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Hi,

I have been using FeynCalc during the last four years and think I just have

found a possible bug in the OneLoop function. In particular, I recently had

to do some problem that involves the calculation of the following three

point tensor integral (I will use abbreviated FeynCalc notation from now

on):

M=FVD[k, \[Mu]]SPD[k, p]SPD[k](FAD[{k + p - q, mw}, {k + p + q, mw},

{k,my}]-FAD[{k + p - q, mw}, {k + p + q, mw}, {k, mu}])

where k is the arbitrary momentum to be integrated, p and q are external

momenta, and mw, mu and mv the masses of the particles in the loop.

Note that the only difference in the terms in parenthesis is in the last

propagator, namely there is the change my->mu. It follows that M=0 when

my=mu. Guess what? I accidentaly found that something weird is going on. I

computed M as follows

T1=OneLoop[k,FVD[k, \[Mu]]SPD[k, p]SPD[k] FAD[{k + p - q, mw}, {k + p +

q,mw}, {k, my}]]

T2=T1/.my->mu

M=T1-T2

Then I evaluated the following

M=(T1-T2) /.mu->my

The result was of course zero.

However, I accidentaly tried the following alternative and apparently

unnecessary calculation:

S1=FVD[k, \[Mu]]SPD[k, p]SPD[k] FAD[{k + p - q, mw}, {k + p + q, mw},{k,my}]

S2=FVD[k, \[Mu]]SPD[k, p]SPD[k] FAD[{k + p - q, mw}, {k + p + q, mw},{k,mu}]

M=S1-S2

Just to check my result I evaluated

Simplify[M /.mu->my]

which did not returned zero. I did not panic since I knew that S1 and S2

were expressed in terms of Passarino-Veltman functions. Therefore, I used

the PaVeReduce function

Simplify[PaVeReduce[M/.mv->my]]

Unfortunately the results was still not zero. I revised carefully the result

and there is no way that it is zero. I do not know if it has to do with a

problem with my computer or my FeynCalc installation. I am running

Mathematica 4.0 and have used FeynCalc 4.1.0.3b and 4.1.1. Also, I have

tried linux and windows XP and the problem remains. I think it might be

related to a problem with the OneLoop function. I am attaching a (zipped)

notebook (bug.nb) with the calculation and all the output that I got. I

will appreciate any help. What am I doing wrong?

Thanks.

- application/x-zip-compressed attachment: bug.zip

**Next message:**Frederik Orellana: "Re: Problem using OneLoop"**Previous message:**Frederik Orellana: "Re: Problem using OneLoop"**Next in thread:**blunden@jlab.org: "Re: Possible bug in OneLoop"**Reply:**blunden@jlab.org: "Re: Possible bug in OneLoop"**Maybe reply:**Vladyslav Shtabovenko: "Re: Possible bug in OneLoop"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]**Mail actions:**[ respond to this message ] [ mail a new topic ]

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