The Non-Perturbative SO(32) Heterotic String

TL;DR

This paper explores the non-perturbative aspects of the SO(32) heterotic string, revealing how it can be derived from type IIB string theory through discrete symmetry gauging and analyzing the role of D-strings and NS 9-branes at various coupling regimes.

Contribution

It demonstrates a non-perturbative construction of the SO(32) heterotic string from type IIB string theory, highlighting the role of D-strings and NS 9-branes at finite and zero coupling.

Findings

SO(32) heterotic string obtained from type IIB via discrete symmetry gauging

Finite coupling involves SO(32) charges tethered by open D-strings

Zero coupling limit reproduces standard heterotic world-sheet currents

Abstract

The SO(32) heterotic string can be obtained from the type IIB string by gauging a discrete symmetry that acts as $(-1)^{F_L}$ on the perturbative string states and reverses the parity of the D-string. Consistency requires the presence of 32 NS 9-branes -- the S-duals of D9-branes -- which give SO(32) Chan-Paton factors to open D-strings. At finite string coupling, there are SO(32) charges tethered to the heterotic string world-sheet by open D-strings. At zero-coupling, the D-string tension becomes infinite and the SO(32) charges are pulled onto the world-sheet, and give the usual SO(32) world-sheet currents of the heterotic string.