A mass for the dual axion

TL;DR

This paper explores a modified axion model where the dual axion gains mass, leading to instanton suppression and a novel confinement mechanism akin to vortex solitons in superconductors.

Contribution

It introduces a new framework where the dual axion acquires mass, addressing the shift symmetry breaking and instanton confinement in axion physics.

Findings

Dual axion mass causes axion string screening.

Instanton configurations are exponentially suppressed.

Models demonstrate dynamical confinement of instantons.

Abstract

In this article we study a modification of axion physics in which the dual axion acquires a mass. This mass explicitly breaks the shift symmetry of the dual axion. The potential breaking of this shift symmetry poses a dual axion quality problem. When the dual axion acquires a mass, the axion gets eaten and becomes the longitudinal degree of freedom of a massive vector field. In this phase, axion strings are screened and far-separated instanton configurations are exponentially suppressed. This confinement of instantons corresponds to the worldline action of a particle-like soliton traveling between the instantons analogous to Abrikosov/Nielsen-Oleson vortex solitons that stretch between confined magnetic monopoles in a superconductor. We calculate the cost of this additional worldline suppression and provide several models in which both the confined instantons and confining worldline are dynamical.