Stringy N = 1 super no-scale models

Abstract

N=1 no-scale models describe at tree level the spontaneous breaking of supersymmetry at an arbitrary scale m_{3/2}, with vanishing vacuum energy. We define N=1 super no-scale models in string theory as being those, which maintain these properties at 1-loop. In other words, in super no-scale models, m_{3/2} is a flat direction of a positive semi-definite 1-loop effective potential. We find explicit examples in heterotic Z_2 x Z_2 orbifold models, where N=1 is spontaneously broken by a stringy Scherk-Schwarz mechanism, and where the "decompactification problem" does not arise.