Matching the BPS Spectra of Heterotic - Type I - Type I' Strings

TL;DR

This paper explores the correspondence of BPS states across heterotic, type I, and type I' string theories in nine dimensions, highlighting how brane states induce gauge symmetry enhancements at specific moduli points.

Contribution

It provides a detailed analysis of BPS state matching and explicitly identifies brane states responsible for gauge symmetry enhancements in type I' theory.

Findings

Matching of BPS spectra across theories in 9D

Identification of brane states causing gauge enhancement

Explicit example of $SO(16)\times SO(16)$ to $E_8\times E_8$ transition

Abstract

We give a detailed discussion of the matching of the BPS states of heterotic, type I and type I' theories in d=9 for general backgrounds. This allows us to explicitly identify these (composite) brane states in the type I' theory that lead to gauge symmetry enhancement at critical points in moduli space. An example is the enhancement of $SO(16)\times SO(16)$ to $E_8\times E_8$.