Heavy Higgs signal-background interference in gg → VV in the Standard Model plus real singlet

For the Standard Model extended with a real scalar singlet field, the modification of the heavy Higgs sig- nal due to interference with the continuum background and the off-shell light Higgs contribution is studied for gg → ZZ,WW → 4 lepton processes at the Large Hadron Col- lider. Interference effects can range from O(10 %) to O(1) effects for integrated cross sections. Despite a strong cancel- lation between the heavy Higgs-continuum and the heavy Higgs-light Higgs interference, the full interference is clearly non-negligible and modifies the heavy Higgs line shape. A |MVV − Mh2| <� h2 cut mitigates interference effects to O(10 %) or less. A public program that allows one to simu- late the full interference is presented.