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Cepeda, M., No, J. M., Ramos, C., Sanda Seoane, R. M., & Zurita, J. (2025). Exotic h → Za Higgs decays into τ leptons. J. High Energy Phys., 07(7), 009–25pp.
Abstract: Exotic Higgs decays are among the most promising areas to be explored at the High-Luminosity LHC, given the unprecedentedly large amount (similar to 3 x 10(8)) of 125 GeV Higgs bosons that will be produced. In this context, we propose a new search channel for which the Higgs boson decays to a (leptonically decaying) Z boson and a light BSM pseudoscalar a, which subsequently decays to a pair of tau-leptons (h -> Za -> ll tau tau). After performing a validation of existing ATLAS and CMS exotic Higgs decay searches in related channels, we analyze the HL-LHC projected sensitivity of our a -> tau tau search, targeting the kinematic region where the exotic Higgs decay is two-body. We are able to probe pseudoscalar masses m(a) is an element of [5, 33] GeV by leveraging both leptonic and hadronic tau decays, and establish model-independent 95% C.L. sensitivity projections on the branching fraction BR(h -> Za) x BR(a -> tau tau). These a -> tau tau projections yield a competitive probe of light pseudoscalars, which depending on the model can become significantly more sensitive than projections from existing experimental searches in a -> μμand a -> gamma gamma final states. Finally, we explore the potential of our search to probe an Axion-Like-Particle (ALP) solution to the muon (g – 2) anomaly (when taken face-value), finding that our proposed h -> Za, a -> tau tau search can provide valuable constraints on such ALP scenario, in complementarity with existing h -> Za, a -> gamma gamma experimental searches.
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Delgado, R. L., Gomez-Ambrosio, R., Martinez-Martin, J., Salas-Bernardez, A., & Sanz-Cillero, J. J. (2024). Production of two, three, and four Higgs bosons: where SMEFT and HEFT depart. J. High Energy Phys., 03(3), 037–45pp.
Abstract: In this article we study the phenomenological implications of multiple Higgs boson production from longitudinal vector boson scattering in the context of effective field theories. We find compact representations for effective tree-level amplitudes with up to four final state Higgs bosons. Total cross sections are then computed for scenarios relevant at the LHC in which we find the general Higgs Effective Theory (HEFT) prediction avoids the heavy suppression observed in Standard Model Effective Field Theory (SMEFT).
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Esser, F., Madigan, M., Salas-Bernardez, A., Sanz, V., & Ubiali, M. (2024). Di-Higgs production via axion-like particles. J. High Energy Phys., 10(10), 164–22pp.
Abstract: Due to the pseudo-scalar nature of the axion-like particle (ALP), the CP-conserving production of two Higgs bosons via the ALP necessarily involves an additional Z or gamma boson. We examine the existing constraints from di-Higgs searches at Run 2 of the LHC and find that, despite the presence of extra objects in the final state, these searches are sensitive to a combination of ALP couplings to gluons and three-bosons in the TeV scale range. Additionally, we propose a specialized search strategy incorporating an energetic leptonic Z boson. This refined ALP-induced production process would allow for the identification of the h h -> 4 b-jet final state and could potentially probe the TeV scale using data from Run 2 of the LHC. This production process can also occur through a coupling between the top quark and the ALP. We translate the current constraints on di-Higgs production into new limits on the ALP-top coupling.
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