Six-photon scattering (3→3)

$\gamma\gamma\gamma \to \gamma\gamma\gamma$

Three photons scatter into three photons via a fermion hexagon loop. No tree-level contribution exists — this is an intrinsically quantum process like light-by-light scattering but at higher order. Requires a closed fermion loop with six photon insertions.

Corresponds to the sixth-order term in the Euler-Heisenberg effective Lagrangian. Even more suppressed than light-by-light scattering.

No diagrams cataloged for this process yet.