Multicharge Superstrings

There are an infinite number of type IIB superstrings in ten dimensions, called (p,q) strings, that are labeled by two distinct string charges. They can form string junctions and string networks. These are the key to understanding the Coulomb branch BPS spectrum of N=4 super Yang--Mills theories in four dimensions. Nongravitational theories that are analogous to type IIB superstring theory in some respects are the ADE (2,0) six-dimensional theories on the Coulomb branch. Each of them contains a finite number of half-BPS superstrings, which can be labeled by the root vectors of the Lie algebra. When the rank is greater than one, these strings can also form string junctions and string networks. The relationship between N=4 super Yang--Mills theories in four dimensions and the (2,0) theories in six dimensions can be explored by utilizing the duality between type IIB superstring theory compactified on a circle and M-theory compactified on a torus.