Name: Thibaut Cousin (email_not_shown)
Date: 06/27/02-05:52:45 PM Z


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Le Jeudi 27 Juin 2002 15:05, vous avez écrit :
> First of all, don't usually expect to get anything reasonable out of
> factors with more than two occurrences of the same index. FeynCalc assumes
> the usual Einstein summation convention, but cannot judge what to do in
> cases like x*x.
>
> Try
>
> x=LC[a,b,c,d]FourVector[k1,a]FourVector[k2,b]FourVector[k3,c]FourVector[k4,
>d];
> y=LC[e,f,g,h]FourVector[k1,e]FourVector[k2,f]FourVector[k3,g]FourVector[k4,
>h]; x y // Contract
>
>
> W.r.t. writing out x in terms of scalar products, this would amount to
> writing out the Levi-Civita tensor in terms of Kronecker deltas. I don't
> believe this is possible?

  The LC tensor can't be a combination of Kronecker deltas, otherwise it would
be a real tensor (instead of a pseudotensor).
  But for example, I've computed by hand that:

        LC[k1,k3,w,p] = omp.R1.R3.cos(a)

knowing all the possible scalar products of k1, k3, w and p. If I can compute
this by hand, shouldn't Feyncalc be able to do it too? It just needs to
develop all 16 terms of the LC tensor, substitute the values of the scalar
products and add them.

- --
Thibaut Cousin
email : cousin@in2p3.fr
web : http://clrwww.in2p3.fr
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