4-string Junction and Its Network

TL;DR

This paper investigates a four-string junction in supergravity, demonstrating charge conservation, force balance, and supersymmetry preservation, and constructs a network of such junctions as stable BPS configurations.

Contribution

It introduces a detailed analysis of 4-string junctions in supergravity, establishing their force balance and supersymmetry properties, and constructs complex string networks from these junctions.

Findings

Charge conservation implies force balance at the junction.

A 4-string junction preserves 1/8 of supersymmetry.

Constructed a supersymmetric string network from 4-string junctions.

Abstract

We study a BPS configuration in which four strings (of different type) meet at a point in $N = 2, D = 8$ supergravity, i.e., the low energy effective theory of $T^2$-compactified type II string theory. We demonstrate that the charge conservation of the four strings implies the vanishing of the net force (due to the tensions of various strings) at the junction and vice versa, using the tension formula for $SL(3, Z)$ strings obtained recently by the present authors. We then show that a general 4-string junction preserves 1/8 of the spacetime supersymmetries. Using 4-string junctions as building blocks, we construct a string network which also preserves 1/8 of the spacetime supersymmetries.