Supersymmetry restoration in the compactified O(16) ⊗ O (16)' heterotic string theory

String duality and nonsupersymmetric strings

“…This exponential suppression of Λ at large R in models with equal numbers of massless fermions and bosons and supersymmetry broken by twisted boundary conditions was noted previously in [14].…”

Dynamical supersymmetry breaking with a large internal dimension

“…In fact they are exponentially suppressed (up to constants) [4]. Moreover the radius dependence of the one-loop cosmological constant can be calculated with the result [13,4]: 9) where n B and n F are the number of massless bosons and fermions, respectively, after the supersymmetry breaking, and the ellipsis stands for corrections which are exponentially suppressed in terms of R 2 . The absence of 1/R 2 terms in (2.9) implies the vanishing of StrM 2 and, hence, of quadratic divergences in the cosmological constant.…”

String theory and the path to unification: A review of recent developments

“…However, despite numerous attempts and various proposals [110,78], it is not known whether there exist four-dimensional non-supersymmetric string models which also have vanishing cosmological constant. Thus, it is not yet known whether there exist any non-supersymmetric string models which are stable beyond tree level.…”