Aspects of bosonization in string theory

Non-supersymmetric string theories with world-sheet fermions are considered. Different consistent ways of summing over the spin structures lead to various vacua of the bosonic theory. In particular, fermionic models with O(2n) × O(2n) symmetry are equivalent to bosonic systems with non-zero constant torsion. Fermionic models with the non-simply laced symmetry groups O(2n - 1) × O(2n - 1) are bosonized to a string propagating on an orbifold.