other orientation of the fermion loop we obtain
Nf ag3KT M,2 + M22 + M32 ln(1/)_2
lI n(1/a)- (3 137)
1672m MM,[_.. 3
In contrast, the calculation and result for the n n2 A, n3 = V polarization is
quite a lot simpler. The expression analogous to (3-136) is
Nfag3K^ln(1/a) M I 1/
l- 16r1 2- 1 L (3-138)
The result shown in (3-48) is obtained from this one by adding the k, < 0 contribution
and multiplying by two which accounts for the other orientation of the fermion arrows in
the loop.