Optical Probes of the Quantum Vacuum: The Photon Polarization Tensor in External Fields

Abstract

The photon polarization tensor is the central building block of an effective theory description of photon propagation in the quantum vacuum. It accounts for the vacuum fluctuations of the underlying theory, and in the presence of external electromagnetic fields, gives rise to such striking phenomena as vacuum birefringence and dichroism. Standard approximations of the polarization tensor are often restricted to on-the-light-cone dynamics in homogeneous electromagnetic fields, and are limited to certain momentum regimes only. We devise two different strategies to go beyond these limitations: First, we aim at obtaining novel analytical insights into the photon polarization tensor for homogeneous fields, while retaining its full momentum dependence. Second, we employ wordline numerical methods to surpass the constant-field limit.

Quantum reflection as a new signature of quantum vacuum nonlinearity

“…For k B only one externally set direction is left, and we encounter rotational invariance about the magnetic field axis. Here, the modes 0 and ⊥ can be continuously related to the two zero-field polarization modes [36].…”

“…Whereas the corresponding expression in the presence of a homogeneous (electro)magnetic field is explicitly known at one-loop accuracy [12,[37][38][39], no analytical results are available for generic, spatially inhomogeneous fields. Numerical insights are available from worldline Monte Carlo simulations [36,40].…”

Magnetically amplified light-shining-through-walls via virtual minicharged particles

“…(4) and (5), the photon polarization tensor in a purely magnetic field can be decomposed as follows [59,60],…”

“…To achieve this, we turn to the explicit expression of the photon polarization tensor in a purely magnetic field at one-loop accuracy (as reproduced in our notation in [60]). The photon polarization tensor of standard quantum electrodynamics is adapted to minicharged particles by substituting the electron-positron loop for a minicharged particle-antiparticle loop.…”

Qed Processes in Intense Laser Fields

“…11,29 Amongst the many models of new physics we will focus on spacetime noncommutativity in which the commutator of the spacetime co-ordinates is non-vanishing, [x µ , x ν ] = iθ µν . Remarkably, adding a plane wave background into noncommutative QED, the scattering processes discussed above still be calculated to all orders in the background field.…”