**Next message:**Rakhi: "error in feyncalc contraction?"**Previous message:**Stanislav: "Several questions"**In reply to:**Stanislav: "Several questions"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]**Mail actions:**[ respond to this message ] [ mail a new topic ]

2 Stanislav

Look at the input form of the \[Epsilon]^(K2*P1*P2*K1), because what you

see is just a format used to display the contraction of LeviCivita tensor

with four 4-momenta.

Substitution rules work for the InputForm expressions. This is basically

not a FeynCalc question but a Mathematica programming question. You can

specify the custom tensor with Tensorfunction as follows

*>>> Tensorfunction[t, mu, nu, ...]
*

See http://www.feyncalc.org/FeynCalcBook/Tensorfunction/index.html for

details.

Additionally I would suggest substituting the contractions of your tensor

with four-vectors after the FeynCalc will contract the lorentz indices for

you with the vector components.

I.e. you do not need to specify the tensor in components as you mentioned

phi_mu_nu = diag{0,1,1,0} but specify it as a substitution rules for tensor

contracted with two arbitrary 4-vectors and its trace.

2015-04-09 0:30 GMT+03:00 Stanislav <noreply@feyncalc.org>:

*> Okay, several questions have arised...
*

*>
*

*> 1. Is there a way to specify my own tensor? Metric and LeviCivita are not
*

*> enough for me. For example, i'd like this one with lower indices to be
*

*> specified: phi_mu_nu = diag{0,1,1,0}
*

*>
*

*> Does FeynCalc contract this kind of predefined tensors?
*

*>
*

*> 2. When contracting 4 vectors with LeviCivita symbol i get an object like
*

*> \[Epsilon]^(K2*P1*P2*K1)
*

*>
*

*> I would like either to make this contraction explicit or to replace it
*

*> with already known expression.
*

*>
*

*> But things like
*

*> >>> M = M /. \[Epsilon]^(K2*P1*P2*K1) -> my_expression
*

*> do not work. What's going on?
*

*>
*

*>
*

-- Regards, Aliaksandr Dubrouski

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