2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/116945A kinetic theory for radiation interacting with sound waves in an ultrarelativistic electron-positron plasma is developed. It is shown that the effect of a spatial spectral broadening of the electromagnetic pulse is to introduce a reduction of the growth rates for the decay and modulational instabilities. Such spectral broadening could be due to a finite pulse coherence length, or through the use of random phase filters, and would stabilize the propagation of electromagnetic pulses.8 pages, 4 figures, to appear in Phys. PlasmasPlasma Physicstext