Heterotic String

A new type of superstring theory is constructed as a chiral combination of the closed $D=26\mathrm{}$ bosonic and $D=10\mathrm{}$ fermionic strings. The theory is supersymmetric, Lorentz invariant, and free of tachyons. Consistency requires the gauge group to be $\frac{\mathrm{Spin}\mathrm{}\left(32\right)\mathrm{}}{Z_2}$ or $E_8\times E_8$.