I Why is there an additional prefactor in equation (12.52) of Peskin's QFT book?

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The discussion revolves around the additional prefactor of (-ig) in equation (12.52) of Peskin's QFT book, specifically concerning external leg corrections. The user expresses confusion about why this coupling constant is included, as it is not typically seen with external leg prefactors. The conversation highlights the importance of understanding the role of coupling constants in field renormalization counterterms. Clarifications are sought regarding the implications of this prefactor on calculations and physical interpretations. Understanding this aspect is crucial for accurate application of quantum field theory principles.
thatboi
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Hey all,
I am currently having trouble understanding equation (12.52) in Peskin's QFT book. Specifically the term for external leg corrections, in which they tack on an additional prefactor of ##(-ig)##. Normally with external leg prefactors, we don't see the coupling constant multiplied onto the field renormalization counterterm so why is such a prefactor included here?
Thanks.
 

Thread 'Angular Momentum Vector and Its Magnitude'

For the quantum state ##|l,m\rangle= |2,0\rangle## the z-component of angular momentum is zero and ##|L^2|=6 \hbar^2##. According to uncertainty it is impossible to determine the values of ##L_x, L_y, L_z## simultaneously. However, we know that ##L_x## and ## L_y##, like ##L_z##, get the values ##(-2,-1,0,1,2) \hbar##. In other words, for the state ##|2,0\rangle## we have ##\vec{L}=(L_x, L_y,0)## with ##L_x## and ## L_y## one of the values ##(-2,-1,0,1,2) \hbar##. But none of these...
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