To understand in detail duality between heterotic string and
F theory compactifications, it is important to understand the construction of holomorphic
G bundles over elliptic Calabi-Yau manifolds, for various groups
G. In this paper, we develop techniques to describe these bundles, and make several detailed comparisons between the heterotic
string and
F theory.
Received: 6 February 1997 / Accepted: 29 May 1997