content_image/313252.jpg content_image/313251.jpg content_image/313250.jpg content_image/313249.jpg
Using the result (2.26), setting d = 4 + 2 ϵ , and working in the MS scheme, we find 

<img src='content_image/313252.jpg'>

In order to expand the hypergeometric function, it is useful to write it in series form 

<img src='content_image/313251.jpg'>

Now we must expand the sum around ϵ = 0, and because of the overall Γ ( − ϵ ) term we must expand the sum to O ( ϵ ) in order to expand the entire integral to O ( ϵ $^{0}$). First, note that for n ≥ 1 we may safely set ϵ = 0 in the sum. Extracting the n = 0 term, we have 

<img src='content_image/313250.jpg'>

Using the properties of the Gamma function, this can be written as 

<img src='content_image/313249.jpg'>

where ψ ( n ) is the Polygamma function (B.6). Evaluating the sums and performing the 

