  We study the role played by the Landau-Pomeranchuk-Midgal (LPM) effect in
relativistic collisions of hadrons and heavy nuclei, within a parton cascade
model. We find that the LPM effect strongly affects the gluon multiplication
due to radiation and considerably alters the space-time evolution of the
dynamics of the collision. It ensures a multiplicity distribution of hadrons in
aggreement with the experimental proton-proton data. We study the production of
single photons in relativistic heavy ion collisions and find that the inclusion
of LPM suppression leads to a reduction in the single photon yield at small and
intermediate transverse momenta. The parton cascade calculation of the single
photon yield including the LPM effect is shown to be in good agreement with the
recent PHENIX data taken at the Relativistic Heavy-Ion Collider.
