3. The resulting matrix (6), upon the setting of J = 0, consists of two groups (aside from the term
with numerical 1) of relevant identical terms. These terms are as written in coordinate space.
Let us take the group of terms with the numerical factor
1
12
and write this in momentum space
(8)
β« π4 π¦ β²π4 π¦
πΊ(π¦ β² β π¦)
(2π)2
πΊ( π¦ β π¦ β² )
(2π)2
πΊ(π¦ β² β π¦)
(2π)2
π΅
π΄
=
1
(2π)4
β« π4 π β« π4 π β²β« π4 π β²β²
1
βπ2 + π2 + ππ
1
βπ β²2 + π2 + ππ
1
βπ β²β²2 + π2 + ππ
πΏ4( π β π β²
+ π β²β² ) π¦ β² πΏ4( π β π β² + π β²β² ) π¦
The Dirac-delta functions in this expression represent vertices at the respective space-time points
π¦ β² and π¦. As indicated above there are three four-momentum integration variables with two
initial four-momentum vertices that we have just mentioned.
As written in coordinate space (8) can be depicted with the following Feynman graph
(Fig.1)
where at the spacetime point π¦ β² is the Dirac-delta function πΏ4( π β π β² + π β²β² ) π¦ β², while at the
spacetime point y the Dirac-delta function πΏ4( π β π β² + π β²β² ) π¦ . (Note the symmetric property of
the Dirac-delta function, πΏ4(βπ) = πΏ4( π)).
We also have the Fourier components of the propagators
(8.1)
πΜ( π) =
1
βπ2 + π2 + ππ
(8.2)
4. πΜ( π β²) =
1
βπ β²2 + π2 + ππ
and
(8.3)
πΜ( π β²β²) =
1
βπ β²β²2 + π2 + ππ
We can integrate over π β²β² at the space-time point π¦ with a picking π β²β² = k β β k so that we can
reduce (8) into (noted (k β β k )2
= (k β k β² )2
)
(9)
β« π4 π¦ β²π4 π¦
πΊ(π¦ β² β π¦)
(2π)2
πΊ( π¦ β π¦ β² )
(2π)2
πΊ(π¦ β² β π¦)
(2π)2
π΅
π΄
=
1
(2π)4
β« π4 πβ²
1
βπ β²2 + π2 + ππ
β« π4 π
1
βπ2 + π2 + ππ
1
β ( k β k β² )
2
+ π2 + ππ
πΏ4( π β² β π
+ k β k β² ) π¦ β²
In momentum space as given by (9), we have the corresponding Feynman graph
(Fig.2)
where
(9.1)
πΜ( π) =
1
βπ2 + π2 + ππ
(9.2)
πΜ( π β²) =
1
βπ β²2 + π2 + ππ
and
5. (9.3)
πΜ(k β k β² ) =
1
β (k β k β² )
2
+ π2 + ππ
In (9), we have chosen the four-momentum k as internal four-momentum and kβ as the external
four-momentum and such recognition enables us to construct the Feynman graph Fig.2.
In (9) we take note of the remaining Dirac-delta function that we write as (caution: with
symmetric integral limits)
(9.4)
πΏ4( π β² β π + k β k β² ) π¦ β² = πΏ4(0 ) π¦ β² =
1
(2π)4
β« π4 π¦ β²
This might imply a singularity if we are to base this on the basic definition of a Dirac-delta
function with an argument that is vanishing, which is πΏ4(0 ) π¦ β² = β. However, for the moment let
us take (9.4) as a definite constant.
We continue with the other group of terms that collectively go with the numerical factor
1
8
as given by (6)
in coordinate space. This we translate into momentum space
(10)
β« π4 π¦ β²π4 π¦
πΊ(π¦ β² β π¦ β² )
(2π)2
πΊ( π¦ β² β π¦ )
(2π)2
πΊ(π¦ β π¦)
(2π)2
π΅
π΄
=
1
(2π)4
β« π4 π β« π4 π β²β« π4 π β²β²
1
βπ2 + π2 + ππ
1
βπ β²2 + π2 + ππ
1
βπ β²β²2 + π2 + ππ
πΏ4( π β π "
+ π β²β² ) π¦ β² πΏ4( π β π β² + π β² ) π¦
This is depicted in the following Feynman graph
(Fig.3)
6. Refβs:
[1]W. Hollik, Quantum field theory and the Standard Model, arXiv:1012.3883v1 [hep-ph]
[2]Baal, P., A COURSE IN FIELD THEORY,
http://www.lorentz.leidenuniv.nl/~vanbaal/FTcourse.html
[3]βt Hooft, G., THE CONCEPTUAL BASIS OF QUANTUM FIELD THEORY,
http://www.phys.uu.nl/~thooft/
[4]Siegel, W., FIELDS, arXiv:hep-th/9912205 v2
[5]Wells, J. D., Lectures on Higgs Boson Physics in the Standard Model and Beyond,
arXiv:0909.4541v1
[6]Cardy, J., Introduction to Quantum Field Theory
[7]Gaberdiel, M., Gehrmann-De Ridder, A., Quantum Field Theory