content_image/296075.jpg content_image/296076.jpg content_image/296077.jpg content_image/296078.jpg
where the momentum integral can be evaluated using (2.13). The result is 

<img src='content_image/296075.jpg'>

Setting m = 0, the Feynman parameter integral can be evaluated in terms of the Beta function (B.11). The result is 

<img src='content_image/296076.jpg'>

This result agrees with an expression given for this integral in Ref. [97]. Also note that the result requires n$_{1}$ ≥ 0 and n$_{2}$ ≥ 0; if either of these is not satisfied the integral is a massless tadpole of the form (2.5) and is identically zero. In order to evaluate (2.18) when the mass is non-zero, note that it can be written as 

<img src='content_image/296077.jpg'>

The Feynman parameter integral can be evaluated in terms of the Gauss hypergeometric function (B.16). The result is 

<img src='content_image/296078.jpg'>

