A golden probe of nonlinear Higgs dynamics

Abstract

The most salient generic feature of a composite Higgs boson resides in the nonlinearity of its dynamics, which arises from degenerate vacua associated with the pseudo-Nambu–Goldstone (PNGB) nature of the Higgs boson. It has been shown that the nonlinear Higgs dynamics is universal in the IR and controlled only by a single parameter f , the decay constant of the PNGB Higgs. In this work we perform a fit, for the first time, to Wilson coefficients of O(p4) operators in the nonlinear Lagrangian using the golden H→4L decay channel. By utilizing both the “rate” information in the signal strength and the “shape” information in the fully differential spectra, we provide limits on the Goldstone decay constant f , as well as O(p4) Wilson coefficients, using Run 2 data at the LHC. In rate measurements alone, the golden channel prefers a negative ξ = v2/ f 2 corresponding to a non-compact coset structure. Including the shape information, we identify regions of parameter space where current LHC constraint on f is still weak, allowing for ξ 0.5 or ξ −0.5. We also comment on future sensitivity at the high-luminosity upgrade of the LHCwhich could allow for simultaneous fits to multiple Wilson coefficients.