Proton Stability, Gauge Coupling Unification and a Light $Z^{\prime }$ in Heterotic-string Models

Abstract

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.

20 pages, 2 figures, references added, minor corrections -- accepted for publication in PRD

References in corpus (12)

• Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC
• Observation of a new boson with mass near 125 GeV in pp collisions at sqrt(s) = 7 and 8 TeV
• Chiral family classification of fermionic Z2xZ2 heterotic orbifold models
• Spinor-Vector Duality in fermionic Z2XZ2 heterotic orbifold models
• Classification of Heterotic Pati-Salam Models
• Z_2 x Z_2 Heterotic Orbifold Models of Non Factorisable Six Dimensional Toroidal Manifolds
• Top Quark Mass in Exophobic Pati--Salam Heterotic String Model
• String Derived Exophobic SU(6)xSU(2) GUTs
• Spinor-Vector Duality in Heterotic String Orbifolds
• A Novel String Derived Z' With Stable Proton, Light-Neutrinos and R-parity violation
• Discrete R-symmetry anomalies in heterotic orbifold models
• Little Z' Models

Cited by in corpus (12)

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• A Light Z' Heterotic-String Derived Model
• Extra $Z^{\prime }$s and $W^{\prime }$s in Heterotic--String Derived Models
• Light Z' in Heterotic String Standard-like Models
• The Flipped SU(5) String Vacua Classification: A Variation Of The SO(10) Breaking Basis Vector
• The LHC di-photon excess and Gauge Coupling Unification in Extra $Z^{\prime }$ Heterotic-String Derived Models
• Sterile Neutrinos in String Derived Models
• Niemeier Lattices in the Free Fermionic Heterotic-String Formulation
• Precision studies for string derived $Z^{\prime }$ dynamics at the LHC
• $Z^{\prime }$s and sterile neutrinos from heterotic string models: exploring $Z^{\prime }$ mass exclusion limits
• Light $U(1)$s in heterotic string models