These processes represent the production of a virtual Z boson or photon which subsequently decays into t. The leptonic decays of the top quarks are included. Switching zerowidth from .true. to .false. only affects the W bosons from the top quark decay. Note that m34min > 0 is obligatory due to the inclusion of the virtual photon diagrams. The calculation may be only be performed at LO. This is a small contribution, but in p-collisions gives a forward backward asymmetry.
nplotter_auto.f is the default plotting routine.