Worldsheet Dynamics of String Junctions

TL;DR

This work analyzes the worldsheet dynamics of string junctions in type IIB string theory, deriving the low-energy S-matrices that diagonalize into Dirichlet or Neumann boundary conditions for orthogonal combinations of string modes. It shows that the associated worldsheet theory for general BPS string networks preserves eight supercharges and constructs the band structure of simple string lattices, revealing how translational zero modes arise and how conformal-like behavior is generally not obtained at junctions. The results provide a concrete, solvable framework for understanding excitations on string networks and lattices, with implications for non-perturbative dynamics and potential compactification schemes. They also clarify how SL(2,ℤ) duality is reflected in the junction scattering and how the spectrum reorganizes in periodic lattices under various geometric and tension configurations.

Abstract

We analyze scattering of string modes at string junctions of type IIB string theory. In the infrared limit, certain orthogonal linear combinations of the fields on the different strings satisfy either Dirichlet or Neumann boundary conditions. We confirm that the worldsheet theory of a general string network has eight conserved supercharges in agreement with target space BPS considerations. As an application, we obtain the band spectrum of some simple string lattices.