Towards classification of SO(10) heterotic string vacua

We report some recent progress towards classification of phenomenologically appealing heterotic string models in the Free Fermionic Formulation. We focus on a class of Z(2) x Z(2) models with SO(10) space-time gauge symmetry and study their main phenomenological aspects. We further consider reducing the gauge symmetry to the Pati-Salam gauge group SU(4) x SU(2)(L) x SU(2)(R) and impose a series of phenomenological constraints including the existence of gauge symmetry breaking Higgs particles and the elimination of exotic fractionally charged states. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim