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Gluon-initiated associated production boosts Higgs physics

Analyses of boosted Higgs bosons from associated production comprise some of the main search channels for the Higgs boson at the LHC. The gluon-initiated $gg\to hZ$ subprocess has largely been ignored in phenomenological analyses of boosted associated production although this contribution is sizable as the $p_T$ spectrum for this process is maximised in the boosted regime due to the top quark loop threshold. In this paper, we discuss this contribution to boosted $pp\to hZ$ analyses in detail. We find there are previously overlooked modifications of Standard Model Higgs rates at the LHC which depend on the $p_T$ cuts applied and can be significant. There are also important consequences for physics beyond the Standard Model as the $gg\to hZ$ process introduces significant dependence on the magnitude and sign of the Higgs-top quark coupling $c_t$, which is overlooked if it is assumed that associated production depends only on the Higgs-$Z$ boson coupling as $c_V^2$. This new dependence on $c_t$ impacts interpretations of Higgs rates in the contexts of Supersymmetry, Two Higgs Doublet Models, and general scenarios with modified couplings. We suggest that these effects be included in current and future LHC boosted Higgs analyses.