Name: V. Shtabovenko (email_not_shown)
Date: 07/25/18-04:22:46 PM Z


Dear FeynCalc users,

let me announce a change in the default behavior of DiracaSimplify that
has been introduced in the development version. From now on, when
applied to expressions that
contain Dirac traces, DiracSimplify will evaluate them automatically.

This was already possible since some time by setting the option
DiracTraceEvaluate to True, but the default value of this option was
False. Now it is set to True by default.
The obvious advantage is that expressions with traces should be now
simplified in a faster and more efficient way. Consider, for example

expr = DiracTrace[(mU + GSD[l - p1 - p2 - p3]).(I EL GAD[Lor3]).(mU +
       GSD[l - p3]).(I EL GAD[Lor1]).(mU +
       GSD[k]).(-((I EL mU)/(2 mX)))] Spinor[Momentum[p1, D], 0,
     1].(I EL GAD[Lor2]).Spinor[-Momentum[p2, D], 0, 1] FVD[
    Polarization[p3, -I, Transversality -> True], Lor1] MTD[Lor2, Lor3]

Normally, you would probably do something like

(expr /. DiracTrace -> Tr) // DiracSimplify //Contract // DiracSimplify

to obtain the maximally simplified version of this expression. However,
now it is sufficient to run just

DiracSimplify[expr]

which is not only simpler but also faster.

If for some reason you need to recover the old behavior, just use

SetOptions[DiracSimplify, DiracTraceEvaluate -> False]

at the beginning of you code.

Cheers,
Vladyslav



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