Type $\mathbf{\bar{0}}$ Heterotic String Orbifolds

TL;DR

This paper introduces non-supersymmetric, tachyon-free type 0̄ heterotic string orbifolds with no massless twisted sector states, which could provide insights into early universe string dynamics.

Contribution

It demonstrates the existence of non-supersymmetric, tachyon-free type 0̄ Z2×Z2 heterotic string orbifolds with unique massless state properties.

Findings

Existence of tachyon-free, non-supersymmetric type 0̄ models.

Models have no massless twisted sector states.

Models exhibit a positive cosmological constant.

Abstract

The $Z_2\times Z_2$ heterotic string orbifold gives rise to a large space of phenomenological three generation models that serves as a testing ground to explore how the Standard Model of particle physics may be incorporated in a theory of quantum gravity. Recently, we demonstrated the existence of type 0 $Z_2\times Z_2$ heterotic string orbifolds in which there are no massless fermionic states. In this paper we demonstrate the existence of non--supersymmetric tachyon--free $Z_2\times Z_2$ heterotic string orbifolds that do not contain any massless bosonic states from the twisted sectors. We dub these configurations type ${\bar 0}$ models. They necessarily contain untwisted bosonic states, producing the gravitational, gauge and scalar moduli degrees of freedom, but possess an excess of massless fermionic states over bosonic ones, hence producing a positive cosmological constant. Such configurations may be instrumental when trying to understand the string dynamics in the early universe.