Modified Higgs sectors and NLO associated production

Many beyond the Standard Model (BSM) scenarios involve Higgs couplings to additional electroweak fields. It is well established that these new fields may modify h -> gamma gamma and h -> gamma Z decays at one-loop. However, one unexplored aspect of such scenarios is that by electroweak symmetry one should also expect modifications to the hZZ coupling at one-loop and, more generally, modifications to Higgs production and decay channels beyond tree-level. In this paper we investigate the full BSM modified electroweak corrections to associated Higgs production at both the LHC and a future lepton collider in two simple SM extensions. From both inclusive and differential NLO associated production cross sections we find BSM-NLO corrections can be as large as O (greater than or similar to 10%) when compared to the SM expectation, consistent with other precision electroweak measurements, even in scenarios where modifications to the Higgs diphoton rate are not significant. At the LHC such corrections are comparable to the involved QCD uncertainties. At a lepton collider the Higgs associated production cross section can be measured to high accuracy (O (1%) independent of uncertainties in total width and other couplings), and such a deviation could be easily observed even if the new states remain beyond kinematic reach. This should be compared to the expected accuracy for a model-independent determination of the h gamma gamma coupling at a lepton collider, which is O (15%). This work demonstrates that precision measurements of the Higgs associated production cross section constitute a powerful probe of modified Higgs sectors and will be valuable for indirectly exploring BSM scenarios.