Super no-scale models in string theory

TL;DR

This paper explores super no-scale models in heterotic string theory, demonstrating their stability, suppressed vacuum energy, and dynamical Wilson line stabilization, leading to consistent low-energy theories with softly broken supersymmetry.

Contribution

It introduces a class of super no-scale heterotic string models with stable vacua, suppressed vacuum energy, and dynamical Wilson line stabilization, extending previous understanding of string supersymmetry breaking.

Findings

Vacuum energy exponentially suppressed at 1-loop level.

Models free of Hagedorn-like tachyonic singularities.

Wilson lines for asymptotically free groups stabilized dynamically.

Abstract

We consider "super no-scale models" in the framework of the heterotic string, where the N=4,2,1 --> 0 spontaneous breaking of supersymmetry is induced by geometrical fluxes realizing a stringy Scherk-Schwarz perturbative mechanism. Classically, these backgrounds are characterized by a boson/fermion degeneracy at the massless level, even if supersymmetry is broken. At the 1-loop level, the vacuum energy is exponentially suppressed, provided the supersymmetry breaking scale is small, m_{3/2} << M_{string}. We show that the "super no-scale string models" under consideration are free of Hagedorn-like tachyonic singularities, even when the supersymmetry breaking scale is large, m_{3/2} ~ M_{string}. The vacuum energy decreases monotonically and converges exponentially to zero, when m_{3/2} varies from M_{string} to 0. We also show that all Wilson lines associated to asymptotically free gauge symmetries are dynamically stabilized by the 1-loop effective potential, while those corresponding to non-asymtotically free gauge groups lead to instabilities and condense. The Wilson lines of the conformal gauge symmetries remain massless. When stable, the stringy super no-scale models admit low energy effective actions, where decoupling gravity yields theories in flat spacetime, with softly broken supersymmetry.