\midheading{$Ht{\bar t}$ production, processes 640--667}
\label{subsec:htt}

These processes represent the production of a Higgs boson in association
with a pair of top quarks. The calculation can be performed at LO only.

For process {\tt 640}, neither the top quarks nor the Higgs boson
decays.
In processes {\tt 641-647}, the top quarks are always
produced on-shell, which is a necessity for a gauge invariant result
from this limited set of diagrams.
Switching {\tt zerowidth} from {\tt .true.} to {\tt .false.} only affects
the Higgs and the $W$ bosons from the top quark decay.
In process {\tt 641} both the top quarks decay leptonically
and the Higgs boson decays into a pair of bottom quarks.
Consistency with
the simpler process ({\tt 640}) can be demonstrated by running process
{\tt 641} with {\tt removebr} set to true.
In process {\tt 644} the top quark decays leptonically
and the anti-top quark decays hadronically and the Higgs boson decays into a pair of bottom quarks.
In process {\tt 647} the anti-top quark decays leptonically
and the top quark decays hadronically and the Higgs boson decays into a pair of bottom quarks.

Processes {\tt 651}--{\tt 657} correspond to processes {\tt 641}--{\tt 647} but with the Higgs decaying
to two photons.
Processes {\tt 661}--{\tt 667} correspond to processes {\tt 641}--{\tt 647} but with the Higgs decaying
to two $W$-bosons which subsequently decay leptonically.