José Leonel Torres. and Yépez García, V. M. (1987) “A bound for the photon mass from the angular distribution of cosmic background radiation”, Revista Mexicana de Física, 34(1), pp. 69–73. Available at: https://rmf.smf.mx/ojs/index.php/rmf/article/view/1967 (Accessed: 21 January 2025).