Contents

spin geometry

string geometry

group theory

# Contents

## Idea

The semi-spin group in dimension 32.

## Properties

### In heterotic string theory

In heterotic string theory precisely two (isomorphism classes of) gauge groups are consistent (give quantum anomaly cancellation): one is the direct product group $E_8 \times E_8$ of the exceptional Lie group E8 with itself, the other is in fact the semi-spin group $SemiSpin(32)$ (see McInnes 99a, p. 5).

Beware that the string theory literature often writes this as Spin(32)$/\mathbb{Z}_2$, which is at best ambiguous and misleading, or even as SO(32), which is wrong. Of course this follows the general tradition in the physics literature to write identifications of Lie groups that are really only identifications of their Lie algebras, see also “SO(10)-GUT theory”.

sp. orth. groupspin grouppin groupsemi-spin group
SO(2)Spin(2)Pin(2)
SO(3)Spin(3)
SO(4)Spin(4)
SO(5)Spin(5)Pin(5)
Spin(6)
Spin(7)
SO(8)Spin(8)SO(8)
SO(9)Spin(9)
$\vdots$$\vdots$
SO(16)Spin(16)SemiSpin(16)
SO(32)Spin(32)SemiSpin(32)

see also

## References

Last revised on May 15, 2019 at 11:41:38. See the history of this page for a list of all contributions to it.