These processes represent the production of a Higgs boson that decays to ZZ, with subsequent decay into charged leptons. For process 128, the exact form of the triangle loop coupling a Higgs boson to two gluons is included, with both top and bottom quarks circulating in the loop. This is to be contrasted with process 116 in which only the top quark contribution is included in the effective coupling approach.

Process 129 includes only the effect of the interference of the Higgs and
gg → ZZ amplitudes. The calculation is available at LO only. LO corresponds to
O(α_{s}^{2}) in this case. The calculation of loops containing the third quark
generation includes the effect of both the top quark mass and the bottom
quark, while the first two generations are considered massless. For numerical
stability, a small cut on the transverse momentum of the Z bosons is applied:
p_{T}(Z) > 0.05 GeV. This typically removes less than 0.1% of the cross section. The
values of these cutoffs can be changed by editing src/ZZ/getggZZamps.f and
recompiling.

Process 130 includes all gg-initiated diagrams that have a Higgs boson in the
s-channel, namely the square of the s-channel Higgs boson production and
the interference with the diagrams that do not contain a Higgs boson, (i.e.
gg → Z∕γ^{*} + Z∕γ^{*}→ e^{-}e^{+}μ^{-}μ^{+}), i.e. |M_{H}|^{2} + 2|M_{H}^{*}M_{ZZ}|.

Process 131 calculates the full result for this process from gg-intitiated
diagrams. This includes diagrams that have a Higgs boson in the s-channel, the
continuum Z∕γ^{*} + Z∕γ^{*} diagrams described above and their interference,
i.e. |M_{H} + M_{ZZ}|^{2}.

Process 132 gives the result for the square of the box diagrams alone, i.e. the
process gg → Z∕γ^{*} + Z∕γ^{*}→ e^{-}e^{+}μ^{-}μ^{+}, i.e. |M_{ZZ}|^{2}.

Process 133 calculates the interference for the qg initiated process.

For those processes that include contributions from the Higgs boson, the form of
the Higgs propagator may be changed by editing the file src/Need/sethparams.f. If
the logical variable CPscheme is changed from the default value .false. to .true.
then the Higgs propagator is computed using the “bar-scheme” that is implemented
in the HTO code of G. Passarino [1, 2]. The value of the Higgs boson width has
been computed with v1.1 of the HTO code, for Higgs masses in the interval
50 < m_{H} < 1500 GeV. These values are tabulated, in 0.5 GeV increments, in the file
Bin/hto_output.dat. The widths for other masses in this range are obtained by
linear interpolation.

nplotter_ZZlept.f is the default plotting routine.

[1] S. Goria, G. Passarino and D. Rosco, The Higgs Boson Lineshape, Nucl. Phys. B864 (2012) 530 [1112.5517].

[2] G. Passarino, C. Sturm and S. Uccirati, Higgs Pseudo-Observables, Second Riemann Sheet and All That, Nucl. Phys. B834 (2010) 77 [1001.3360].