Spontaneous breaking of the lepton number and invisible majoron in a 3-3-1 model C. A. S. de Pires and P. S. Rodrigues da Silva Eur. Phys. J. C, 36 3 (2004) 397-403 Published online: 14 July 2004 DOI: 10.1140/epjc/s2004-01949-3