Higgs characterisation in the presence of theoretical uncertainties and invisible decays

Abstract

While the Higgs characterisation programme is well under way, direct signs for new physics beyond the Standard Model remain elusive. Performing a fit of fully differential Higgs production cross sections at the LHC to a subset of Higgs-relevant effective operators, we discuss the extent to which theoretical uncertainties can limit the sensitivity in such a new physics search programme. Extending the dimension-6 Higgs Effective Field Theory framework by introducing new light degrees of freedom that can contribute to an invisible (or undetectable) Higgs decay width h → φφ, we show how differential coupling fits can disentangle effects from non-Standard Model couplings and an invisible decay width, as present in many new physics scenarios, such as Higgs-portal dark matter. Including the so-called off-shell measurement that has been advocated as a sensitive determination of the Higgs width in the κ framework, we show explicitly that this method does not provide complementary sensitivity for scale-separated new physics m h m φ , which is favoured in beyond the Standard Model scenarios that relate astrophysics and collider phenomenology in the light of non-observation of new physics during run 1 of the LHC.

Current and future constraints on Higgs couplings in the nonlinear Effective Theory

“…After having scrutinized the current limits on the Higgs electroweak chiral Lagrangian parameters c i in the previous section, we would like to address here the potential for improvements of such constraints at the end of the LHC life-cycle (see [53,60] for studies including also the information from differential Higgs distributions) and at future Higgs factories. We therefore consider several scenarios:…”

The Ĥ-parameter: an oblique Higgs view

“…An important consequence of this fact is that the one-loop process involving an off-shell Higgs boson, gg → h → ZZ, is insensitive to modifications of the Higgs boson propagator within an EFT, since all dimension-6 terms cancel, leaving only the modification of the Higgs Yukawa coupling to the top quark which is, in any case, better constrained from on-shell measurements [35][36][37].…”

Angles on CP-violation in Higgs boson interactions

“…Precision studies of the Higgs boson in-teractions, in particular CP-violating interactions, can therefore provide a window into the dynamics of the early Universe and can help us to unravel the mechanism underlying the matter-antimatter asymmetry. 1 The current constraints on the Higgs boson interactions provided by the ATLAS and CMS experiments at the Large Hadron Collider (LHC) still allow coupling deviations of 10% (or larger) from the SM predictions [17][18][19][20][21][22][23]. As such, they are too loosely constrained to provide a fine-grained picture of electroweak symmetry breaking.…”