Interference effects for H --> WW/ZZ --> l anti-nu_l anti-l nu_l searches in gluon fusion at the LHC

WW/ZZ interference for Higgs signal and continuum background as well as signal-background interference is studied for same-flavour l anti-nu_l anti-l nu_l final states produced in gluon-gluon scattering at the LHC for light and heavy Higgs masses with minimal and realistic experimental selection cuts. For the signal cross section, we find WW/ZZ interference effects of O(5%) at M_H = 126 GeV. For M_H >= 200 GeV, we find that WW/ZZ interference is negligible. For the gg continuum background, we also find that WW/ZZ interference is negligible. As general rule, we conclude that non-negligible WW/ZZ interference effects occur only if at least one weak boson of the pair is dominantly off-shell due to kinematic constraints. The subdominant weak boson pair contribution induces a correction to the signal-background interference, which is at the few percentage point level before search selection cuts. Optimised selection cuts for M_H >~ 600 GeV are suggested.