$SU(5)\times{U(1)'}$ models with a vector-like fermion family

Abstract

Motivated by experimental measurements indicating deviations from the Standard Model predictions we discuss F-theory inspired models, which, in addition to the three chiral generations contain a vector-like complete fermion family. The analysis takes place in the context of $SU(5)\times U(1)'$ GUT embedded in an $E_8$ covering group which is associated with the (highest) geometric singularity of the elliptic fibration. In this context, the $U(1)'$ is a linear combination of four abelian factors subjected to appropriate anomaly cancellation conditions. Furthermore, we require universal $U(1)'$ charges for the three chiral families and different ones for the corresponding fields of the vector-like representations. Under the aforementioned assumptions, we find 192 such models which can be classified into five distinct categories with respect to their specific GUT properties. We exhibit representative examples for each such class and construct the superpotential couplings and the fermion mass matrices. We explore the implications of the vector-like states in low energy phenomenology including the predictions regarding the B-meson anomalies. The r\^ole of R-parity violating terms appearing in some particular models of the above construction is also discussed.