- #1
Vic Sandler
- 4
- 3
I tried to derive eqn (9.94) on page 192 of the second edition of Mandl and Shaw QFT and failed. Can someone help me see what I am doing wrong?
Ignoring factors that do not change from eqn (9.92) to eqn (9.94), noting that f(k) has been set to 1, and dropping terms linear in k and k squared as described in the text, I get:
[tex]\frac{\gamma^{\alpha}(\not{p'}+m)\gamma^{\mu}(\not{p}+m)\gamma_{\alpha}}{((p'-k)^2 - m^2)((p-k)^2 - m^2)}[/tex]
[tex] = \gamma^{\mu}\frac{(-2p'p)}{(-2p'k)(-2pk)} + \frac{4m(p' + p)^{\mu}}{(-2p'k)(-2pk)} + \gamma^{\mu}\frac{(-2m^2)}{(-2p'k)(-2pk)}[/tex]
The first term on the right hand side is the same as in the book, but divided by -2. Perhaps the other two terms combine in some way to fix it up, but I don't see it. I also don't see what terms are meant by the author when he says "the dots indicate terms which are finite in the limit [itex]\lambda \rightarrow 0[/itex]" since none of the terms involve [itex]\lambda[/itex].
Ignoring factors that do not change from eqn (9.92) to eqn (9.94), noting that f(k) has been set to 1, and dropping terms linear in k and k squared as described in the text, I get:
[tex]\frac{\gamma^{\alpha}(\not{p'}+m)\gamma^{\mu}(\not{p}+m)\gamma_{\alpha}}{((p'-k)^2 - m^2)((p-k)^2 - m^2)}[/tex]
[tex] = \gamma^{\mu}\frac{(-2p'p)}{(-2p'k)(-2pk)} + \frac{4m(p' + p)^{\mu}}{(-2p'k)(-2pk)} + \gamma^{\mu}\frac{(-2m^2)}{(-2p'k)(-2pk)}[/tex]
The first term on the right hand side is the same as in the book, but divided by -2. Perhaps the other two terms combine in some way to fix it up, but I don't see it. I also don't see what terms are meant by the author when he says "the dots indicate terms which are finite in the limit [itex]\lambda \rightarrow 0[/itex]" since none of the terms involve [itex]\lambda[/itex].