Abstract:
We introduce a method of using the a dual type IIA string
to compute alpha'-corrections to the moduli space of
heterotic string compactifications. In particular we study
the hypermultiplet moduli space of a heterotic string on a
K3 surface. One application of this machinery shows that
type IIB strings compactified on a Calabi-Yau space suffer
from worldsheet instantons, spacetime instantons and, in
addition, "mixed" instantons which in a sense are both
worldsheet and spacetime. As another application we look at
the hyperkaehler limit of the moduli space in which the K3
surface becomes an ALE space. This is a variant of
the "geometric engineering" method used for vector
multiplet moduli space and should be applicable to a wide
range of examples. In particular we reproduce Sen and
Witten's result for the heterotic string on an A1
singularity and a trivial bundle and generalize this to a
collection of E8 point-like instantons on an ALE space.