Issadykov, A., M. Ivanov, S. Zhaugasheva, G. Nurbakova, G. Saidullaeva, and B. Mukushev. “Diquark State of a_0 (980) Meson and Its Decay Width Calculation in Covariant Quark Model”. Recent Contributions to Physics, vol. 2015, no. 3, Aug. 2015, pp. 56-62, https://bph.kaznu.kz/index.php/zhuzhu/article/view/944.