Non-BPS states and heterotic – type I ′ duality

Abstract

There are two families of non-BPS bi-spinors in the perturbative spectrum of the nine-dimensional heterotic string charged under the gauge group SO(16)× SO(16). The relation between these perturbative non-BPS states and certain non-perturbative non-BPS D-brane states of the dual type I ′ theory is exhibited. The relevant branes include a Z 2 charged non-BPS D-string, and a bound state of such a D-string with a fundamental string. The domains of stability of these states as well as their decay products in both theories are determined and shown to agree with the duality map.