= Higgs pair production =
This page contains the codes for calculating Higgs pair production at LHC through gluon fusion.
== SM ==
[[Image(SMdiagrams.png)]]
We calculated the Higgs pair production at LO for a top quark circulating in the loops (exact form factors at LO for the triangle loop and the box from [http://arxiv.org/abs/hep-ph/9603205 arxiv:9603205] [hep-ph]).
The corresponding code out of MG5 can be downloaded here : [attachment:SM.tar.gz SM]
== BSM : tthh coupling ==
[[Image(tthh.png)]]
Here we have implemented a new coupling tthh which has been described in terms of a new parameter c2 (see arxiv:1205.5444v2 [hep-ph]). You can modify its value in the block bsminputs of the paramcard. So by setting c2 to 0 you will recover the above SM result.
Again the full top mass dependence of the loop matrix elements is taken into account.
The corresponding code out of MG5 can be downloaded here : [attachment:tthh.tar.gz tthh]
== BSM : Additional heavy scalar resonance ==
[[Image(heavyscalar.png)]]
Finally in this case we have considered the possibility of having a heavy scalar H (called hh in the MG files) as an intermediate state (so that we have the additional process p p > H > h h that is taken into account). For this model in the param_card.dat the user has the freedom of modifying a wide range of parameters :
* the top yukawa coupling (via the parameter cy)
* the SM-Higgs trilinear coupling (ctr)
* the H coupling to the top (cyH)
* the H coupling to 2 SM-Higgs (ctrH)
The parameters cy and ctr are just factors that multiply the SM couplings. The couplings for the heavy scalar are obtained similarly by multiplying the corresponding SM couplings with the parameters cyH and ctrH. By default they are all fixed to 1.
Finally you can also modify :
* the H mass (MHH)
* the H decay width (WHH)
The corresponding code out of MG5 can be downloaded here : [attachment:HeavyScalar.tar.gz HeavyScalar]