According to Peskin, p.414, at the bottom, as part of calculating the ##\beta## functions of a theory, we need to fix the counter terms by setting the "typical invariants" built from the external leg momenta to be of order ##−M^2##. For a 4-point function, these invariants are s, t and u obviously. What are the typical invariants of a three-point function? Are they just any combination of the incoming momenta, like ##p^2_1## or ##p_1\cdot p_2## or ##\not{\!p}_1\cdot\not{\!p}_2##, etc., where ##p_1, p_2## are two momenta on the external legs?(adsbygoogle = window.adsbygoogle || []).push({});

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# Typical Momentum Invariants of a 3-Point Function

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