Minimal anomaly-free chiral fermion sets and gauge coupling unification

TL;DR

This paper identifies minimal anomaly-free chiral fermion sets beyond the standard model that enable gauge coupling unification at high energy scales, including GUT and string scales, while respecting experimental constraints.

Contribution

It introduces minimal chiral fermion sets compatible with anomaly cancellation and gauge unification, including those within SU(5) multiplets, up to dimension 50.

Findings

Some fermion sets achieve unification at GUT scales.

Certain sets allow unification at string scales.

The sets are minimal and anomaly-free, compatible with experimental bounds.

Abstract

We look for minimal chiral sets of fermions beyond the standard model that are anomaly free and, simultaneously, vectorlike particles with respect to colour SU(3) and electromagnetic U(1). We then study whether the addition of such particles to the standard model particle content allows for the unification of gauge couplings at a high energy scale, above $5.0 \times 10^{15}$ GeV so as to be safely consistent with proton decay bounds. The possibility to have unification at the string scale is also considered. Inspired in grand unified theories, we also search for minimal chiral fermion sets that belong to SU(5) multiplets. Restricting to representations up to dimension 50, we show that some of these sets can lead to gauge unification at the GUT and/or string scales.