Pseudo-observables in Higgs decays

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 "κ-framework" so far adopted by the LHC experiments. The pseudo-observables are defined from on-shell decay amplitudes, allow for a systematic inclusion of higherorder 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 pseudoobservables 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 → 4 decays for the extraction of such parameters and present their predictions in the linear EFT framework.

Global effective-field-theory analysis of new-physics effects in (semi)leptonic kaon decays

“…Nonetheless, it is interesting to notice that our expressions are actually valid at any loop order if the i couplings were defined at the amplitude level for each channel (see ref. [54] for a similar description of Higgs decays). The matching to the low-energy EFT can then later performed at any desired order.…”

Electroweak Higgs production with HiggsPO at NLO QCD

“…In particular, the Higgs PO are defined from the residues of such poles [1,2]. The widelyused UFO formalism to interface model information with Monte Carlo event generators, instead, relies on amplitude generation starting from a set of interaction Feynman rules, derived from a Lagrangian.…”

“…The widelyused UFO formalism to interface model information with Monte Carlo event generators, instead, relies on amplitude generation starting from a set of interaction Feynman rules, derived from a Lagrangian. While the PO are strictly defined from gauge-invariant analytic properties of on-shell scattering amplitudes, the resulting amplitude decomposition can effectively be reproduced by the tree-level matrix elements derived from the following effective Lagrangian [1,2],…”

“…The framework of Higgs pseudo-observables (PO) allows to describe in great generality Higgs production [1] and decay [2] processes in terms of few parameters defined from the properties of the relevant on-shell physical amplitude. 1 In particular, h → 4 f decays and electroweak Higgs production processes, associated pp → Zh and pp → W h production (V H) as well as vector boson fusion (VBF) production pp → h j j, can be completely characterized by a set of onshell correlation functions 0|T {J μ f (x), J ν f (y), h(0)}|0 , where J μ f, f are the corresponding fermionic currents for each process.…”

Effective Field theories and pseudo observables in the quest for physics beyond the standard model

“…The study of couplings is very interesting because they can be extracted directly from Green's functions, in particular they are the residues of the poles after removing 1PI terms [11,12]. For every process we look at (i.e.…”