Structure Of Flavor Changing Goldstone Boson Interactions

TL;DR

This paper systematically analyzes flavor-changing interactions of Goldstone bosons like Axions and Majorons, exploring their model-building aspects, couplings, and implications for new physics in rare decay processes.

Contribution

It provides a comprehensive framework for constructing and understanding flavor-changing Goldstone boson interactions across various models, including detailed proofs and model-specific features.

Findings

Proves the equivalence of physical GB components and broken generators in coupling calculations.

Details FCNC interactions in popular models like seesaw and Left-Right symmetric models.

Highlights unique features and model-specific aspects of flavor-changing GB interactions.

Abstract

General flavor changing interactions for a Goldstone boson (GB) to fermions due to a spontaneous global $U(1)_G$ symmetry breaking are discussed. This GB may be the Axion, solving the strong QCD CP problem, if there is a QCD anomaly for the $U(1)_G$ charge assignments for quarks. Or it may be the Majoron in models from lepton number violation in producing seesaw Majorana neutrino masses if the symmetry breaking scale is much higher than the electroweak scale. It may also, in principle, play the roles of Axion and Majoron simultaneously as far as providing solution for the strong CP problem and generating a small Majorana neutrino masses are concerned. Great attentions have been focused on flavor conserving GB interactions. Recently flavor changing Axion and Majoron models have been studied in the hope to find new physics from rare decays in the intensity frontier. In this work, we will provide a systematic model building aspect study for a GB having flavor changing neutral current (FCNC) interactions in both the quark and lepton sectors, or separately in the quark, charged lepton and neutrino sectors with sources of FCNC interactions identified in detail. We provide a general proof of the equivalence of using physical GB components and GB broken generators for calculating GB couplings to two gluons and two photons, and some issues related to models having spontaneous CP violation are discussed. We will also provide some details for obtaining FCNC GB interactions in several popular models, such as the Type-I, -II, -III seesaw and Left-Right symmetric models, and point out some special features in these models.