2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/49027The computation of the polarized amplitudes and cross section of the processes $γν\toγγν$, $γγ\to γν\barν$ and $ν\barν\to γγγ$ is described. We used an effective lagrangian approach for energies below the threshold for $e^+e^-$ pair production and the complete computation at higher energies for application in supernova dynamics. Leading contributions of physics beyond the SM are also commented.9 pages, Revtex, epsfig, axodraw. Talk given at 34th Rencontres de Moriond: Electroweak Interactions and Unified Theories, Les Arcs, France, 13-20 Mar 1999High Energy Physics - Phenomenologytext