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chen <chendy@ihep.ac.cn> wrote:
> Hi,
>
> I have a puzzle in my calculations.

This is a brute force approach, but it works. Otherwise, you might try playing with ComplexIndex.

<<HighEnergyPhysics`FeynCalc`

ScalarProduct[p0,p0]=m02;
ScalarProduct[p3,p3]=m32;
ScalarProduct[p4,p4]=0;
ScalarProduct[p0,p3]=m0*E3;
ScalarProduct[p0,p4]=m0*pf;
ScalarProduct[p3,p4]=E3*pf+pf2;
pf=(m02-m32)/2/m0;
E3=(m02 + m32)/(2*m0);

repV={epsC2->PolarizationSum[mu,muc,p0],
     epsV2->PolarizationSum[nu,nuc,p3],
     epsG2->PolarizationSum[rho,rhoc]};
amp=epsC*epsV*epsG*LC[mu,nu,lambda,tau]*FV[p3,rho]*
   FV[p3,lambda]*FV[p4,tau]//Contract;
ampstar=amp/.mu->muc/.nu->nuc/.rho->rhoc;
CS=amp*ampstar/.repV//Expand//Contract//Simplify;

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