Gradient expansion of the non-Abelian gauge-covariant Moyal star-product

Abstract: Motivated by the recent developments of gauge-covariant methods in the phase-space, a systematic method is presented aiming at the generalisation of the Moyal star-product to a non-Abelian gauge covariant one at any order. Such an expansion contains some dressing of the bare particle model by the gauge-fields explicitly, and might serve as a drastically simplifying tool for the elaborations of gauge-covariant quantum transport models. In addition, it might be of fundamental importance for the mathematical elaborations of gauge theory using the strict or deformation quantisation principles. A few already known examples of quantum kinetic theories are recovered without effort as an illustration of the power of this tool. A gauge-covariant formulation taking into account possible geometrical connections in both the position and momentum spaces is also constructed at leading orders, with applications to the generation of gauge-covariant effective theories in the phase-space. This paper is devoted to the pedestrian elaboration of the gradient expansions. Their numerous consequences will be explored in subsequent works.