Name: Vladyslav Shtabovenko (email_not_shown)
Date: 04/01/15-03:58:39 PM Z


Hi Asher,

thanks for reporting this. The problem comes from the index renaming
in DiracReduce, that doesn't take into account that the double index can
already appear in the expression.

We will fix this in the master repository very soon. For now, you can
either remove the line

temp = Contract[temp, Rename-> True];

in DiracReduce.m, or, if you are using the development version, apply
FCRenameDummyIndices on the results of DiracReduce:

a = DiracReduce[DiracMatrix[i].DiracMatrix[j].DiracMatrix[k]] //
   FCRenameDummyIndices;
b = DiracReduce[DiracMatrix[i].DiracMatrix[j].DiracMatrix[k]] //
   FCRenameDummyIndices;
DiracSimplify[(SpinorUBar[p, m].a.SpinorU[p, m]) (SpinorUBar[k,
     m].b.SpinorU[k, m])]

Sorry for the inconvenience.

Cheers,
Vladyslav

Am 31.03.2015 um 00:55 schrieb Asher Berlin:
> Hi,
>
> I've noticed that using DiracReduce on matrices before entering them into expressions involving spinors results in errors in the final evaluation. Consider the following input below:
>
> a = DiracReduce[DiracMatrix[i].DiracMatrix[j].DiracMatrix[k]];
> b = DiracReduce[DiracMatrix[i].DiracMatrix[j].DiracMatrix[k]];
> DiracSimplify[(SpinorUBar[p, m].a.SpinorU[p, m])(SpinorUBar[k,m].b.SpinorU[k,m])]
>
> a = DiracMatrix[i].DiracMatrix[j].DiracMatrix[k];
> b = DiracMatrix[i].DiracMatrix[j].DiracMatrix[k];
> DiracReduce[(SpinorUBar[p, m].a.SpinorU[p, m])(SpinorUBar[k,m].b.SpinorU[k,m])]
>
> You'll notice that the 2 lines of output differ in one of the terms. I've tried this using FC 8.2 and FC 9 and the same discrepancy remains. Any ideas of what could be going wrong here?
>



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