arXiv subjects

S. Heinemeyer

Publications and source records attributed to S. Heinemeyer.

At least 19 recordsLinked to original sources

arXiv2026

The 95 GeV Excess in Models with Two Higgs Doublets plus One Singlet: Model Distinction via Four-top Final States and Triple Higgs Couplings

We investigate the prospects for experimentally distinguishing the Next-to-Two-Higgs-Doublet Model (N2HDM) and the Two-Higgs-Doublet Model with a Complex Singlet (2HDMS) in the Yukawa type II realization. Both models can successfully accommodate the reported Higgs-boson excesses around 95 GeV while satisfying current theoretical and experimental constraints, leading to very similar predictions for the observed Higgs spectrum and signal strengths. We analyze how they can nevertheless be discriminated through observables sensitive to the scalar potential and the CP-odd sector. Analytical expressions for the trilinear Higgs couplings are derived, exhibiting characteristic contributions induced by the additional cubic interactions of the 2HDMS. We study the corresponding phenomenology in two complementary collider environments: four-top production at the High-Luminosity LHC, probing the different pseudoscalar sectors. In a second step we analyze Higgs pair production at a future high-energy $e^+e^-$ collider, providing direct sensitivity to the trilinear Higgs couplings. We quantify the potential to distinguish the two models by introducing the minimum deviation from the N2HDM limit required for a $2\sigma$ difference between the two models. Although our numerical analysis focuses on benchmark scenarios describing the 95 GeV excesses, the proposed approach provides a general framework for discriminating between singlet-extended Higgs sectors at future colliders.

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arXiv2026

Pseudoscalar contributions to Zh production at the LHC at 95 GeV and above

In generalizations of the Standard Models with extended scalar sectors, pseudoscalar particles will contribute to associated production of the Higgs boson discovered at the LHC, $h$, and the $Z$ boson. The pseudoscalar can be produced via gluon-gluon fusion, and as such may give contributions to $Zh$ production comparable to the value predicted by the Standard Model. We analyze this possibility in two different models, the Two Higgs Doublet Model, with and without an added complex singlet scalar, computing both the total and differential cross sections for this process. We focus on two pseudoscalar mass regions: (i) $m_A \sim 95$ GeV, to describe the di-photon excesses observed by CMS and ATLAS; (ii) 100 GeV $ \le m_A \le $ 1000 GeV, as a generic heavier pseudoscalar. A pseudoscalar with $m_A \sim 95$ GeV tends to give a contribution to the $pp \to Zh$ cross section that is too small to set new limits on the parameter spaces of the two models. Heavier pseudoscalars, on the other hand, can yield cross-section contributions larger than allowed by current LHC measurements and thus restricting regions of parameter space of these models which are in agreement with theoretical and all other experimental constraints. The increase of LHC luminosity will yield even substantially tighter constraints.

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arXiv2025

GUT-based NMSSM with Singlino Dark Matter: Describing the ATLAS/CMS Excesses

One of the main goals of the ongoing LHC program is the search for BSM physics, with EW SUSY partners still allowed with masses as low as a few hundred GeV. Over the last years, searches for the ``golden channel'', $pp \to \tildeχ^0_2 \tildeχ^\pm_1 \to \tildeχ^0_1 Z^{(*)} \, \tildeχ^0_1 W^{\pm (*)}$ show consistent excesses between CMS and ATLAS in the 2 soft-lepton and 3 soft-lepton plus missing $E_T$ searches, favoring mass scales of $m_{\tildeχ^0_2} \approx m_{\tildeχ^{\pm}_1} \ge 200$ GeV and $Δm_{21} := m_{\tildeχ^0_2} - m_{\tildeχ^0_1} \approx 20$ GeV. We analyze these excesses in the framework of the Next-to-Minimal Supersymmetric Standard Model (NMSSM). We assume a singlino dominated lighest neutralino, $\tildeχ^0_1$, as our Dark Matter (DM) candidate. The second and third lightest neutralinos, $\tildeχ^0_{2,3}$ are higgsino like, with the higgsino mixing parameter $μ$ being smaller than the soft SUSY-breaking bino and wino masses, $M_1$ and $M_2$. In particular, we assume the approximate GUT relations $M_1 \sim M_2/2 \sim M_3/6$, yielding a gluino mass $m_{\tilde g} \sim M_3 \ge 2$ TeV, in agreement with the LHC search limits. The scalar masses are assumed to heavy and do not play a role in our analysis. We demonstrate that this scenario is in agreement with all relevant experimental constraints, comprising the DM direct detection limits and the upper limit on the DM relic density, the LHC searches for SUSY particles and additional Higgs bosons, as well as the LHC Higgs-boson rate measurements. This constitutes the first explanation of the soft-lepton excesses in a model with GUT relations among the soft SUSY-breaking parameters.

