BPS Dynamics of (p,q) Triple String Junction

We study dynamics of triple junction of $(p,q)$ strings in Type IIB string theory. We probe tension and mass density of $(p,q)$ strings by studying harmonic fluctuations of the triple junction. We show that they agree perfectly with BPS formula provided suitable geometric interpretation of the junction is given. At weak coupling and sufficiently dense limit, we argue that network of $(p,q)$ string becomes a `wiggly string', whose low-energy dynamics can be described via renormalization group evolved, smooth effective string. We also suggest the possibility that, upon Type IIB string is promoted to M-theory membrane, there can exist `evanescent' bound-states localized at triple junction.