I was wondering with the SO(32) (i think it is) for the heterotic string theory/model. Is that the resultant of 2 different string theories/models, in terms of the math or from 2 different string theory/model symmetries..

Edited September 25, 201015 yr by beyond...

In string theory "left-movers" and "right-movers" do not talk to each other, so it is possible to construct a hybrid theory in which the "left-movers" are from the bosonic 26d string and the "right-movers" are from the 10d superstring.

 

If I recall, compactification of 26d to 10 and cancellation of anomalies means we have [math]SO(32)[/math] and [math] E_{8}\times E_{8}[/math] as the only possible gauge groups. The theory is self-consistent, ghost-free, anomaly-free and one-loop finite.

 

In the low energy limit we have a 10d supergravity theory coupled to supersymmetric Yang-Mills theory. There is "enough room" here to include the standard model and hence the interest in this string theory.