Variations on the SU(5) axion

TL;DR

This paper explores different models embedding axions and seesaw mechanisms within SU(5) GUTs, revealing that their low-energy axion phenomenology is identical despite theoretical ambiguities.

Contribution

It systematically analyzes various SU(5) axion models and shows their equivalence in phenomenology due to unphysical ambiguities in PQ charges.

Findings

Models with active B-L symmetry have ambiguous PQ charges.

Different seesaw realizations are equivalent in axion phenomenology.

Unphysical ambiguities do not affect low-energy predictions.

Abstract

The simultaneous embeddings of an axion state and a seesaw mechanism within the SU(5) Grand Unification Theory, both minimal and flipped, are systematically studied. It is shown that whenever B-L is active as a global symmetry, the PQ charges of the fermions are ambiguous. Various realizations of the seesaw mechanism are then found to differ only in the way this ambiguity is resolved. But since the ambiguity is unphysical, all these models are thereby predicted to be equivalent, in the sense that the axion phenomenology is identical at the low energy scale.