Soa, D. V., N. H. Thao, P. V. Dong, T. T. Huong, and H. N. Long. “Neutrinoless Double Beta Decay in the Economical 3-3-1 Model”. Communications in Physics, vol. 18, no. 1, July 2008, pp. 9-18, doi:10.15625/0868-3166/18/1/10685.