Pseudo-observables in Higgs decays

TL;DR

This paper introduces pseudo-observables for Higgs decays, enabling systematic analysis of Higgs properties in extensions of the Standard Model without new particles below the Higgs mass.

Contribution

It defines a comprehensive set of pseudo-observables from on-shell decay amplitudes, generalizing the kappa-framework and allowing for higher-order corrections and EFT computations.

Findings

Pseudo-observables can be extracted from experimental data.

Reduction of parameters under symmetry assumptions.

Predictions for $h\to 4\ell$ decays in linear EFT.

Abstract

We define a set of pseudo-observables characterizing the properties of Higgs decays in generic extensions of the Standard Model with no new particles below the Higgs mass. The pseudo-observables can be determined from experimental data, providing a systematic generalization of the "kappa-framework" so far adopted by the LHC experiments. The pseudo-observables are defined from on-shell decay amplitudes, allow for a systematic inclusion of higher-order QED and QCD corrections, and can be computed in any Effective Field Theory (EFT) approach to Higgs physics. We analyze the reduction of the number of independent pseudo-observables following from the hypotheses of lepton-universality, CP invariance, custodial symmetry, and linearly realized electroweak symmetry breaking. We outline the importance of kinematical studies of $h\to 4\ell$ decays for the extraction of such parameters and present their predictions in the linear EFT framework.