Please notice that I have forwarded this mail to the forum on
www.feyncalc.org, so others (Rolf) can comment too. Please reply to
1) It does indeed seem as if there are some problems with the display
function FeynCalcForm. I always work with the FrontEnd interface, so I
didn't notice. If you load FeynCalc from the FrontEnd e.g.
Spinor[-Momentum[p5], M5, 1] is displayed as a spinor with a negative
momentum argument. Not as u or v. The u or v display is caused by FeynCalc
automatically setting $PrePrint to FeynCalcForm when loaded from the
command line. You can change this behaviour with the commands FI and FC.
v[-p5] should be v[p5] like before. If you evaluate a Spinor alone (not in
a Dot product), this is still the behaviour:
In:= Spinor[-Momentum[p5], M5, 1]
Out= v[p5, M5]
The mass argument is not displayed in v[-p5] in the last of your examples.
2) This is a behaviour seen only when working on the command line. So
probably also a problem with FeynCalcForm.
3) The simplification applied to the output by default might have changed
but you can still apply things like DiracSimplify, Calc or Mathematica's
Points 1 and 2 seem to indicate possible bugs. I will look at this. Rolf,
do you have any comments?
At 18:33 05-03-2001 +0100, you wrote:
>I sent you two mails earlier. This time I am sending you a typical
>mathematica file to rum under the FeynCalc. Under the main body of the
>file I pointed out the difference between the outputs from the earlier
>(FeynCalc2.2beta.m (1995)) and the latest versions of FeynCalc.
>Specifically I like to understand following specific things. Would you
>kindly find your convenience to help me in this regard.
>1. The convention for the spinors: If I use simply the input function
> 'Spinor' (which is still there in the new version) to specify the
> spinors, then I am bit confused with the convention adopted for the
> sign of the momentum in the argument of the spinor (for u and v
> spinors). This was somewhat clear in the older version where a
> spinor with a Negative Momentum in the argument is understood to be a
> 'v-spinor' with a Positive Momentum. In the outputs pasted below the
> attached Mathematica file, this does not hold.
> Please note that for Out in that file the first Spinor is u[-p1]
> from the Old Version while it is v[-p1] from the New version while
> I expect it to be v[p1]. On the other hand, in Out, for the Spinor
> v[p5,M5], it is what I expect. The notation somehow depends on whether
> we have a mass for the spinor or not. I pointed it out in one of
> my earlier mails. Please comment.
>2. Confusion with Complex Conjugation: The older version conjugates the
> given amplitude so that the coefficients of pl and pr are interchanged
> as compared to the original amplitude. This is not so in the New
> version. Please go through the Out.
>3. Simplification: Whenever there is a big expression (as is quite common
> with such tedious amplitudes) the degree of simplification had not been
> as usually expected. Could you please comment on whether the DEFAULT
> capacity for Simplification is enhanced in the New Version.
>Please let me know whether the simple-minded approach I took to realise
>the things really expects too much from the package! Also please let me
>know if I have faltered in some basic issues.
>Waiting eagerly for your comments.
>With best regards,
(* pl and pr are helicity projection operators defined above *)
GSZ3A:= CA1 (A1 pl+ A2 pr) FMIX1A + CA2 (A3 pl + A4 pr) FMIX2A;
EEZ:= (pl CLE+ pr CRE);
(* Following are the two fermion lines of a typical Feynman diagram *)
line2SZ3:=Spinor[p4,M4].dbe.(OL pl+OR pr).(p3s+p5s-MGJ).(GSZ3A).\
(* Amplitude and its hermitian conjugate constructed from the fermion lines *)
ampSZ3:= -I Contract[line1SZ3 GNUM line2SZ3];
spinsumSZ3:= FermionSpinSum[ampSZ3 campSZ3];
(* Outputs from Old and New Versions Compared *)
Out= u[-p1] ga[al] ga CLE + ga CRE u[p2] (*** Old ***)
Out= v[-p1] . ga[al] . (ga CLE + ga CRE) . u[p2] (*** New ***)
Out= u[p4, M4] ga[be] ga OL + ga OR gs[p3] + gs[p5] - MGJ
(ga A1 + ga A2) CA1 FMIX1A + (ga A3 + ga A4) CA2 FMIX2A
v[p5, M5] (*** Old ***)
Out= u[p4, M4] . ga[be] . (ga OL + ga OR) .
(gs[p3] + gs[p5] - MGJ) . ((ga A1 + ga A2) CA1 FMIX1A +
(ga A3 + ga A4) CA2 FMIX2A) . v[p5, M5] (*** New ***)
Out= v[p5, M5] (ga A1 + ga A2) CA1 FMIX1A +
(ga A3 + ga A4) CA2 FMIX2A gs[p3] + gs[p5] - MGJ ga OL + ga OR
ga[be*] u[p4, M4] (*** Old ***)
Out= v[-p5] . ((ga A1 + ga A2) CA1 FMIX1A +
(ga A3 + ga A4) CA2 FMIX2A) . (gs[p3] + gs[p5] - MGJ) .
(ga OL + ga OR) . ga[be*] . u[p4, M4] (*** New ***)
This archive was generated by hypermail 2b29 : 05/27/18-09:20:01 PM Z CEST