Clara Del Pio

A correction to this paper has been published: https://doi.org/10.1007/JHEP05(2026)112

A bstract: The calculation of precise predictions for Higgs decays is a necessary ingredient for determining Higgs properties at the LHC and future colliders. We compute all two- and three- body Higgs decays at next-to-leading order (NLO) in both QCD and electroweak interactions using the dimension-6 Standard Model Effective Field Theory (SMEFT). Results for four-body Higgs decays that are accurate to NLO QCD/electroweak order in the SMEFT are obtained using the narrow width approximation. Our results are contained in a flexible Monte Carlo program, NEW i SH, that is publicly available and we illustrate the impact of the NLO electroweak corrections for HL-LHC, Tera-Z, and Higgstrahlung projections.

Several key observables of the high-precision physics program at future lepton colliders will critically depend on the knowledge of the absolute machine luminosity. The determination of the luminosity relies on the precise knowledge of some reference process, which is, in principle, not affected by unknown physics, so that its cross section can be computed within a well-established theory, like the Standard Model. Quantifying the uncertainties induced by possible new physics effects on such processes is, therefore, crucial. We present an investigation of light and heavy new physics contributions to the small-angle Bhabha process at future e + e − colliders, and we discuss possible strategies to remove the contamination due to heavy degrees of freedom by relying on observables that are independent of the absolute luminosity.