Wigner functions and quantum kinetic theory of polarized photons

We derive the Wigner functions of polarized photons in the Coulomb gauge with the ħ expansion applied to quantum field theory, and identify side-jump effects for massless photons. We also discuss the photonic chiral vortical effect for the Chern-Simons current and zilch vortical effect for the zilch current in local thermal equilibrium as a consistency check for our formalism. The results are found to be in agreement with those obtained from different approaches. Moreover, using the real-time formalism, we construct the quantum kinetic theory (QKT) for polarized photons. By further adopting a specific power counting scheme for the distribution functions, we provide a more succinct form of an effective QKT. This photonic QKT involves quantum corrections associated with self-energy gradients in the collision term, which are analogous to the side-jump corrections pertinent to spin-orbit interactions in the chiral kinetic theory for massless fermions. The same theoretical framework can also be directly applied to weakly coupled gluons in the absence of background color fields.

Short-scale quantum kinetic theory including spin–orbit interactions

We present a quantum kinetic theory for spin-1/2 particles, including the spin–orbit interaction, retaining particle dispersive effects to all orders in $$\hbar $$ ħ , based on a gauge-invariant Wigner transformation. Compared to previous works, the spin–orbit interaction leads to a new term in the kinetic equation, containing both the electric and magnetic fields. Like other models with spin–orbit interactions, our model features “hidden momentum”. As an example application, we calculate the dispersion relation for linear electrostatic waves in a magnetized plasma, and electromagnetic waves in a unmagnetized plasma. In the former case, we compare the Landau damping due to spin–orbit interactions to that due to the free current. We also discuss our model in relation to previously published works. Graphic abstract