Polarized and unpolarized off-shell H^→ ZZ→ 4 decay above the 2mZ threshold

An analysis of the off-shell H^→ ZZ → ̄₁₁̄₂₂ decay width is presented for both unpolarized and polarized Z gauge bosons in the scenario with the most general H^*ZZ vertex function, which is given in terms of two $CP$-even (bZ and cZ) and one $CP$-odd (bZ) anomalous couplings. The SM contributions to the H^*ZZ coupling up to the one-loop level are also included. Explicit analytic results for the unpolarized and polarized H^→ ZZ → ̄₁₁̄₂₂ square amplitudes and the four-body phase space are presented, out of which several observable quantities can be obtained straightforwardly. As far as the numerical analysis is concerned, a cross-check is performed via MadGraph5_aMC@NLO, where our model was implemented with the aid of FeynRules. We then consider the most stringent bounds on anomalous complex H^*ZZ couplings and analyze the effects of the polarizations of the Z gauge bosons through the polarized H^→ ZZ → ̄₁₁̄₂₂ decay width as well as left-right and forward-backward asymmetries, which are found to be sensitive to new-physics effects. Particular focus is put on the effects of the absorptive parts of the anomalous H^*ZZ couplings, which have been largely overlooked up to now in LHC analyses. It is found that the studied observable quantities, particularly the left-right asymmetries, can be helpful to look for effects of $CP$-violation in the H^*ZZ coupling and set bounds on the absorptive parts. For completeness, we also analyze the case of unpolarized Z gauge bosons.