On the four-dimensional effective action of strongly coupled heterotic string theory

The low-energy D = 4, N = 1 effective action of the strongly coupled heterotic string is explicitly computed by compactifying the Horava-Witten theory on the deformed Calabi-Yau three-fold solution due to Witten. It is shown that, to order kappa(2/3), the Kahler potential is identical to that of the weakly coupled theory. Furthermore, the gauge kinetic functions are directly computed to order kappa(4/3) and shown to receive a non-vanishing correction. Also, we compute gauge matter terms in the Kahler potential to the order kappa(4/3) and find a non-trivial correction to the dilaton term. Part of those corrections arise from background fields that depend on the orbifold coordinate and are excited by four-dimensional gauge field source terms. (C) 1998 Elsevier Science B.V.