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Master Dissertation

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A ′ 2(x1, x2) = ˜ T1(x1)T1(x2) = −T1(x1)T1(x2)<br />

= e 2 γ µ<br />

abγν cd : ψa(x1)ψb(x1) :: ψc(x2)ψd(x2) : Aµ(x1)Aν(x2)<br />

<br />

: ψa(x1)ψb(x1)ψ c(x2)ψd(x2) :<br />

= e 2 γ µ<br />

ab γν cd<br />

= e 2 γ µ<br />

ab γν cd<br />

+ : ψ a(x1) | ψb(x1)ψ c(x2) | ψd(x2) :<br />

+ : | ψ a(x1)ψb(x1)ψ c(x2)ψd(x2) | :<br />

+ : | ψ a(x1) | ψb(x1)ψ c(x2) | ψd(x2) | :<br />

<br />

×<br />

<br />

: ψa(x1)ψb(x1)ψ c(x2)ψd(x2) :<br />

: Aµ(x1)Aν(x2) : + : | Aµ(x1)Aν(x2) | :<br />

+ 1<br />

i S(+)<br />

bc (x1 − x2) : ψa(x1)ψd(x2) :<br />

+ 1<br />

i S(−)<br />

da (x2 − x1) : ψb(x1)ψc(x2) :<br />

− S (+)<br />

bc (x1 − x2)S (−)<br />

da (x2<br />

<br />

− x1)<br />

<br />

×<br />

: Aµ(x1)Aν(x2) : +gµνiD (+)<br />

0 (x1 − x2)<br />

<br />

<br />

<br />

. (8.1)<br />

From (5.8) we see that the retarded distribution is given by (8.1) simply by<br />

substituting x1 ↔ x2. For convenience we also interchange the indices<br />

µ ↔ ν, a ↔ c and b ↔ d, arriving at<br />

R ′ 2(x1, x2) = T1(x2) ˜ T1(x1) = −T1(x2)T1(x1)<br />

<br />

: ψa(x1)ψb(x1)ψ c(x2)ψd(x2) :<br />

= e 2 γ µ<br />

ab γν cd<br />

− 1<br />

i S(+)<br />

da (x2 − x1) : ψb(x1)ψc(x2) :<br />

− 1<br />

i S(−)<br />

bc (x1 − x2) : ψa(x1)ψd(x2) :<br />

− S (+)<br />

da (x2 − x1)S (−)<br />

bc (x1<br />

<br />

− x2)<br />

<br />

×<br />

: Aµ(x1)Aν(x2) : +gµνiD (+)<br />

0 (x2 − x1)<br />

67<br />

<br />

. (8.2)

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