Axion Masses as an Inevitable Consequence of Supersymmetry Breaking

Abstract: We investigate a supersymmetric framework in which soft supersymmetry-breaking effects provide the dominant origin of Peccei--Quinn (PQ) symmetry breaking and axion mass generation. In the supersymmetric limit the theory possesses an exact PQ symmetry and a massless axion, while the inclusion of soft terms proportional to the gravitino mass induces spontaneous PQ breaking, stabilizes the saxion direction, and generates a mass for the axion. As a consequence, the axion, saxion, and axino masses are all controlled by the supersymmetry-breaking scale, leading to a correlated and predictive spectrum of axion-like states. The presence of explicit soft PQ-breaking terms raises the question of vacuum alignment and CP violation. We show that although the axion mass does not originate from QCD instantons, the induced strong CP phase is parametrically suppressed by the hierarchy between the QCD-induced and soft-induced axion masses. As a result, the explicit breaking does not generate an observable CP-violating vacuum angle across the parameter space of interest. We analyze the phenomenological implications of this scenario, including axion lifetimes, axion--photon couplings, and laboratory, astrophysical, and cosmological constraints. Direct confrontations with beam-dump and collider searches, together with Big Bang nucleosynthesis bounds, demonstrate that a substantial region of parameter space remains viable and testable. The framework thus provides a self-consistent and phenomenologically rich realization of axion-like particles whose masses arise predominantly from soft supersymmetry breaking.