addwidth

The option is used to controle the adding width of unstable particles in the amplitude calculation. The default choose is to add width. The user can choose not to add width by set the following value:

        addwidth:='no$

It is obviously that to add width will break the gauge invariance in the calculation of amplitude. It will be a higher order breaking if there is no t-channel photon connected to a fermion line with small mass. Otherwise, the breaking is serious. To deal with this serious breaking, we introduce a method and controle it by the next option.