Non-tachyonic semi-realistic non-supersymmetric heterotic-string vacua Johar M. Ashfaque, Panos Athanasopoulos, Alon E. Faraggi and Hasan Sonmez Eur. Phys. J. C, 76 4 (2016) 208 Published online: 15 April 2016 DOI: 10.1140/epjc/s10052-016-4056-2