 He also developed the Belavin S-matrices, exactly solvable models in two-dimensional relativistic theories in (1981).He co-authored the BPZ paper (1984) with Alexander Polyakov and Alexander Zamolodchikov on two-dimensional conformal field theory, which became important for string theory.With Vadim Knizhnik he made the Belavin–Knizhnik theorem on dual amplitudes in string theory (1986).