# Axion-electron decoupling in nucleophobic axion models

## TL;DR

This paper demonstrates that in DFSZ-like axion models with three Higgs doublets, axion-electron decoupling can occur naturally without fine-tuning, especially influenced by the quark mass ratio, relaxing astrophysical bounds.

## Contribution

It shows that axion-electron decoupling is achievable in DFSZ-like models with three Higgs doublets without additional tuning, highlighting the importance of the quark mass ratio.

## Key findings

- Axion-electron decoupling can be naturally realized in specific DFSZ models.
- The quark mass ratio $m_u/m_d \\sim 1/2$ is key to enabling decoupling.
- Decoupling relaxes astrophysical bounds on axion mass.

## Abstract

The strongest upper bounds on the axion mass come from astrophysical observations like the neutrino burst duration of SN1987A, which depends on the axion couplings to nucleons, or the white-dwarf cooling rates and red-giant evolution, which involve the axion-electron coupling. It has been recently argued that in variants of DFSZ models with generation-dependent Peccei-Quinn charges an approximate axion-nucleon decoupling can occur, strongly relaxing the SN1987A bound. However, as in standard DFSZ models, the axion remains in general coupled to electrons, unless an ad hoc cancellation is engineered. Here we show that axion-electron decoupling can be implemented without extra tunings in DFSZ-like models with three Higgs doublets. Remarkably, the numerical value of the quark mass ratio $m_u/m_d\sim 1/2$ is crucial to open up this possibility.