Zero-energy resonance effects in atomic processes within a plasma environment

We investigate the emergence of zero-energy resonance effects in atomic processes occurring within a plasma. By applying the final-state interaction theory we uncover the presence of these effects for particular configurations of density and temperature. We study the distortions that these resonances might produce in the corresponding cross sections whenever the relative momentum of a pair of charged particles intervening in the atomic process vanishes. We exemplify this general theory by applying it to the study of ionization processes by photon or ion impact. Finally we demonstrate that while for certain configurations of density and temperature these resonances might be blurred out by inhomogeneities; in others, the plasma might be tuned to the conditions for a zero-energy resonance, producing cross sections many times larger than standard estimates at the energy threshold. (paper)