Name: C. Sun Date: 05/15/19-07:28:38 PM Z


Dear Vladyslav and Mailing List Users,

I got stuck by something probably very trivial. In short, I wonder what is the elegant way to include the decay width in an internal propagator. I have tried to implement it as

(*after generating FA diagrams*)
ruleResonance = {
    Mchi -> Sqrt[(Mchi^2 - I*Mchi*\[CapitalGamma]chi)]
   };
CreateFeynAmp[diagram] /. M$FACouplings /. ruleResonance

However, after I apply FCFAConvert[], the minus sign is not picked up right. I think that is because all other minus signs have been wrapped as “-“ while the one I manually inserted in front of \Gamma_{\chi} is just a regular minus sign. This causes trouble as later when I do

(amp[0] (ComplexConjugate[amp[0]])) //
    FermionSpinSum[#, ExtraFactor -> 1/2] & //
           DiracSimplify // Simplify// FCE // FeynAmpDenominatorExplicit

all terms with decay width inserted are not simplified.
Any input would be appreciated.

Best,
Chen