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Arroyo-Ureña, M. A., Ibarra, A., Roig, P., & Valencia-Perez, T. (2025). Prospects for detecting the rare heavy Higgs decay H → hγγ through the H→bbγγ channel at the LHC. J. High Energy Phys., 07(7), 106–25pp.
Abstract: We study the decay of a heavy CP-even neutral Higgs into an on-shell Standard Model-like Higgs boson and two photons, H -> h gamma gamma, in the two-Higgs doublet model. We argue that the decay channel H -> h gamma gamma, followed by the decay of the Standard Model Higgs h -> bb, could be observed at the 5 sigma level at the High-Luminosity LHC for masses of the heavy Higgs up to 950 GeV for the type-II, 650 GeV for the Lepton Specific and the Flipped 2HDMs, and 350 GeV for the type-I. We also discuss the possible role of the decay H -> h gamma gamma in discriminating among different types of 2HDMs and in enhancing the total number of events in the final state H -> bb gamma gamma compared to the cascade decay H -> hh followed by h -> gamma gamma h -> bb with identical final state (although with different kinematical distributions).
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Bahl, H., Martin Lozano, V., & Weiglein, G. (2022). Simplified models for resonant neutral scalar production with missing transverse energy final states. J. High Energy Phys., 11(11), 042–37pp.
Abstract: Additional Higgs bosons appear in many extensions of the Standard Model (SM). While most existing searches for additional Higgs bosons concentrate on final states consisting of SM particles, final states containing beyond the SM (BSM) particles play an important role in many BSM models. In order to facilitate future searches for such final states, we develop a simplified model framework for heavy Higgs boson decays to a massive SM boson as well as one or more invisible particles. Allowing one kind of BSM mediator in each decay chain, we classify the possible decay topologies for each final state, taking into account all different possibilities for the spin of the mediator and the invisible particles. Our comparison of the kinematic distributions for each possible model realization reveals that the distributions corresponding to the different simplified model topologies are only mildly affected by the different spin hypotheses, while there is significant sensitivity for distinguishing between the different decay topologies. As a consequence, we point out that expressing the results of experimental searches in terms of the proposed simplified model topologies will allow one to constrain wide classes of different BSM models. The application of the proposed simplified model framework is explicitly demonstrated for the example of a mono-Higgs search. For each of the simplified models that are proposed in this paper we provide all necessary ingredients for performing Monte-Carlo simulations such that they can readily be applied in experimental analyses.
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Botella, F. J., Branco, G. C., & Rebelo, M. N. (2010). Minimal flavour violation and multi-Higgs models. Phys. Lett. B, 687(2-3), 194–200.
Abstract: We propose an extension of the hypothesis of Minimal Flavour Violation (MFV) to general multi-Higgs models without the assumption of Natural Flavour Conservation (NFC) in the Higgs sector. We study in detail under what conditions the neutral Higgs couplings are only functions of V-CKM and propose a MFV expansion for the neutral Higgs couplings to fermions.
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Carcamo Hernandez, A. E., Vishnudath, K. N., & Valle, J. W. F. (2023). Linear seesaw mechanism from dark sector. J. High Energy Phys., 09(9), 046–18pp.
Abstract: We propose a minimal model where a dark sector seeds neutrino mass generation radiatively within the linear seesaw mechanism. Neutrino masses are calculable, since treelevel contributions are forbidden by symmetry. They arise from spontaneous lepton number violation by a small Higgs triplet vacuum expectation value. Lepton flavour violating processes e.g. μ-> e gamma can be sizeable, despite the tiny neutrino masses. We comment also on dark-matter and collider implications.
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Catumba, G., Hiraguchi, A., Hou, W. S., Jansen, K., Kao, Y. J., Lin, C. J. D., et al. (2025). Lattice investigation of custodial two-Higgs-doublet model at weak quartic couplings. J. High Energy Phys., 10(10), 214–36pp.
Abstract: The SU(2)-gauged custodial two-Higgs-doublet model, which shares the same global-symmetry properties with the standard model, is studied non-perturbatively on the lattice. The additional Higgs doublet enlarges the scalar spectrum and opens the possibility for spontaneous breaking of the global symmetry. In this work we start by showing the occurrence of spontaneous breaking of the custodial symmetry in a region of the parameter space of the model. Following this, both the spectrum and the running of the gauge coupling of are examined at weak quartic couplings in the presence of the custodial symmetry. The calculations are performed with energy cutoffs ranging from 300 to 600 GeV on a line of constant standard model physics, obtained by tuning bare couplings to fix the ratio between the masses of the Higgs and the W bosons, as well as the value of the renormalized gauge coupling at the scale of the W boson mass. The realizable masses for the additional scalar states are explored. For the choice of bare quartic couplings in this work, the estimated lower bound of these masses is found to be well below the W boson mass, and independent of the cutoff. We also study the finite temperature electroweak transition along this line of constant standard model physics, revealing properties of a smooth crossover behavior.
