Free fermionic webs of heterotic T-folds

Moduli stabilisation is key to obtaining phenomenologically viable string models. Non-geometric compactifications, like T-duality orbifolds (T-folds), are capable of freezing many moduli. However, T-folds, admitting free fermionic descriptions, can be associated to a large number of different T-folds with varying number of moduli, since the fermion pairings for bosonisation is far from unique. Fermion symmetries induce mappings in the bosonised description that extend the T-duality group.