Dominance of virtual Delbrück scattering for the photon emission by nuclei in relativistic electron-nucleus and nucleus-nucleus collisions

We consider the contribution of virtual Delbrück scattering to the photon emission by nuclei in the collision of two ultra-relativistic nuclei Z1Z2→Z1Z2γ and electron-nucleus collisions eZ→eZγ, in the photon energy range m≪Eγ≪mγ, where m is the electron mass and γ is the Lorentz factor of the colliding nucleus. The discussed process has no infrared divergence. The total cross section is 50 barn for the Pb-Pb collisions at the LHC collider. The spectral distribution obtained is considerably larger than for ordinary nuclear bremsstrahlung in the same photon energy range.