Jacobian transformation problem

[vertices]

I feel so stupid for asking this question, but I want to understand how this integral:

$$\int^{\infty}_{0}d\alpha \int^{\infty}_{0} d\beta \frac{i}{[4 \pi i(\alpha + \beta)]^\frac{D}{2}} e^{[i \frac{\alpha\beta}{\alpha + \beta}p^2 - i(\alpha + \beta)m^2]}$$

can be transformed into this:

$$\int^{\infty}_{0}dx \int^{1}_{0} dy \frac{1}{[4 \pi i x]^\frac{D}{2}} e^{[-i x (m^2 -y(1-y)p^2)}$$

The change of variables are:

$$\alpha =xy$$
$$\beta = x(1-y)$$

My question is both these equations are in terms of two variables and I have never come across how to do this kind of integral. I am guessing that we just to substitute:

$$d\alpha =xdy+ydx$$

and

$$d\beta = (1-y)dx -xdy$$

into the original integral.

However, if I do this, I don't get the second expression... I get something quite messy.

Can anyone shed any light on this?

 

[mathman]

http://www.maths.abdn.ac.uk/~igc/tch/ma2001/notes/node77.html

The above (Jacobian transformation) describes how the transformation is supposed to take place.

 

[vertices]

thanks mathman:)