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 hrightarrow phi phi , 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 kappa framework, we show explicitly that this method does not provide complementary sensitivity for scale-separated new physics Lambda gg m_h gg m_phi , 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.
Highlights
The continued success story of the Standard Model (SM), which has prevailed for the first 13 TeV measurements, has had a sobering effect on the potentially too optimistic expectations of a new physics discovery early on in the LHC era
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 mh mφ, 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
Since our analysis does not include any information on invisible Higgs searches, our results are applicable to invisible Higgs decay modes, e.g. H → light flavour quarks
Summary
The continued success story of the SM, which has prevailed for the first 13 TeV measurements, has had a sobering effect on the potentially too optimistic expectations of a new physics discovery early on in the LHC era. Often addressing these phenomena requires the new hidden degrees of freedom to be light compared to the electroweak scale, Ohid ∼ φ2, with mφ v (we will denote the mass of the new SM-singlet scalar of Eq (1) with mφ in the following) In such scenarios, interactions of type Eq (1) can introduce new and invisible decay channels h → φφ of the physical Higgs which can be tackled by adapted search strategies. The merit of studying effective theories of the form of Eq (1) is two-fold: we do discuss the quantitative impact of BSM physics on the Higgs sector related to light degrees of freedom, but we point out directions how BSM searches in the context of Higgs measurements can be systematically improved with regards to maximum phenomenological impact.
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