-
[1]
G. t, Hooft, Phys. Rev. Gett., 37(1976), 8; Phys. Rev., D14(1976), 3432;R. Jackiw, C. Rebbi, Phys. Rev. Lett., 37(1976), 172;C, G. Callan, R. F. 'Dashen, D. J. Gross, Phys, Lett., B63(1976), 334.[2] H. Y. Cheng, Phyr. Rep，159(1988), 4[3] G. G. Ross, "Grand Unified Theories" P152.[4] R. D, Peccei, H. R. Quinn, Phys. Rev. Lett., 38(1977), 1440.[5] Particle Data Grooup II. 1 Phys. Lett，B239(1990).[6] R. Mayle, J. R. Wilson, J. Ellis, K, Olive, D. N. Schnanm; G. Steigman, Phys. Lett., B203(1988), 189.[7] J. Preskill, M, Bwise, F. Wilczek, Phys. Lett.,B120(1983), 127;L. F. Abbott, P. Sikivie, Phys. Lett., 8120(1983), 133;M. Dine, W. Fischler, Phys. Lett., B120(1983), 137.