Enhancement of the Higgs pair production at LHC: the MSSM and extra-dimension effects

The neutral Higgs pair production at LHC is studied in the MSSM, the large extra dimension model and the Randall-Sundrum model, where the total cross section can be enhanced by more than one order of magnitude, compared to that in the SM. We have obtained the $p_{_T}$, invariant mass and rapidity distributions. Both of the extra-dimensional cases show distinctive features: The distribution shapes are almost independent of the string scale $M_{\rm S}$; the $p_{_T}$ and invariant mass distributions peak around $M_{\rm S}\sim$ TeV, while the SM and MSSM contributions drop rapidly at this high scale; the rapidity distributions show significantly narrow peaks. It is concluded that various distributions of the Higgs pair production at LHC with restrictive kinematic cuts would provide one of the most robust signals of the extra dimensional effects.