A Non-Supersymmetric Open String Theory and S-Duality

TL;DR

The paper constructs a non-supersymmetric open string theory, Type O, as both an orbifold of Type I and an orientifold of Type B, with gauge group ${SO(32) imes SO(32)}$ and tachyonic excitations in both closed and open sectors. It analyzes the D-brane content and boundary states, showing how the Type O spectrum connects to doubled RR sectors and Omega-invariant branes, and identifies a striking match between one 1-brane’s worldsheet content and the $D=26$ bosonic string compactified on the ${SO(32)}$ lattice, which motivates a strong-coupling duality to that bosonic theory. This duality, if confirmed, would provide a rare example of non-supersymmetric string duality and challenge assumptions about tachyons and stability in non-supersymmetric settings. The work also introduces a boundary-state–based approach to D-brane analysis in non-supersymmetric theories and discusses broader interpretations in the context of F-theory/quotient constructions. Overall, the paper proposes a concrete, non-supersymmetric strong-coupling relation and lays groundwork for further understanding of tachyonic spectra and non-perturbative dynamics in such theories.

Abstract

A non-supersymmetric ten-dimensional open string theory is constructed as an orbifold of type I string theory, and as an orientifold of the bosonic type B theory. It is purely bosonic, and cancellation of massless tadpoles requires the gauge group to be SO(32)xSO(32). The spectrum of the theory contains a closed string tachyon, and open string tachyons in the (32,32) multiplet. The D-branes of this theory are analyzed, and it is found that the massless excitations of one of the 1-branes coincide with the world-sheet degrees of freedom of the D=26 bosonic string theory compactified on the SO(32) lattice. This suggests that the two theories are related by S-duality.