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Evaluate one loops integral

  1. Feb 3, 2013 #1
    In evaluating the scalar triangle with two massive external legs using the Feynam parametrization, I have

    \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}}
    where [itex]C[/itex] is a constant factor and
    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
    I don't understand this factorization: how can [itex]i\eta[/itex] be factorized out?
  2. jcsd
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