# Mandelstam variables positive-definiteness

by Clausius
Tags: mandelstam, positivedefiniteness, variables
 P: 4 Let's consider a two-body scattering $$a+b\to c+d.$$ Prove that the quantitiy $$t=(p_c-p_a)^2\leq 0$$ where p_c is a four-vector and the square is taken with the mostly-minus metrics.

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