Neutrino Mixing and the Axion-Gluon Vertex

TL;DR

This paper proposes a novel solution to the strong CP problem by identifying the axion with the Majoron, linking neutrino physics with axion phenomenology through complex loop calculations.

Contribution

It introduces a new approach where the axion arises from lepton number symmetry breaking and is connected to neutrino properties, involving three-loop diagrams and IR anomaly-like terms.

Findings

Axion couplings are computable from SM parameters and Majorana masses.

The model links axion physics with neutrino mass mechanisms.

A non-local IR term effectively solves the strong CP problem.

Abstract

We present detailed arguments and calculations in support of our recent proposal to identify the axion arising in the solution of the strong CP problem with the Majoron, the (pseudo-)Goldstone boson of spontaneously broken lepton number symmetry. At low energies, the associated $U(1)_L$ becomes, via electroweak parity violation and neutrino mediation, indistinguishable from an axial Peccei-Quinn symmetry in relation to the strong interactions. The axionic couplings are then fully computable in terms of known SM parameters and the Majorana mass scales. The determination of these couplings involves certain three-loop diagrams, with a UV finite neutrino triangle taking over the role of the usual triangle anomaly. A main novelty of our proposal is thus to solve the strong CP problem by a non-local term that produces an anomaly-like term in the IR limit.