Abstract
We study the impact of Higgs precision measurements at a high-energy and high-luminosity linear electron positron collider, such as CLIC or the ILC, on the parameter space of a strongly interacting Higgs boson. Some combination of anomalous couplings are already tightly constrained by current fits to electroweak observables. However, even small deviations in the cross sections of single and double Higgs production, or the mere detection of a triple Higgs final state, can help establish whether it is a composite state and whether or not it emerges as a pseudo-Nambu-Goldstone boson from an underlying broken symmetry. We obtain an estimate of the ILC and CLIC sensitivities on the anomalous Higgs couplings from a study of WW scattering and hh production which can be translated into a sensitivity on the compositeness scale 4\pi f, or equivalently on the degree of compositeness \xi=v^2/f^2. We summarize the current experimental constraints, from electroweak data and direct resonance searches, and the expected reach of the LHC and CLIC on \xi and on the scale of the new resonances.
Highlights
From the Standard Model (SM) in the Higgs couplings
We study the impact of Higgs precision measurements at a high-energy and high-luminosity linear electron positron collider, such as CLIC or the ILC, on the parameter space of a strongly interacting Higgs boson
Our main result is that V V → hh at CLIC offers about half the reach on the scale of compositeness as single Higgs production at a 500 GeV ILC
Summary
Under the assumption that the mass scale at which new states appear is large, mρ mh, the recently discovered Higgs boson can be described by means of an effective Lagrangian. From the Lagrangian in eq (2.1), at leading order in the derivative expansion, it follows A(s, t, u) = (1 − a2)s/v2 and Ahh(s, t, u) = (a2 − b)s/v2 In both these cases the scattering amplitude defines a coupling strength. One might consider a situation in which future experiments constrain the Higgs couplings to be close to their SM value, so that only small deviations are allowed In this case it is convenient to adopt a more specific effective description in which h is assumed to be part of an SU(2)L doublet H and the Lagrangian is expanded in powers of the H field (as well as in the number of derivatives). One can distinguish the case of a generic SILH, where cH can have any value, from that of a PNGB Higgs
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