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

The low-energy D = 4, N = 1 effective action of the strongly coupled heterotic string is explicitly computed by compactifying the Hořava-Witten theory on the deformed Calabi-Yau three-fold solution due to Witten. It is shown that, to order κ23, the Kähler potential is identical to that of the weakly coupled theory. Furthermore, the gauge kinetic functions are directly computed to order κ43 and shown to receive a non-vanishing correction. Also, we compute gauge matter terms in the Kahler potential to the order κ43 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.