Classification of the N = 2, Z2 × Z2-symmetric type II orbifolds and their type II asymmetric duals Original Research Article

Using free world-sheet fermions, we construct and classify all the N = 2, Z2 × Z2 four-dimensional orbifolds of the type IIA/B strings for which the orbifold projections act symmetrically on the left- and right-movers. We study the deformations of these models out of the fermionic point, deriving the partition functions at a generic point in the moduli of the internal tours T6 = T2 × T2 × T2. We investigate some of their perturbative and non-perturbative dualities and construct new dual pairs of type IIA/type II asymmetric orbifolds, which are related non-perturbatively and allow us to gain insight into some of the non-perturbative properties of the type IIA/B strings in four dimensions. In particular, we consider some of the (non)-perturbative gravitational corrections.