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maverick280857
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Hi,
I'm trying to convince myself (mathematically) that energy is conserved at the vertex in [itex]e^-e^+[/itex] annihilation, while solving Exercise 3.5(b) of Halzen and Martin's book (page 83).
I am looking at the time dependent term in the scattering amplitude [itex]T_{fi}[/itex] alone, to recover the delta function term which asserts the energy conservation. I know that I can look at the process in forward time or backward time, with the roles of the e+ and e- reversed.
Suppose the energies of the incoming electron and positron are E and E' respectively, whereas the energy of the outgoing photon is [itex]\omega[/itex] ([itex]\hbar = 1[/itex]).
From what I understand, the transition amplitude is proportional to
[tex]\int dt\,(e^{-i(-E')t})^{*}e^{-i\omega t}e^{-iEt} = 2\pi\delta(E+E'+\omega)[/tex]
which gives the wrong answer of course, since the argument of the delta function should be [itex]E+E'-\omega[/itex].
I believe I am making a mistake in interpreting their "rule":
What does this mean? I'm a bit confused with the convention.
Thanks in advance.
I'm trying to convince myself (mathematically) that energy is conserved at the vertex in [itex]e^-e^+[/itex] annihilation, while solving Exercise 3.5(b) of Halzen and Martin's book (page 83).
I am looking at the time dependent term in the scattering amplitude [itex]T_{fi}[/itex] alone, to recover the delta function term which asserts the energy conservation. I know that I can look at the process in forward time or backward time, with the roles of the e+ and e- reversed.
Suppose the energies of the incoming electron and positron are E and E' respectively, whereas the energy of the outgoing photon is [itex]\omega[/itex] ([itex]\hbar = 1[/itex]).
From what I understand, the transition amplitude is proportional to
[tex]\int dt\,(e^{-i(-E')t})^{*}e^{-i\omega t}e^{-iEt} = 2\pi\delta(E+E'+\omega)[/tex]
which gives the wrong answer of course, since the argument of the delta function should be [itex]E+E'-\omega[/itex].
I believe I am making a mistake in interpreting their "rule":
The rule is to form the matrix element,
[tex]\int d^{4}x\,\phi^{*}_{outgoing}V\phi_{ingoing}[/tex]
where ingoing and outgoing always refer to the arrows on the particle (electron) lines.
What does this mean? I'm a bit confused with the convention.
Thanks in advance.
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