Atlas of Lie Groups and Representations

Tables · 2013

Galois cohomology of real groups

The tables gives |H1(Γ,G)| for every real form of a simple connected complex group, except for some intermediate covers in type A. Also the component groups of the adjoint groups are given. Here is some detail about the mathematics, the realex code used to produce the tables, and the output of the script (H1(Γ,G) for all simple, simply connected groups up to rank 8).

Please send comments and corrections to jda@math.umd.edu.

Simply Connected Classical groups
Group|H1(Γ,G)|
SL(n,R), GL(n,R), Sp(2n,R)1
SL(n,H), Spin*(2n)2
SU(p,q) ⌊p/2⌋ + ⌊q/2⌋+1
Sp(p,q)p+q+1
Spin(p,q) ⌊(p+q)/4⌋+δ(p,q)

In the last row δ(p,q) depends on p,q mod(4), according to the following table:

p\q0123
03222
12110
22110
32000
Simply Connected Exceptional groups
inner class group K real rank name |H1(Γ,G)|
compact E6 A5A1 4 quasisplit
quaternionic		 3
E6 D5T 2 Hermitian 3
E6 E6 0 compact 3
split E6 C4 6 split 2
E6 F4 2 quasicompact 2
compact E7 A7 7 split 2
E7 D6A1 4 quaternionic 4
E7 E6T 3 Hermitian 2
E7 E7 2 compact 4
compact E8 D8 8 split 3
E8 A7A1 4 quaternionic 3
E8 E8 0 compact 3
compact F4 C3A1 4 split 3
F4 B4 1 3
F4 F4 0 compact 3
compact G2 A1A1 2 split 2
G2 G2 0 compact 2
Special orthgonal groups
group|H1(Γ,G)|
SO(p,q)⌊p/2⌋+⌊q/2⌋+1
SO*(2n)2
Adjoint classical groups
group|π0(G(R))||H1(Γ,G)|
PSL(n,R)
2n even
1n odd
2n even
1n odd
PSL(n,H)12
PSU(p,q)
2p=q
1otherwise
⌊(p+q)/2⌋+1
PSO(p,q)
1pq=0
1p,q odd and p≠q
4p=q even
2otherwise
⌊(p+q+2)/4⌋p,q odd
⌊(p+q)/4⌋+3p,q even, p+q=0(4)
⌊(p+q)/4⌋+2p,q even, p+q=2(4)
(p+q+1)/2p,q opposite parity
PSO*(2n)
2n even
1n odd
n/2+3n even
(n-1)/2+2n odd
PSp(2n,R)2⌊n/2⌋+2
PSp(p,q)
2p=q
1otherwise
⌊(p+q)/2⌋+2

In types E8, F4 and G2 the adjoint group is simply connected. In simply connected type E6 the center has order 3, and the adjoint and simply connected groups have the same cohomology (and the real points are connected). The only essentially new adjoint case is E7.

Adjoint exceptional groups
groupKreal rankname|π0(G(R))| |H1(Γ,G)|
E7 A7 7 split 2 4
E7 D6A1 4 quaternionic 1 4
E7 E6T 3 Hermitian 2 4
E7 E7 0 compact 1 4

Page last changed on the old site: 2013-10-30