This is more or less what I tried but it leads to unsolvable integrals..
A new idea is the substitution
x_i \rightarrow \frac{a_i}{1+a_4}
which leads to
\int_0^\infty da_4 \int_0^1 da_1..da_3 (1+a_4)^{2z} \frac{\delta(1-a_1-a_2-a_3)}{(a a_1 a_2 + b a_3 a_4)^{z+2}}
doing a similar...
Homework Statement
Determine the first three terms of the Laurent expansion in z of
f(z)=\int_0^1 dx_1..dx_4 \frac{\delta(1-x_1-x_2-x_3-x_4)}{(x_1 x_2 a + x_3 x_4 b)^{2+z}},\quad a,b>0
2. The attempt at a solution
I tried expanding around z = -2.
f(z)=\sum_{n=-\infty}^\infty a_n...