# Questions about Type HE Matrix String Theory

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I was reading the heterotic string section of this thesis desertation by Luboš Motl, since I think I now understand the Type IIA Matrix String Theory. The only thing I knew about Type HE Matrix Strings, however, was:

That It has a gauge-group of $O(N)$.

From the paper, I can see that the Type HE Matrix Strings, in order to be consistent, need some sort of "extra terms" (wrt the BFSS Lagrangian Density/SuperYM Lagrangian Density ) in order to exist in 11-Dimensional spacetime.

Now,

• What is the intuition behind this; intuitively, why does the absence of these "extra terms" cause such problems in 11-Dimensional spacetime. Given the amount of intuition behind Type IIA Matrix Strings, I expect that there may be some intuition in Type HE Matrix Strings too ?

• Where does the new gauge group of $O(N)$ come from when the gauge group of BFSS itself, was $U(N)$ all along.

@LubošMotl: Actually, my question is mainly about the intuition; i.e., is there a similar, elegant intuition for Type HE matrix strings, as there is for the Type IIA? About the infinite $N$ being finite $N$ being related to the momentum being non - zero and finite, etc.
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