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The current commutation relations¹ and partially conserved axial-vector current (PCAC) assumption2,3 allow the calculation of the matrix elements for emission and absorption of any number of soft pions⁴ and, therefore, in particular, determine the scattering length of a pion on any target particle. In this note we give a simple formula for pion scattering on any particle but a pion⁵, and then extend this result to the more difficult case of pion-pion scattering.
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Steven Weinberg (1966) studied this question.
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