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In evaluating the scalar triangle with two massive external legs using the Feynam parametrization, I have

[tex]

\int\frac{d^dl}{(2\pi)^2}\frac{1}{[l^2+i\eta][(l+p)^2+i\eta][(l+p+q_2)^2+i\eta]}=C\int_0^1 d\alpha_1 d\alpha_2 d\alpha_3\delta(1-\sum\alpha_i)\frac{1}{D^{\frac{d}{2}-3}}

[/tex]

where [itex]C[/itex] is a constant factor and

[tex]

D=-[\alpha_1\alpha_3q_1^2+\alpha_2\alpha_3q_2^2-i\eta]

[/tex]

Now the paper says:

Factorizing out [itex]−q2[/itex] with the right [itex]i\eta[/itex] prescription and defining [itex]r=\frac{q_1^2}{q_2^2}+i\eta[/itex]

we have

[tex]

D=(-1-i\eta)q_2^2\alpha_3(\alpha_1r+\alpha_2)

[/tex]

I don't understand this factorization: how can [itex]i\eta[/itex] be factorized out?

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# Evaluate one loops integral

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