2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/55966We analyse the dipole solution of heterotic string theory in four dimensions. It has the structure of monopole and anti-monopole connected by flux line (string). Due to growing coupling near the poles, the length of the string diverges. However, exploiting the self-duality of heterotic string theory in four dimension, we argue that this string is correctly described in terms of dual variables.8 pages, harvmac, no figureHigh Energy Physics - Theorytext