Aspinwall, PS; Morrison, DR, *U-duality and integral structures*,
Physics Letters B, vol. 355 no. 1-2
(1995),
pp. 141-149 [doi] .
**Abstract:**

*We analyze the U-duality group of the case of a type II superstring compactified to four dimensions on a K3 surface times a torus. The various limits of this theory are considered which have interpretations as type IIA and IIB superstrings, the heterotic string, and eleven-dimensional supergravity, allowing all these theories to be directly related to each other. The integral structure which appears in the Ramond-Ramond sector of the type II superstring is related to the quantum cohomology of general Calabi-Yau threefolds which allows the moduli space of type II superstring compactifications on Calabi-Yau manifolds to be analyzed. © 1995.*