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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Bouchhar, N., Cabrera Urban, S., Cantero, J., et al. (2025). Search for Higgs boson exotic decays into Lorentz-boosted light bosons in the four-τ final state at √s=13 TeV with the ATLAS detector. Phys. Lett. B, 870, 139843–18pp.
Abstract: A search for exotic decays of the Higgs boson into a pair of low-mass scalars that subsequently decay into tau -leptons, H -> aa -> tau(+)tau(-)tau(+)tau(-), is presented. In models with Yukawa-like couplings, the decay to tau-leptons is favoured for light a-bosons, with mass in the range of 2m(tau) < m(a) < 2m(b). Results are presented in the range of 4 GeV < m(a) < 15 GeV using the 140 fb(-1) of proton-proton collisions at root s = 13 TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider. This search focuses on the scenario where, for both di-tau pairs, one of the tau-leptons decays to hadrons and neutrinos, while the other decays to a muon and neutrinos. In this mass range, the a -> tau(+)tau(-) is Lorentz-boosted and a dedicated muon removal technique is used to reconstruct the di-tau pairs. No significant excess above the Standard Model background prediction is observed. Upper limits on (sigma(H)/sigma(SM)(H)) x B(H -> aa -> 4 tau) at 95% confidence level are provided, ranging from 0.03 to 0.10 depending on the a-boson mass.
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Bonilla, C., Romao, J. C., & Valle, J. W. F. (2016). Electroweak breaking and neutrino mass: `invisible' Higgs decays at the LHC (type II seesaw). New J. Phys., 18, 033033–21pp.
Abstract: Neutrino mass generation through the Higgs mechanism not only suggests the need to reconsider the physics of electroweak symmetry breaking from a new perspective, but also provides a new theoretically consistent and experimentally viable paradigm. We illustrate this by describing the main features of the electroweak symmetry breaking sector of the simplest type-II seesaw model with spontaneous breaking of lepton number. After reviewing the relevant `theoretical' and astrophysical restrictions on the Higgs sector, we perform an analysis of the sensitivities of Higgs Boson searches at the ongoing ATLAS and CMS experiments at the LHC, including not only the new contributions to the decay channels present in the standard model (SM) but also genuinely non-SM Higgs Boson decays, such as `invisible' Higgs Boson decays to majorons. We find sensitivities that are likely to be reached at the upcoming run of the experiments.
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Bordes, J., Hong-Mo, C., & Tsun, T. S. (2022). Resolving an ambiguity of Higgs couplings in the FSM, greatly improving thereby the model's predictive range and prospects. Int. J. Mod. Phys. A, 37(27), 2250167–10pp.
Abstract: We show that, after resolving what was thought to be an ambiguity in the Higgs coupling, the FSM gives, apart from two extra terms (i) and (ii) to be specified below, an effective action in the standard sector which has the same form as the SM action, the two differing only in the values of the mass and mixing parameters of quarks and leptons which the SM takes as Finputs from experiment while the FSM obtains as a result of a fit with a few parameters. Hence, to the accuracy that these two sets of parameters agree in value, and they do to a good extent as shown in earlier work,' the FSM should give the same result as the SM in all the circumstances where the latter has been successfully applied, except for the noted modifications due to (i) and (ii). If so, it would be a big step forward for the FSM. The correction terms are: (i) a mixing between the SM's gamma – Z with a new vector boson in the hidden sector, (ii) a mixing between the standard Higgs with a new scalar boson also in the hidden sector. And these have been shown a few years back to lead to (i') an enhancement of the W mass over the SM value,(2) – and (ii') effects consistent with the g – 2 and some other anomalies,(3) precisely the two deviations from the SM reported by experiments(4,5) recently much in the news.
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