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arXiv2025

Higgs Pair Production in the 2HDM: Impact of Loop Corrections to the Trilinear Higgs Couplings and Interference Effects on Experimental Limits

The results obtained at the LHC for constraining the trilinear Higgs self-coupling of the detected Higgs boson at about 125 GeV, $λ_{hhh}$, via the Higgs pair production process have significantly improved during the last years. We investigate the impact of potentially large higher-order corrections and interference effects on the comparison between the experimental results and the theoretical predictions for the pair production of the 125 GeV Higgs boson at the LHC. We use the theoretical framework of the Two Higgs Doublet Model (2HDM), containing besides the SM-like ${\cal CP}$-even Higgs boson $h$ a second ${\cal CP}$-even Higgs boson $H$, which we assume to be heavier, $m_H > m_h$. We analyze in particular the invariant mass distribution of the two produced Higgs bosons and show that the loop corrections to the trilinear Higgs couplings $λ_{hhh}$ and $λ_{hhH}$ as well as interference contributions give rise to important effects both for the differential and the total cross section. We point out the implications for the experimental limits that can be obtained in the 2HDM for the case of the resonant production of the heavy Higgs boson $H$. We emphasize the importance of the inclusion of interference effects between resonant and non-resonant contributions in the experimental analysis for a reliable determination of exclusion bounds for a heavy resonance of an extended Higgs sector.

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arXiv2025

Light Neutral Higgs-Boson Production at $e^+e^-$ Colliders in the Complex MSSM and NMSSM: A Full One-Loop Analysis

For future precision analyses of the Higgs boson at $\approx 125$ GeV, $h_{125}$, a precise knowledge of its production and decay properties is mandatory. While in the Standard Model (SM) these calculations are quite advanced, in many models beyond the SM (BSM) a precise calculation is missing so far. We present the calculation of the Higgs-strahlung cross-sections at $e^+e^-$ colliders for the light neutral Higgs boson production in the Next-to-Minimal Supersymmetric SM (NMSSM) with complex parameters (cNMSSM). The evaluation is based on a full one-loop calculation of the production mechanism $e^+e^- \to h_1 Z$, including soft, hard, and collinear photon radiation. The dependence of the Higgs boson production cross-sections on the relevant cNMSSM parameters is analyzed numerically. In certain scenarios we find sizable corrections to the Higgs-strahlung cross-section. Normally, they reach about $10%$ of the tree-level results, but can also exceed 20%. Finally, the calculation is compared to the corresponding one in the Minimal Supersymmetric SM (MSSM). The knowledge of the full one-loop contributions to the Higgs-boson production is particularly important for a sound theoretical intemeasurements at future $e^+e^-$ colliders such as the ILC, CLIC, LCF, FCC-ee, or CEPC. It is planned to implement the evaluation of the Higgs boson production cross-sections into an add-on package to the code FeynHiggs.

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arXiv2025

Large One-Loop Effects of BSM Triple Higgs Couplings on Double Higgs Production at $e^+e^-$ Colliders

