Name: Vladyslav Shtabovenko (email_not_shown)
Date: 05/19/17-11:37:54 AM Z


Dear Ula,

in this case you are missing a declaration of L and R
as noncommutative quantities.

By default, FeynCalc will treat every symbol that has not been
explicitly declared to be noncommutatuve, as a c-number. The following
works fine

DeclareNonCommutative[L, R]
R = GA[6];
L = GA[7];
yiPR = YiPR L + YiPRCC R;
ys1 = Ys1 L + Ys1CC R;
ys2 = Ys2 L + Ys2CC R;
SetMandelstam[s, t, u, p1, p2, -q1, -q2, mc1, mc2, ms1, ms2];

AmpSquare =
   Tr[yiPR.(GS[p1] - mc1 ID).ys1.(GS[p2 - q2] + mb ID).ys2.(GS[p2] +
        mc2 ID)] // Simplify;

ID = 1; Res1 = AmpSquare

Clear[ID, Res2]
ID = GA[6] + GA[7];
Res2 = AmpSquare

(Res1 - Res2) // DiracSimplify[#, DiracSubstitute67 -> True] &

Here DiracSubstitute67 merely replaces GA[6] and GA[7] by their
explicit values, i.e. 1/2(1+GA[5]) and 1/2(1-GA[5]) respectively.
Otherwise the difference is proportional to (GA[6]+GA[7]-1)

Cheers,
Vladyslav

Am 19.05.2017 um 11:24 schrieb Ula:
> Dear Vladyslav,
>
> Thanks for the fast reply and your great work with FeynCalc. I checked that many examples with chiral projectors indeed yield correct results now, but not all of them. In the example below, Res1 is consistent with my own calculations.
>
> (*Definitions*)
>
> In[2]:= R = GA[6];
>
> In[3]:= L = GA[7];
>
> In[4]:= yiPR = YiPR L + YiPRCC R;
>
> In[5]:= ys1 = Ys1 L + Ys1CC R;
>
> In[6]:= ys2 = Ys2 L + Ys2CC R;
>
> In[7]:= SetMandelstam[s, t, u, p1, p2, -q1, -q2, mc1, mc2, ms1, ms2];
>
> In[8]:= AmpSquare :=
> Tr[yiPR.(GS[p1] - mc1 ID).ys1.(GS[p2 - q2] + mb ID).ys2.(GS[p2] +
> mc2 ID)] // Simplify;
>
> (*Correct Result*)
>
> In[9]:= ID = 1; Res1 = AmpSquare;
>
> (*Wrong Result*)
>
> In[10]:= Clear[ID, Res2]
>
> In[11]:= ID = GA[6] + GA[7]; Res2 = AmpSquare;
>
> (*Difference*)
>
> In[12]:= Res1 - Res2 // Simplify
>
> Out[12]= mc2 (2 mc1^2 + mc2^2 + ms2^2 - s - u) (YiPR Ys1 Ys2 +
> YiPRCC Ys1CC Ys2CC)
>
>
> All the best,
> Ula
>
>
>
>
>
>
>
>
> Hi,
>
> thanks for the bug report. It is a bug that affects terms like
> (L1 GA[7] + R1 GA[6]) where both projectors appear multiplied with
> different constants. Should be now fixed. Please reinstall FeynCalc 9.2
> and let us know if you encounter any further issues.
>
> Cheers,
> Vladyslav
>
> Am 17.05.2017 um 11:02 schrieb Ula:
>> Dear FeynCalc users,
>>
>> In ``official" FeynCalc examples the identity matrix is not used under the trace. However, it seems that sometimes this yields wrong results when chiral projectors are present. Is this an expected bahavior, or I am doing something wrong? (I'm using FeynCalc 9.2.0 with Mathematica 8.0.4.)
>>
>> (*Definitions*)
>>
>> In[2]:= ID = GA[6] + GA[7];
>>
>> In[3]:= y1 = L1 GA[7] + R1 GA[6];
>>
>> In[4]:= y2 = L2 GA[7] + R2 GA[6];
>>
>>
>> (*Worng result*)
>>
>> In[5]:= Tr[y1.(GS[p2] + m2).y2.(GS[p1] - m1)] // FCE
>>
>> Out[5]= -2 (L2 R1 + L1 R2) (m1 m2 - SP[p1, p2])
>>
>> (*Correct result*)
>>
>> In[6]:= Tr[y1.(m2).y2.(-m1)]
>>
>> Out[6]= -2 m1 m2 (L1 L2 + R1 R2)
>>
>>
>> (*Correct result*)
>>
>> In[7]:= Tr[y1.(GS[p2] + m2 ID).y2.(GS[p1] - m1 ID)] // Simplify // FCE
>>
>> Out[7]= -2 m1 m2 (L1 L2 + R1 R2) + 2 (L2 R1 + L1 R2) SP[p1, p2]
>>
>>
>> Thanks and best wishes,
>> Ula
>>
>



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