M12 Modulo 5
The Hecke algebra for the Mathieu Group M12 with point
stabilizer being the normalizer of a
Sylow 5-subgroup
in characteristic 5
.
The Module M
The module M is the permutation module over the
field of chacteristic 5, having point stablilizer
of order 40
. The dimension of M is 2376
.
The dimensions of the irreducible submodules modules are
120,
98,
78,
66,
55,
55,
55,
45,
16,
16,
11,
11,
1
.
The module M has radical filtration (Loewy series)
1,
1,
2,
2,
3,
3,
4,
4,
5,
6,
7,
8,
8,
9,
10,
11,
12,
13
2,
2,
3,
3,
3,
3,
4,
4,
9,
10,
11,
12,
13,
13
2,
2,
3,
3,
4,
4,
9,
10,
11,
12
9,
10,
11,
12
9,
10,
11,
12
The module M has socle filtration (socle series)
9,
10,
11,
12
9,
10,
11,
12
2,
2,
3,
3,
4,
4,
9,
10,
11,
12
2,
2,
3,
3,
3,
3,
4,
4,
9,
10,
11,
12,
13,
13
1,
1,
2,
2,
3,
3,
4,
4,
5,
6,
7,
8,
8,
9,
10,
11,
12,
13
The module M has simple direct summands:
2 copies of simple module number 1
1 copy of simple module number 5
1 copy of simple module number 6
1 copy of simple module number 7
2 copies of simple module number 8
1 copy of simple module number 13
The remaining indecomposable components of M
have radical and socle filtrations as follows:
1).
radical layers
4
3
4
socle layers
4
3
4
2).
radical layers
4
3
4
socle layers
4
3
4
3).
radical layers
2
3,
13
2
socle layers
2
3,
13
2
4).
radical layers
3
2,
4
3
socle layers
3
2,
4
3
5).
radical layers
3
2,
4
3
socle layers
3
2,
4
3
6).
radical layers
2
3,
13
2
socle layers
2
3,
13
2
7).
radical layers
10
11
9
12
10
socle layers
10
11
9
12
10
8).
radical layers
12
10
11
9
12
socle layers
12
10
11
9
12
9).
radical layers
9
12
10
11
9
socle layers
9
12
10
11
9
10).
radical layers
11
9
12
10
11
socle layers
11
9
12
10
11
The Action Algebra
The action algebra A is the image of kG in the
k-endomorphism ring of M. It's simple modules are the irreducible
submodules of M.
The dimensions of the projective modules are
120,
275,
320,
210,
55,
55,
55,
45,
70,
70,
65,
65,
99
.
The cartan matrix of A is
1,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0
0,
2,
1,
0,
0,
0,
0,
0,
0,
0,
0,
0,
1
0,
1,
2,
1,
0,
0,
0,
0,
0,
0,
0,
0,
0
0,
0,
1,
2,
0,
0,
0,
0,
0,
0,
0,
0,
0
0,
0,
0,
0,
1,
0,
0,
0,
0,
0,
0,
0,
0
0,
0,
0,
0,
0,
1,
0,
0,
0,
0,
0,
0,
0
0,
0,
0,
0,
0,
0,
1,
0,
0,
0,
0,
0,
0
0,
0,
0,
0,
0,
0,
0,
1,
0,
0,
0,
0,
0
0,
0,
0,
0,
0,
0,
0,
0,
2,
1,
1,
1,
0
0,
0,
0,
0,
0,
0,
0,
0,
1,
2,
1,
1,
0
0,
0,
0,
0,
0,
0,
0,
0,
1,
1,
2,
1,
0
0,
0,
0,
0,
0,
0,
0,
0,
1,
1,
1,
2,
0
0,
1,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
1
The determinant of the Cartan matrix is 5.
The blocks of A consist of the following irreducible
modules:
(1).
1
(2).
2,
3,
4,
13
(3).
5
(4).
6
(5).
7
(6).
8
(7).
9,
10,
11,
12
Projective modules number
1,
5,
6,
7,
8
are simple.
The radical and socle filtrations of the remaining
projective modules for A are the following:
Projective module number 2
radical layers
2
3,
13
2
socle layers
2
3,
13
2
Projective module number 3
radical layers
3
2,
4
3
socle layers
3
2,
4
3
Projective module number 4
radical layers
4
3
4
socle layers
4
3
4
Projective module number 9
radical layers
9
12
10
11
9
socle layers
9
12
10
11
9
Projective module number 10
radical layers
10
11
9
12
10
socle layers
10
11
9
12
10
Projective module number 11
radical layers
11
9
12
10
11
socle layers
11
9
12
10
11
Projective module number 12
radical layers
12
10
11
9
12
socle layers
12
10
11
9
12
Projective module number 13
radical layers
13
2
socle layers
13
2
The degrees of the splitting fields are
1,
1,
1,
1,
1,
1,
1,
1,
1,
1,
1,
1,
1
.
The Hecke Algebra
The Hecke algebra H of the module M is the A-endomorphism
ring of M.
The dimension of H is
72
.
The dimensions of the irreducible H-modules are
2,
2,
2,
2,
2,
1,
1,
1,
1,
1,
1,
1,
1
.
The degrees of the splitting fields are
1,
1,
1,
1,
1,
1,
1,
1,
1,
1,
1,
1,
1
.
The dimensions of the projective modules of H are
2,
6,
8,
2,
6,
1,
1,
1,
1,
5,
5,
5,
5
.
The cartan matrix of H is
1,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0
0,
2,
1,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0
0,
1,
2,
0,
1,
0,
0,
0,
0,
0,
0,
0,
0
0,
0,
0,
1,
0,
0,
0,
0,
0,
0,
0,
0,
0
0,
0,
1,
0,
2,
0,
0,
0,
0,
0,
0,
0,
0
0,
0,
0,
0,
0,
1,
0,
0,
0,
0,
0,
0,
0
0,
0,
0,
0,
0,
0,
1,
0,
0,
0,
0,
0,
0
0,
0,
0,
0,
0,
0,
0,
1,
0,
0,
0,
0,
0
0,
0,
0,
0,
0,
0,
0,
0,
1,
0,
0,
0,
0
0,
0,
0,
0,
0,
0,
0,
0,
0,
2,
1,
1,
1
0,
0,
0,
0,
0,
0,
0,
0,
0,
1,
2,
1,
1
0,
0,
0,
0,
0,
0,
0,
0,
0,
1,
1,
2,
1
0,
0,
0,
0,
0,
0,
0,
0,
0,
1,
1,
1,
2
The determinant of the Cartan matrix is 20.
The blocks of H consist of the following irreducible
modules:
(1).
1
(2).
2,
3,
5
(3).
4
(4).
6
(5).
7
(6).
8
(7).
9
(8).
10,
11,
12,
13
Projective modules number
1,
4,
6,
7,
8,
9
are simple.
The radical and socle filtrations of the remaining
projective modules for H are the following:
Projective module number 2
radical layers
2
3
2
socle layers
2
3
2
Projective module number 3
radical layers
3
2,
5
3
socle layers
3
2,
5
3
Projective module number 5
radical layers
5
3
5
socle layers
5
3
5
Projective module number 10
radical layers
10
11
12
13
10
socle layers
10
11
12
13
10
Projective module number 11
radical layers
11
12
13
10
11
socle layers
11
12
13
10
11
Projective module number 12
radical layers
12
13
10
11
12
socle layers
12
13
10
11
12
Projective module number 13
radical layers
13
10
11
12
13
socle layers
13
10
11
12
13