Modelling of the single-Higgs simplified template cross-sections (STXS 1.2) for the determination of the Higgs boson trilinear self-coupling

The trilinear self-coupling constant of the Higgs boson $\lambda$ can be determined via the measurement of the cross sections of the main Higgs boson production mechanisms (single-H). Such cross sections receive a $\lambda$ dependence from next-to-leading order electroweak corrections. To date, this approach provides constraints on anomalous $\lambda$ values comparable and complementary to the ones derived from the searches for the Higgs boson pair production HH. The constraints on $\lambda$ from single-H can be improved through the usage of differential cross section information. For this reason, this document provides a parametrization of the single-H cross section variations, with respect to the standard model predictions, as a function of $\lambda$ in the regions of the phase-space defined by the stage 1.2 simplified template cross section. This modelling will facilitate the combination of the single-H cross section measurements with HH searches to provide the ultimate precision on all of the Higgs boson couplings.