Born–Infeld axion–dilaton electrodynamics and electromagnetic confinement

A generalization of Born–Infeld non-linear vacuum electrodynamics involving axion and dilaton fields is constructed with couplings dictated by electromagnetic duality and SL(2,R) symmetries in the weak field limit. Besides the Newtonian gravitational constant the model contains a single fundamental coupling parameter b0. In the absence of axion and dilaton interactions it reduces in the limit b0↦∞ to Maxwellʼs linear vacuum theory while for finite b0 it reduces to the original Born–Infeld model. The spherically symmetric static sector of the theory is explored in a flat background spacetime in the Jordan frame where numerical evidence suggests the existence of axion–dilaton bound states possessing confined electric flux.