Name: Nefedov Maxim (email_not_shown)
Date: 05/11/13-07:25:08 PM Z


---------- Перенаправленное сообщение ----------
От: *Nefedov Maxim*
Дата: суббота, 11 мая 2013 г.
Тема: Box-diagrams, rational parts and OneLoop
Кому: feyncalc@feyncalc.org

  Hi!
  Trying to calculate box diagrams with OneLoop (Mathematica 7 + FC 8.2.0)
I obtained the different results in the seemingly equivalent calculations:
------------------------------------------------------------------
ScalarProduct[q1, q1] = 0;
ScalarProduct[q2, q2] = 0;
ScalarProduct[q3, q3] = 0;
den = FAD[{q, 0}, {q - q1, 0}, {q - q1 - q2, 0}, {q - q1 - q2 - q3,
    0}];

(*Doing OneLoop with q^2*q^mu*q^nu in numerator and then contracting with
g_munu*)
ex1 = PaVeReduce[
  Contract[OneLoop[q, den*SP[q, q]*FV[q,mu]*FV[q, nu]]*
    MT[mu, nu]]]

(*Doing OneLoop with q^4 in numerator*)
ex2 = PaVeReduce[OneLoop[q, den*SP[q, q]^2]]
------------------------------------------------------------------
 The results are different:

   ex1-ex2=I*Pi^2/2

 It looks like that in this two cases, the rational part of the answer (the
part which is finite in the limit D->4, but not proportional to the basis
scalar integrals) is treated in a different way, and I can not guess how to
use OneLoop to obtain always the correct answers.
  Thanks in advance for any help.
               Maxim Nefedov



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