Proton stability, gauge coupling unification, and a light <i>Z</i>′ in heterotic-string models

Faraggi, Alon E ORCID: 0000-0001-7123-6414 and Mehta, Viraf M
(2013) Proton stability, gauge coupling unification, and a light <i>Z</i>′ in heterotic-string models. PHYSICAL REVIEW D, 88 (2). 105023-.

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We explore the phenomenological viability of a light Z' in heterotic-string models, whose existence has been motivated by proton stability arguments. A class of quasi-realistic string models that produce such a viable Z' are the Left-Right Symmetric (LRS) heterotic-string models in the free fermionic formulation. A key feature of these models is that the matter charges under U(1)_Z' do not admit an E6 embedding. The light Z' in the LRS heterotic-string models forbids baryon number violating operators, while allowing lepton number violating operators, hence suppressing proton decay yet allowing for sufficiently small neutrino masses via a seesaw mechanism. We show that the constraints imposed by the gauge coupling data and heterotic-string coupling unification nullify the viability of a light Z' in these models. We further argue that agreement with the gauge coupling data necessitates that the U(1)_Z' charges admit an E6 embedding. We discuss how viable string models with this property may be constructed.

Item Type: Article
Additional Information: 20 pages, 2 figures, references added, minor corrections -- accepted for publication in PRD
Uncontrolled Keywords: hep-ph, hep-ph, hep-th
Depositing User: Symplectic Admin
Date Deposited: 03 Mar 2017 09:12
Last Modified: 14 Oct 2023 12:26
DOI: 10.1103/PhysRevD.88.025006
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