2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/90288There are a number of papers dedicated to the description of free particles and antiparticles with zero mass and spin 1/2. A great many equations with different C, P, T properties have been proposed and the impression could be formed that there are many nonequivalent theories for zero-mass particles. The purpose or this paper is to show that it is not the case and to describe all nonequivalent equations.4 pagesQuantum PhysicsMathematical PhysicsExactly Solvable and Integrable Systemstext