STRONG-COUPLING EXPANSION OF CALABI-YAU COMPACTIFICATION

In a certain strong coupling limit, compactification of the E(8) x E(8 ) heterotic string on a Calabi-Yau manifold X can be described by an e leven-dimensional theory compactified on X x S-1/Z(2). In this limit, the usual relations among low-energy gauge couplings hold, but the usu al (problematic) prediction for Newton's constant does not. In this pa per, the equations for unbroken supersymmetry are expanded to the firs t non-trivial order, near this limit, verifying the consistency of the description and showing how, in some cases, if one tries to make Newt on's constant too small, strong coupling develops in one of the two E( 8)'s. The lower bound on Newton's constant (beyond which strong coupli ng develops) is estimated and is relatively close to the actual value.