Eur. Phys. J. C (2011) 71: 1842
https://doi.org/10.1140/epjc/s10052-011-1842-8

Regular Article - Theoretical Physics

Investigation of quasi-realistic heterotic string models with reduced Higgs spectrum

¹ CASPER, Department of Physics, Baylor University, Waco, TX, 76798-7316, USA
² Department of Mathematical Sciences, University of Liverpool, Liverpool, L69 7ZL, UK
³ Mitchell Institute, Department of Physics, Texas A&M, College Station, TX, 77843-4242, USA

^* e-mail: Jared_Greenwald@baylor.edu

Received: 3 October 2011
Published online: 15 December 2011

Abstract

Quasi-realistic heterotic-string models in the free fermionic formulation typically contain an anomalous U(1) that leads to supersymmetry breaking. Supersymmetry is restored by imposing F- and D-flatness on the vacuum. A three generation free fermionic standard-like model which did not admit stringent F- and D-flat directions has been presented (Cleaver et al. in Phys. Rev. D 78, 046009, 2008) and it was argued that all the moduli in that model were fixed. The particular property of that model was the reduction of the untwisted Higgs spectrum by a combination of symmetric and asymmetric internal dimension boundary conditions with respect to the internal fermions associated with the compactified dimensions. This reduction occurred without the need or presence of flat directions. In this paper we extend the analysis of free fermionic models with reduced Higgs spectrum to models with the same internal space but with modified gauge groups: SO(10) or flipped SU(5) subgroup. We show that all the models studied in this paper do admit stringent flat directions. Currently, the only examples of models that do not admit stringent flat directions are the standard-like models of Cleaver et al. (Phys. Rev. D 78, 046009, 2008). We comment on the relationship between flat directions and reduced Higgs in free fermionic models as well as the possible connection between moduli stabilization and model phenomenology.