The measurement of the Higgs boson self-coupling is crucial for our understanding of the nature of electroweak symmetry breaking and potential physics beyond the Standard Model (BSM). In this work, we study in the framework of the 2-Higgs-Doublet Model (2HDM) the impact of one-loop corrections to triple Higgs couplings (THCs) on the pair production of two Standard Model (SM)-like Higgs bosons $h$ at future high-energy $e^+ e^-$ colliders, focusing on the $e^+ e^- \to Zhh$ process. By including the one-loop corrections to the THCs relevant for this process, i.e. the coupling between three SM-like Higgs bosons, $λ_{hhh}$, and between the non-SM-like Higgs $H$, assumed to be heavier, and two SM-like Higgs bosons, $λ_{hhH}$, we account for the leading one-loop corrections to the di-Higgs production cross section. We show that the one-loop corrected THC $λ_{hhh}$ can be enhanced up to nearly six times its SM value, which substantially enhances the di-Higgs production cross section w.r.t. the tree-level prediction, even in the alignment limit. On the other hand, one-loop corrections to $λ_{hhH}$ can also enhance its value, potentially yielding to more prominent heavy Higgs $H$ resonant production. We explore the sensitivity to the loop-corrected $λ_{hhh}$ and the possible access to $λ_{hhH}$ via the $H$ resonant peak at a future high-energy $e^+e^-$ collider, such as the ILC. We highlight the fact that including the one-loop corrected THCs can enhance the sensitivity to the $H$ resonant peak, and therefore to $λ_{hhH}$. Finally, we discuss the required experimental precision at future $e^+e^-$ colliders necessary to achieve these sensitivities.

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arXiv2025

Sensitivity to Triple Higgs Couplings via Di-Higgs Production in the RxSM at the (HL-)LHC and future $e^+e^-$ Colliders

The real Higgs singlet extension of the Standard Model (SM) without $Z_2$ symmetry, the RxSM, is the simplest extension of the SM that features a First Order Electroweak Phase Transition (FOEWPT) in the early universe. The FOEWPT is one of the requirements needed for electroweak baryogenesis to explain the baryon asymmetry of the universe (BAU). Thus, the RxSM is a perfect example to study features related to the FOEWPT at current and future collider experiments. The RxSM has two CP-even Higgs bosons, $h$ and $H$, with masses $m_h < m_H$, where we assume that $h$ corresponds to the Higgs boson discovered at the LHC. Our analysis is based on a benchmark plane that ensures the occurence of a strong FOEWPT, where $m_H > 2 m_h$ is found. In a first step we analyze the di-Higgs production at the (HL-)LHC, $gg \to hh$, with a focus on the impact of the trilinear Higgs couplings (THCs), $λ_{hhh}$ and $λ_{hhH}$. The interferences of the resonant $H$-exchange diagram involving $λ_{hhH}$ and the non-resonant diagrams result in a characteristic peak-dip (or dip-peak) structure in the $m_{hh}$ distribution. We analyze how $λ_{hhH}$ can be accessed, taking into account the experimental smearing and binning. We also demonstrate that the approximation used by ATLAS and CMS for the resonant di-Higgs searches may fail to capture the relevant effects and lead to erroneous results. In a second step we analyze the benchmark plane at a future high-energy $e^+e^-$ collider with $\sqrt{s} = 1000$ GeV (ILC1000). We demonstrate the potential sensitivity to $λ_{hhH}$ via an experimental determination at the ILC1000.

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arXiv2024

Automated Choice for the Best Renormalization Scheme in BSM Models

The explorations of models beyond the Standard Model (BSM) naturally involve scans over the unknown BSM parameters. On the other hand, high precision predictions require calculations at the loop-level and thus a renormalization of (some of) the BSM parameters. Often many choices are possible for the renormalization scheme (RS). This concerns the choice of the set of to-be-renormalized parameters out of a larger set of BSM parameters, but can also concern the type of renormalization condition which is chosen for a specific parameter. A given RS can be well suited to yield "stable" and "well behaved" higher-order corrections in one part of the BSM parameter space, but can fail completely in other parts, which may not even be noticed numerically if an isolated parameter point is investigated, or when the higher-order BSM calculations are performed in an automated, not supervised set-up. Consequently, the (automated) exploration of BSM models requires a choice of a good RS {\em before} the calculation is performed. We propose a new method how such a choice can be performed. We demonstrate the feasibility of our new method in the chargino/neutralino sector of the Minimal Supersymmetric Standard Model (MSSM), but stress the general applicability of our method to all types of BSM models.

