Non-Supersymmetric Open String Vacua

TL;DR

This paper reviews the construction of non-supersymmetric open string vacua, highlighting methods to achieve models with broken supersymmetry in the bulk but preserved on branes, and discusses conditions for vanishing cosmological constant.

Contribution

It introduces new constructions of non-supersymmetric open string vacua with controlled supersymmetry breaking and potential for zero cosmological constant using asymmetric orbifolds.

Findings

Supersymmetry remains unbroken on branes at all mass levels.

Bulk supersymmetry is broken but Fermi-Bose degeneracy is preserved perturbatively.

Certain Scherk-Schwarz compactifications can have vanishing cosmological constant.

Abstract

We review the construction of non-supersymmetric open string vacua in various dimensions. They can be obtained either projecting the (compactified) non-supersymmetric 0B theory, or applying the Scherk-Schwarz mechanism to open strings. Generically, these vacua generate a non-vanishing cosmological constant. However, one can construct particular kinds of Scherk-Schwarz compactifications with vanishing cosmological constant, at least for low orders, based on asymmetric orbifolds. A generic feature of these models is that supersymmetry remains unbroken on the branes at all mass level, while it is broken in the bulk in a way that preserves Fermi-Bose degeneracy at each mass level in the perturbative string spectrum.