Confinement effects from interacting chromo-magnetic and axion fields

We study a non-Abelian gauge theory with a pseudo scalar coupling \phi \epsilon ^{\mu \nu \alpha \beta} F_{\mu \nu}^a F_{\alpha \beta}^a in the case where a constant chromo-electric, or chromo-magnetic, strength expectation value is present. We compute the interaction potential within the framework of gauge-invariant, path-dependent, variables formalism. While in the case of a constant chromo-electric field strength expectation value the static potential remains Coulombic, in the case of a constant chromo-magnetic field strength the potential energy is the sum of a Coulombic and a linear potentials, leading to the confinement of static charges