String Junction from Worldsheet Gauge Theory
  We study the three-pronged strings (three string junctions) from the point of view of D-string worldsheet gauge theory. We justify interpreting kink solutions in the 2-dimensional gauge theory as pronged strings by examining BPS energy bounds obtained from this theory. When the ends of the pronged string are on D3-branes, the configuration preserves 1/4 supersymmetry with BPS conditions including the Nahm equation. Using solutions of the Nahm equation explicitly, we treat string junction configuration ending on the D3-branes from the viewpoint of the D-string. In particular, when two separated pronged strings end on the same D3-branes, they interact with each other through the D3-branes and the resultant trajectories of three-pronged strings are found to be curved non-trivially. 
Koji Hashimoto