We explore the space of non-SUSY string models via two distinct routes: the tachyon-free O(16)$\times$O(16) heterotic string in 10D and a tachyonic 10D heterotic string. We classify 4D Z$_2\times$Z$_2$ orbifolds descending from these two starting points in the free fermionic construction. Having found a potentially stable Standard-like model descending from the tachyonic 10D vacuum in arXiv:1912.00061, the approach of taking these models on equal footing with the non-tachyonic 10D models is justified provided that the tachyonic states are projected out in the four dimensional models. In both classes of models we find examples of Type 0 and Type 0bar models, i.e. models free of fermionic massless states and models free of twisted massless bosons, respectively. Moving beyond these extreme configurations we seek to classify tachyon-free vacua according to standard phenomenological criteria in both classes of model, where an SO(10) GUT is broken to the Pati-Salam subgroup. An analysis of the cosmological constant and misaligned supersymmetry in the two classes of models finds notable vacua in both cases in which N$_b$=N$_f$ at the massless level.
|Length of talk||15-25 minutes|
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