Coherent photon bremsstrahlung and dynamics of heavy-ion collisions: Comparison of different models

Differential spectra of coherent photon bremsstrahlung in relativistic heavy ion collisions are calculated within various schematic models of the projectile-target stopping. Two versions of the degradation length model, based on a phenomenological deceleration law, are considered. The simple shock wave model is studied analytically. The predictions of these models agree in the soft photon limit, where the spectrum is determined only by the final velocity distribution of charged particles. The results of these models in the case of central Au+Au collisions at various bombarding energies are compared with the predictions of the microscopic transport model UrQMD. It is shown that at the AGS energy the coherent photon bremsstrahlung exceeds the photon yield from $\pi^0$-decays at photon energies $\omega\loo 50$ MeV.