Srednicki — Quantum Field Theory · Problem 87.5

The Higgs decay to massive gauge bosons proceeds through the cubic coupling in the Standard Model Lagrangian, where the decay rate depends on the Higgs-boson-gauge-boson vertex strength and phase space. Since the Higgs mass exceeds twice the $Z$ mass, both channels are kinematically open; the key is computing the matrix element squared for each process, then integrating over the two-body decay phase space. The $W$ and $Z$ couplings to the Higgs differ by a factor related to the weak mixing angle, so expect different partial widths even though both are two-body decays.

The Higgs decay to massive gauge bosons proceeds through the cubic coupling in the Standard Model Lagrangian, where the decay rate depends on the Higgs-boson-gauge-boson vertex strength and phase space. Since the Higgs mass exceeds twice the $Z$ mass, both channels are kinematically open; the key is computing the matrix element squared for each process, then integrating over the two-body decay phase space. The $W$ and $Z$ couplings to the Higgs differ by a factor related to the weak mixing angle, so expect different partial widths even though both are two-body decays.