Photon polarization tensor in presence of constant and arbitrary electric field

TL;DR

This paper calculates the photon polarization tensor in a constant electric field using the Schwinger proper-time formalism, providing a gauge-invariant, explicit expression valid for arbitrary field strengths and analyzing the strong field limit.

Contribution

It introduces a physically motivated tensor basis for the polarization tensor that maintains gauge invariance and explicitly shows Lorentz symmetry breaking due to the electric field.

Findings

Derived an explicit polarization tensor expression for arbitrary electric field strength.

Verified the zero-field limit recovers the vacuum polarization tensor.

In the strong field limit, only the transverse mode persists, indicating dominance of perpendicular dynamics.

Abstract

We compute the photon polarization tensor at one-loop order in the presence of a constant and uniform electric field. Our calculation is carried out for arbitrary field strength using the Schwinger proper-time formalism, and we explicitly derive an expression for the polarization tensor without approximations. We also present a complementary derivation within the strong field approximation. Our main contribution lies in expressing the polarization tensor in terms of a physically motivated tensor basis that ensures transversality and thus preserves gauge invariance. This basis, constructed from the preferred direction defined by the external electric field, makes explicit the breaking of Lorentz symmetry. We verify the consistency of our results by recovering the well-known vacuum polarization tensor in the zero-field limit and by demonstrating agreement between the strong field limit of the general expression and the result obtained directly in the strong field approximation. Interestingly, in the latter case, only one tensor structure survives, corresponding to the transverse dynamics with respect to the field direction, which highlights the dominance of perpendicular modes.