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arXiv2024

The CMS di-photon excess at 95 GeV in view of the LHC Run 2 results

The CMS collaboration has recently reported the results of a low-mass Higgs-boson search in the di-photon final state based on the full Run 2 data set with refined analysis techniques. The new results show an excess of events at a mass of about 95 GeV with a local significance of $2.9\,σ$, confirming a previously reported excess at about the same mass and similar significance based on the first-year Run 2 plus Run 1 data. The observed excess is compatible with the limits obtained in the corresponding ATLAS searches. In this work, we discuss the di-photon excess and show that it can be interpreted as the lightest Higgs boson in the Two-Higgs doublet model that is extended by a complex singlet (S2HDM) of Yukawa types II and IV. We show that the second-lightest Higgs boson is in good agreement with the current LHC Higgs-boson measurements of the state at 125 GeV, and that the full scalar sector is compatible with all theoretical and experimental constraints. Furthermore, we discuss the di-photon excess in conjunction with an excess in the $b \bar b$ final state observed at LEP and an excess observed by CMS in the di-tau final state, which were found at comparable masses with local significances of about $2σ$ and $3σ$, respectively. We find that the $b \bar b$ excess can be well described together with the di-photon excess in both types of the S2HDM. However, the di-tau excess can only be accommodated at the level of $1σ$ in type IV. We also comment on the compatibility with supersymmetric scenarios and other extended Higgs sectors, and we discuss how the potential signal can be further analyzed at the LHC and at future $e^+e^-$ colliders.

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arXiv2024

The 95.4 GeV di-photon excess at ATLAS and CMS

The ATLAS collaboration has recently reported the results of a low-mass Higgs-boson search in the di-photon final state based on the full Run 2 data set. The results are based on an improved analysis w.r.t. the previous analysis, which included a part of the Run 2 data, with a substantially better sensitivity. The ``model-dependent'' search carried out by ATLAS shows an excess of events at a mass of about 95.4 GeV with a local significance of $1.7\,σ$. The results are compatible with a previously reported excess at the same mass, but somewhat higher significance of $2.9\,σ$, from the CMS collaboration, also based on the full Run 2 data set. Combining the two results (neglecting possible correlations) we find a signal strength of $μ_{γγ}^{\rm ATLAS+CMS} = 0.24^{+0.09}_{-0.08}$, corresponding to an excess of $3.1\,σ$. In this work, we investigate the implications of this result, updating a previous analysis based solely on the CMS Run 2 data. We demonstrate that the ATLAS/CMS combined di-photon excess can be interpreted as the lightest Higgs boson in a Two-Higgs doublet model that is extended by a complex singlet (S2HDM) of Yukawa types II and IV, while being in agreement with all other experimental and theoretical constraints.

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arXiv2023

Role of $λ_{hH^+H^-}$ in Higgs boson decays $h$ to $bs$ in the 2HDM

Within the Two Higgs Doublet Model (2HDM) with $\mathcal{CP}$ conservation and a softly broken $Z_2$ symmetry, we analyze the flavor changing Higgs decays $h\to bs$ ($bs$ refers jointly to the two decay channels $b\bar s$ and $\bar b s$), where $h$ is identified with the SM-like Higgs boson discovered at the LHC. We provide a comprehensive study of the decay width $Γ(h \to bs)$ with particular focus on the most relevant effects from the triple Higgs coupling $λ_{hH^+H^-}$. Furthermore, we consider all the relevant theoretical and experimental constraints to determine which predictions for the $\mathrm{BR}\left(h\to bs\right)$ are still allowed by the current data. We find that the predictions for $\mathrm{BR}\left(h\to bs\right)$ in types II and III can be several orders of magnitude smaller compared to the SM value. In contrast, in type I and IV we find that the predicted enhancements in the decay rates with respect to the SM of up to about 70% and 50%, respectively, are still allowed. We discuss how these deviations from the SM are caused by interference effects controlled by the coupling $λ_{hH^+H^-}$ which can be large for very heavy $H^\pm$. To better understand the role of $λ_{hH^+H^-}$ in the $h \to bs$ decay we derive and analyze here the analytical results for the $hbs$ one-loop effective vertex that is generated by integrating out the heavy $H^\pm$.

