Polyakov, A.M. (1975). "Interaction of goldstone particles in two dimensions. Applications to ferromagnets and massive Yang-Mills fields". Phys. Lett. B 59 (1): 79–81. Bibcode:1975PhLB...59...79P. doi:10.1016/0370-2693(75)90161-6.
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Polyakov, A.M. (1975). "Interaction of goldstone particles in two dimensions. Applications to ferromagnets and massive Yang-Mills fields". Phys. Lett. B 59 (1): 79–81. Bibcode:1975PhLB...59...79P. doi:10.1016/0370-2693(75)90161-6.