Name: Thibaut Cousin 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_at_HIDDEN-E-MAIL]
web : http://clrwww.in2p3.fr
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