THE HETEROTIC STRING IS A SOLITON (VOL B458, PG 456, 1996)

It is shown that the Type IIA superstring compactified on K3 has a smo oth string soliton with the same zero mode structure as the heterotic string compactified on a four-torus, thus providing new evidence for a conjectured exact duality between the two six-dimensional string theo ries. The chiral worldsheet bosons arise as zero modes of Ramond-Ramon d fields of the IIA string theory and live on a signature (20, 4) even , self-dual lattice. Stable, finite loops of soliton string provide th e charged Ramond-Ramond states necessary for enhanced gauge symmetries at degeneration points of the K3 surface. It is also shown that Type IIB strings toroidally compactified to six dimensions have a multiplet of string solutions with Spe II worldsheets.