A mass for the dual axion

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.