Grand-Unification Scale Generation through the Anomalous U(1) Breaking

TL;DR

This paper explores how anomalous U(1) gauge symmetry can generate the grand-unification scale, favoring product gauge groups like SU(5)×U(3) and addressing key issues such as doublet-triplet splitting and proton decay suppression.

Contribution

It proposes the R-invariant natural unification model with SU(5)×U(3) gauge groups, solving the doublet-triplet splitting problem and suppressing proton decay.

Findings

Unification to a simple group requires parameter tuning.

The SU(5)×U(3) model naturally solves the doublet-triplet splitting.

R-invariance suppresses dangerous proton decay operators.

Abstract

We discuss the anomalous U(1) gauge symmetry as a mechanism of generating the grand-unification scale. We conclude that unification to a simple group cannot be realized unless some parameters are ``tuned'', and that models with product gauge groups are preferred. We consider the ``R-invariant natural unification'' model with gauge groups SU(5)_{GUT} \times U(3)_H. In this model the doublet-triplet splitting problem is solved and the unwanted GUT relation m_s = m_\mu is avoided maintaining m_b = m_\tau. Moreover, R-invariance suppresses the dangerous proton decays induced by dimension four and five operators.