New Prospects for Higgs Compositeness in h -> Z gamma

Abstract

We discuss novel effects in the phenomenology of a light Higgs boson within the context of composite models. We show that large modifications may arise in the decay of a composite Nambu-Goldstone boson Higgs to a photon and a Z boson, h -> Z gamma. These can be generated by the exchange of massive composite states of a strong sector that breaks a left-right symmetry, which we show to be the sole symmetry structure responsible for governing the size of these new effects in the absence of Goldstone-breaking interactions. In this paper we consider corrections to the decay h -> Z gamma obtained either by integrating out vectors at tree level, or by integrating out vector-like fermions at loop level. In each case, the pertinent operators that are generated are parametrically enhanced relative to other interactions that arise at loop level in the Standard Model such as h -> gg and h -> gamma gamma. Thus we emphasize that the effects of interest here provide a unique possibility to probe the dynamics underlying electroweak symmetry breaking, and do not depend on any contrivance stemming from carefully chosen spectra. The effects we discuss naturally lead to concerns of compatibility with precision electroweak measurements, and we show with relevant computations that these corrections can be kept well under control in our general parameter space.