content_image/324171.jpg content_image/324170.jpg content_image/324169.jpg content_image/324168.jpg
The loop integral can be evaluated immediately using (2.19), which gives 

<img src='content_image/324171.jpg'>

Now, making the change of variables v = s , w = d 2 − n$_{1}$ − n$_{2}$ − s − t , the integral becomes 

<img src='content_image/324170.jpg'>

The contour integral over the variable v can now be evaluated using Barnes’ Lemma (B.15). Doing so, the integral becomes 

<img src='content_image/324169.jpg'>

The Gamma function in the denominator of (2.31) can be simplified using Eq. (B.4), which gives 

<img src='content_image/324168.jpg'>

Note that the remaining contour integral can be evaluated in terms of the generalized hyper- 

