On Non-tachyonic Z_N x Z_M Orientifolds of Type 0B String Theory

TL;DR

This paper investigates non-tachyonic orientifolds of type 0B string theory on Z_N x Z_M orbifolds, finding that only the Z_2 x Z_2 case can be made tachyon-free, with explicit open string amplitude constructions.

Contribution

It provides a comprehensive analysis showing that only the Z_2 x Z_2 orbifold yields a tachyon-free model, and explicitly constructs the open string amplitudes for this case.

Findings

Z_2 x Z_2 orbifold is unique in being tachyon-free

Explicit open string amplitudes are constructed for Z_2 x Z_2

Gauge groups are symplectic or unitary depending on projections

Abstract

We study open descendants of four dimensional Z_N x Z_M orbifolds of the non-supersymmetric type 0B string theory. An exhaustive analysis shows, that using the crosscap constraint the only model for which one can project out the tachyon is the Z_2 x Z_2 orbifold. For this case we explicitly construct the open string amplitudes. The gauge group corresponding to the various inequivalent Klein bottle projections turns out to be either symplectic or unitary.