4
votes
1answer
81 views

Why does S-matrix unitarity imply the cross section $\sigma$ $\propto$ $\frac {1}{s}$?

I'm currently learning for an oral exam in theoretical physics and as a learning aid protocols of older exams exist. In one protocol the question was asked: Why is the scattering cross section ...
4
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3answers
693 views

Unitarity of S-matrix in QFT

I am a beginner in QFT, and my question is probably very basic. As far as I understand, usually in QFT, in particular in QED, one postulates existence of IN and OUT states. Unitarity of the S-matrix ...