SU(5)xSU(5) unification revisited

TL;DR

This paper revisits the minimal supersymmetric SU(5)xSU(5) grand unification model, demonstrating how gauge coupling unification can be achieved at high energies with specific intermediate particles, while considering string theory constraints.

Contribution

It shows that gauge coupling unification in SU(5)xSU(5) requires specific intermediate particles and explores the implications of string theory embedding on unification.

Findings

Gauge couplings unify at high energy with intermediate particles.

Intermediate particles can have masses in the TeV range.

Unification incompatible with perturbative string scale embedding.

Abstract

The idea of grand unification in a minimal supersymmetric SU(5)xSU(5) framework is revisited. It is shown that the unification of gauge couplings into a unique coupling constant can be achieved at a high-energy scale compatible with proton decay constraints. This requires the addition of a minimal particle content at intermediate energy scales. In particular, the introduction of the SU(2)_L triplets belonging to the (15,1)+(\bar{15},1) representations, as well as of the scalar triplet \Sigma_3 and octet \Sigma_8 in the (24,1) representation, turns out to be crucial for unification. The masses of these intermediate particles can vary over a wide range, and even lie in the TeV region. In contrast, the exotic vector-like fermions must be heavy enough and have masses above 10^10 GeV. We also show that, if the SU(5)xSU(5) theory is embedded into a heterotic string scenario, it is not possible to achieve gauge coupling unification with gravity at the perturbative string scale.