A Natural Dark Matter-Dark Energy Interaction from Axion-Monopole Dynamics

We propose a natural framework for interacting dark matter and dark energy based on axion-monopole dynamics in a dark gauge sector. Dark matter is composed of dark 't Hooft-Polyakov monopoles, while dark energy is an ultralight axion whose coupling to the dark gauge field induces an axion-dependent dyon mass through the Witten effect. This generates a direct dark matter-dark energy interaction. We show that generic models with a significant dark matter-dark energy coupling suffer from a naturalness problem: the Coleman-Weinberg potential induced by the interaction is typically much larger than the dark energy scale. In our model, the corrections arise from a monodromy tower of dyon states, allowing them to be exponentially suppressed. In the minimal setup, the interaction strength is predicted to be about 0.1%, below the sensitivity of current observations. We discuss scenarios in which cosmological population of higher-charge dyons can enhance the interaction to the percent level, producing an apparent phantom dark energy equation of state. We further show that the parameter space of the axion-monopole model preferred by fitting the Dark Energy Spectroscopic Instrument (DESI) results can also naturally explain the cosmic birefringence with a small anomaly coefficient.