of the Leech lattice fixing a lattice vector of type 3, thus length 6. It is thus a subgroup of . It is isomorphic to a subgroup of . The direct product is maximal in .

The Schur multiplier and the outer automorphism group are both trivial.

Representations

Co3 acts on the unique 23-dimensional even lattice of determinant 4 with no roots, given by the orthogonal complement of a norm 4 vector of the Leech lattice. This gives 23-dimensional representations over any field; over fields of characteristic 2 or 3 this can be reduced to a 22-dimensional faithful representation.

Co3 has a doubly transitive permutation representation on 276 points.

WalterFeit  ( 1974 ) showed that if a finite group has an absolutely irreducible faithful rational representation of dimension 23 and has no subgroups of index 23 or 24 then it is contained in either or .

Maximal subgroups

Some maximal subgroups fix or reflect 2-dimensional sublattices of the Leech lattice. It is usual to define these planes by h-k-l triangles: triangles including the origin as a vertex, with edges (differences of vertices) being vectors of types h, k, and l.

LarryFinkelstein ( 1973 ) found the 14 conjugacy classes of maximal subgroups of as follows:

Maximal subgroups of Co3
No.StructureOrderIndexComments
1 McL:21,796,256,000
= 28·36·53·7·11
276
= 22·3·23
McL fixes a 2-2-3 triangle. The maximal subgroup also includes reflections of the triangle. has a doubly transitive permutation representation on 276 type 2-2-3 triangles having as an edge a type 3 vector fixed by .
2 HS 44,352,000
= 29·32·53·7·11
11,178
= 2·35·23
fixes a 2-3-3 triangle
3U4(3).2213,063,680
= 29·36·5·7
37,950
= 2·3·52·11·23
4 M23 10,200,960
= 27·32·5·7·11·23
48,600
= 23·35·52
fixes a 2-3-4 triangle
535:(2 × M11)3,849,120
= 25·37·5·11
128,800
= 25·52·7·23
fixes or reflects a 3-3-3 triangle
62·Sp6(2)2,903,040
= 210·34·5·7
170,775
= 33·52·11·23
centralizer of an involution of class 2A (trace 8), which moves 240 of the 276 type 2-2-3 triangles
7U3(5):S3756,000
= 25·33·53·7
655,776
= 25·34·11·23
831+4
+
:4S6
699,840
= 26·37·5
708,400
= 24·52·7·11·23
normalizer of a subgroup of order 3 (class 3A)
92A8322,560
= 210·32·5·7
1,536,975
= 35·52·11·23
10PSL(3,4):(2 × S3)241,920
= 28·33·5·7
2,049,300
= 22·34·52·11·23
112 × M12 190,080
= 27·33·5·11
2,608,200
= 23·34·52·7·23
centralizer of an involution of class 2B (trace 0), which moves 264 of the 276 type 2-2-3 triangles
12[210.33]27,648
= 210·33
17,931,375
= 34·53·7·11·23
13S3 × PSL(2,8):39,072
= 24·34·7
54,648,000
= 26·33·53·11·23
normalizer of a subgroup of order 3 (class 3C, trace 0)
14A4 × S51,440
= 25·32·5
344,282,400
= 25·35·52·7·11·23

Conjugacy classes

Traces of matrices in a standard 24-dimensional representation of Co3 are shown. [1] The names of conjugacy classes are taken from the Atlas of Finite Group Representations. [2] [3] The cycle structures listed act on the 276 2-2-3 triangles that share the fixed type 3 side. [4]

ClassOrder of centralizerSize of classTraceCycle type
1Aall Co3124
2A2,903,04033·52·11·238136,2120
2B190,08023·34·52·7·230112,2132
3A349,92025·52·7·11·23-316,390
3B29,16027·3·52·7·11·236115,387
3C4,53627·33·53·11·230392
4A23,0402·35·52·7·11·23-4116,210,460
4B1,5362·36·53·7·11·23418,214,460
5A150028·36·7·11·23-11,555
5B30028·36·5·7·11·23416,554
6A4,32025·34·52·7·11·23516,310,640
6B1,29626·33·53·7·11·23-123,312,639
6C21627·34·53·7·11·23213,26,311,638
6D10828·34·53·7·11·23013,26,33,642
6E7227·35·53·7·11·23034,644
7A4229·36·53·11·23313,739
8A19224·36·53·7·11·23212,23,47,830
8B19224·36·53·7·11·23-216,2,47,830
8C3225·37·53·7·11·23212,23,47,830
9A16229·33·53·7·11·23032,930
9B81210·33·53·7·11·23313,3,930
10A6028·36·52·7·11·2331,57,1024
10B2028·37·52·7·11·23012,22,52,1026
11A2229·37·53·7·2321,1125power equivalent
11B2229·37·53·7·2321,1125
12A14426·35·53·7·11·23-114,2,34,63,1220
12B4826·36·53·7·11·23112,22,32,64,1220
12C3628·35·53·7·11·2321,2,35,43,63,1219
14A1429·37·53·11·2311,2,751417
15A15210·36·52·7·11·2321,5,1518
15B3029·36·52·7·11·23132,53,1517
18A1829·35·53·7·11·2326,94,1813
20A2028·37·52·7·11·2311,53,102,2012power equivalent
20B2028·37·52·7·11·2311,53,102,2012
21A21210·36·53·11·2303,2113
22A2229·37·53·7·2301,11,2212power equivalent
22B2229·37·53·7·2301,11,2212
23A23210·37·53·7·1112312power equivalent
23B23210·37·53·7·1112312
24A2427·36·53·7·11·23-1124,6,1222410
24B2427·36·53·7·11·2312,32,4,122,2410
30A3029·36·52·7·11·2301,5,152,308

Generalized Monstrous Moonshine

In analogy to monstrous moonshine for the monster M, for Co3, the relevant McKay-Thompson series is where one can set the constant term a(0) = 24 ( OEIS:  A097340 ),

and η(τ) is the Dedekind eta function.

References

  1. Conway et al. (1985)
  2. "ATLAS: Conway group Co3".
  3. "ATLAS: Conway group Co1".
  4. "ATLAS: Co3 — Permutation representation on 276 points".