BPS NATURE OF 3-STRING JUNCTIONS

We study BPS-saturated classical solutions for the world-sheet theory of a D-string in the presence of a point charge. These solutions are i nterpreted as describing planar 3-string junctions, which arise becaus e the original D-string is deformed by the presence of the inserted ch arge. We compute the angles of the junctions and show that the Vector sum of string tensions is zero, confirming a conjecture of Schwarz tha t such configurations are BPS states. (C) 1998 Published by Elsevier S cience B.V.