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Light-Light Scattering

For a long time, it is believed that the light by light scattering is described properly by the Lagrangian density obtained by Heisenberg and Euler. Here, we present a new calculation which is based on the modern field theory technique. It is found that the light-light scattering is completely different from the old expression. The reason is basically due to the unphysical condition (gauge condition) which was employed by the QED calcualtion of Karplus and Neumann. The correct cross section of light-light scattering at low energy of $(\fracω{m} \ll 1)$ can be written as $ \displaystyle{\frac{dσ}{dΩ}=\frac{1}{(6π)^2}\frac{α^4} {(2ω)^2}(3+2\cos^2θ+\cos^4θ)}$.