  We investigate the photon emission arising from the shift of the
quark/antiquark masses during the chiral phase transition in the early stage of
ultrarelativistic heavy-ion collisions. As this mass shift leads to spontaneous
creation of quark-antiquark pairs and thus contributes to the formation of the
quark-gluon plasma, our investigations are relevant in the context of
finite-lifetime effects on the photon emission from the latter. Earlier
investigations on this topic by Boyanovsky et al. were plagued by a UV
divergent contribution from the vacuum polarization and the non-integrability
of the remaining contributions in the ultraviolet domain. In contrast to these
investigations, we do not consider the photon number-density at finite times
but for free asymptotic states obtained by an adiabatic switching of the
electromagnetic interaction according to the Gell-Mann and Low theorem. This
approach eliminates possible unphysical contributions from the vacuum
polarization and renders the resulting photon spectra integrable in the
ultraviolet domain. It is emphasized that the consideration of free asymptotic
states is indeed crucial to obtain such physically reasonable results.
