Open-string models with broken supersymmetry

TL;DR

This paper reviews three classes of open-string models with broken supersymmetry, illustrating phenomena like brane supersymmetry and its breaking, and discusses their implications for string vacua construction.

Contribution

It categorizes and analyzes three distinct classes of open-string models with broken supersymmetry, highlighting their unique features and implications.

Findings

Supersymmetry is broken in both sectors in the first class.

In the second class, supersymmetry is broken in the closed sector but preserved in the open sector.

Brane supersymmetry breaking offers solutions to longstanding issues in open-string vacua.

Abstract

I review the salient features of three classes of open-string models with broken supersymmetry. These suffice to exhibit, in relatively simple settings, the two phenomena of ``brane supersymmetry'' and ``brane supersymmetry breaking''. In the first class of models, to lowest order supersymmetry is broken both in the closed and in the open sectors. In the second class of models, to lowest order supersymmetry is broken in the closed sector, but is {\it exact} in the open sector, at least for the low-lying modes, and often for entire towers of string excitations. Finally, in the third class of models, to lowest order supersymmetry is {\it exact} in the closed (bulk) sector, but is broken in the open sector. Brane supersymmetry breaking provides a natural solution to some old difficulties met in the construction of open-string vacua.