New non-supersymmetric heterotic string theory with reduced rank and exponential suppression of the cosmological constant

Abstract

We study the heterotic asymmetric orbifold model in which supersymmetry is broken by the stringy Schark-Schwarz mechanism. This model is a natural non-supersymmetric extension of CHL strings and can also be interpreted as the interpolating model between the $E_{8}\times E'_{8}$ theory and the non-supersymmetric $E_{8}$ theory. The enhancement of gauge groups, of which the rank is reduced to $8+d$, is explored. In particular, the enhancement to non-simply-laced groups is possible with $d\geq 2$, as well as in the CHL model. We also give the conditions that the massless matter spectrum must satisfy. Moreover, the one-loop cosmological constant is evaluated in the regime where supersymmetry is asymptotically restored, and we show that the exponential suppression can occur unless $d=1$.