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Coutinho, A. M., Karan, A., Miralles, V., & Pich, A. (2025). Light scalars within the CP-conserving Aligned-two-Higgs-doublet model. J. High Energy Phys., 02(2), 057–53pp.
Abstract: In this article we study the possibility that neutral and charged scalars lighter than the 125 GeV Higgs boson might exist within the framework of the CP-conserving Aligned-two-Higgs-doublet model. Depending on which new scalar (scalars) is (are) light, seven different scenarios may be considered. Using the open-source code HEPfit, which relies on Bayesian statistics, we perform global fits for all seven light-mass scenarios. The constraints arising from vacuum stability, perturbativity, electroweak precision observables, flavour observables, Higgs signal strengths, and direct-detection results at the LEP and the LHC are taken into account. Reinterpreted data from slepton searches are considered too. It turns out that the seven scenarios contain sizeable regions of their parameter space compatible with all current data. Although not included in the global fits, the possible implications of (g – 2)mu are also addressed.
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Davila, J. M., Karan, A., Passemar, E., Pich, A., & Vale Silva, L. (2025). The Electric Dipole Moment of the electron in the decoupling limit of the aligned two-Higgs doublet model. J. High Energy Phys., 10(10), 053–44pp.
Abstract: We present a discussion of model-independent contributions to the EDM of the electron. We focus on those contributions that emerge from a heavy scalar sector that is linearly realized. In particular, we explore the decoupling limit of the aligned 2HDM. In this model, Barr-Zee diagrams with a fermion loop produce logarithmically-enhanced contributions that are proportional to potentially large new sources of CP violation. In the decoupling limit these contributions are generated by effective dimension-6 operators via the mixing of four-fermion operators into electroweak dipole operators. These logarithmic contributions are not present in more constrained versions of the 2HDM where a Z2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\mathcal{Z}}2 $$\end{document} symmetry is imposed, which then controls the basis of effective operators needed to describe the new physics contributions to the electron EDM. Thus, the Z2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\mathcal{Z}}2 $$\end{document} symmetry provides a suppression mechanism. In the course of the comparison of the results from the aligned 2HDM with the leading logarithms from SMEFT, we needed to specify or correct signs of expressions found in the literature. We then study how the experimental bounds on the electron EDM constrain the set of parameters of the aligned 2HDM.
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Fu, B. W., Ghoshal, A., King, S. F., & Hossain Rahat, M. (2024). Type-I two-Higgs-doublet model and gravitational waves from domain walls bounded by strings. J. High Energy Phys., 08(8), 237–25pp.
Abstract: The spontaneous breaking of a U(1) symmetry via an intermediate discrete symmetry may yield a hybrid topological defect of domain walls bounded by cosmic strings. The decay of this defect network leads to a unique gravitational wave signal spanning many orders in observable frequencies, that can be distinguished from signals generated by other sources. We investigate the production of gravitational waves from this mechanism in the context of the type-I two-Higgs-doublet model extended by a U(1)R symmetry, that simultaneously accommodates the seesaw mechanism, anomaly cancellation, and eliminates flavour-changing neutral currents. The gravitational wave spectrum produced by the string-bounded-wall network can be detected for U(1)R breaking scale from 1012 to 1015 GeV in forthcoming interferometers including LISA and Einstein Telescope, with a distinctive f3 slope and inflexion in the frequency range between microhertz and hertz.
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Giarnetti, A., Herrero-Garcia, J., Marciano, S., Meloni, D., & Vatsyayan, D. (2024). Neutrino masses from new Weinberg-like operators: phenomenology of TeV scalar multiplets. J. High Energy Phys., 05(5), 055–37pp.
Abstract: The unique dimension-5 effective operator, LLHH, known as the Weinberg operator, generates tiny Majorana masses for neutrinos after electroweak spontaneous symmetry breaking. If there are new scalar multiplets that take vacuum expectation values (VEVs), they should not be far from the electroweak scale. Consequently, they may generate new dimension-5 Weinberg-like operators which in turn also contribute to Majorana neutrino masses. In this study, we consider scenarios with one or two new scalars up to quintuplet SU(2) representations. We analyse the scalar potentials, studying whether the new VEVs can be induced and therefore are naturally suppressed, as well as the potential existence of pseudo-Nambu-Goldstone bosons. Additionally, we also obtain general limits on the new scalar multiplets from direct searches at colliders, loop corrections to electroweak precision tests and the W-boson mass.
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