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arXiv2023

Automated choice of the best renormalization scheme

High-precision predictions in BSM models require calculations at the loop-level and thus a renormalization of (some of) the BSM parameter. Here many choices for the renormalization scheme (RS) are possible. A given RS can be well suited to yield ``stable'' and ``well behaved'' higher-order corrections in one part of the BSM parameter space, but can fail completely in other parts. The latter may not even be noticed numerically if an isolated parameter point is investigated. Here we review a new method for choosing a ``well behaved'' RS. We demonstrate the feasibility of our new method in the chargino/neutralino sector of the Minimal Supersymmetric Standard Model (MSSM), but stress the general applicability of our method to all types of BSM models.

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arXiv2023

Higgs-mass predictions in the MSSM and beyond

Predictions for the Higgs masses are a distinctive feature of supersymmetric extensions of the Standard Model, where they play a crucial role in constraining the parameter space. The discovery of a Higgs boson and the remarkably precise measurement of its mass at the LHC have spurred new efforts aimed at improving the accuracy of the theoretical predictions for the Higgs masses in supersymmetric models. The "Precision SUSY Higgs Mass Calculation Initiative" (KUTS) was launched in 2014 to provide a forum for discussions between the different groups involved in these efforts. This report aims to present a comprehensive overview of the current status of Higgs-mass calculations in supersymmetric models, to document the many advances that were achieved in recent years and were discussed during the KUTS meetings, and to outline the prospects for future improvements in these calculations.

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arXiv2022

Sensitivity to Triple Higgs Couplings via Di-Higgs Production in the 2HDM at the (HL-)LHC

An important task of the LHC is the investigation of the Higgs-boson sector. Of particular interest is the reconstruction of the Higgs potential, i.e. the measurement of the Higgs self-couplings. Based on previous analyses, within the 2HDMs type~I and~II, we analyze several two-dimensional benchmark planes that are over large parts in agreement with all theoretical and experimental constraints. For these planes we evaluate di-Higgs production cross sections at the (HL-)LHC with a center-of-mass energy of 13 TeV at NLO in the heavy top-quark limit with the code HPAIR. We investige in particular the process $gg \to hh$, with $h$ being the Higgs boson discovered at the LHC with a mass of about 125 GeV. The top box diagram of the loop-mediated gluon fusion process into Higgs pairs interferes with the $s$-channel exchange of the two CP-even 2HDM Higgs bosons $h$ and $H$ involving the trilinear couplings $λ_{hhh}$ and $λ_{hhH}$, respectively. Depending on the size of the involved top-Yukawa and triple Higgs couplings as well as on the mass of $H$, the contribution of the $s$-channel $H$~diagram can be dominating or be highly suppressed. We find regions of the allowed parameter space in which the di-Higgs production cross section can differ by many standard deviations from its SM prediction, indicating possible access to deviations in $λ_{hhh}$ from the SM value $λ_{\rm SM}$ and/or contributions involving $λ_{hhH}$. The sensitivity to $λ_{hhH}$ is further analyzed employing the $m_{hh}$ distributions. We demonstrate how a possible measurement of $λ_{hhH}$ depends on the various experimenal uncertainties. Depending on the underlying parameter space, the HL-LHC may have the option not only to detect beyond-the-Standard-Model triple Higgs couplings, but also to provide a first rough measurement of their sizes.

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arXiv2022

The Future Circular Collider: a Summary for the US 2021 Snowmass Process

In this white paper for the 2021 Snowmass process, we give a description of the proposed Future Circular Collider (FCC) project and its physics program. The paper summarizes and updates the discussion submitted to the European Strategy on Particle Physics. After construction of an approximately 90 km tunnel, an electron-positron collider based on established technologies allows world-record instantaneous luminosities at center-of-mass energies from the Z resonance up to tt thresholds, enabling a rich set of fundamental measurements including Higgs couplings determinations at the sub percent level, precision tests of the weak and strong forces, and searches for new particles, including dark matter, both directly and via virtual corrections or mixing. Among other possibilities, the FCC-ee will be able to (i) indirectly discover new particles coupling to the Higgs and/or electroweak bosons up to scales around 7 and 50 TeV, respectively; (ii) perform competitive SUSY tests at the loop level in regions not accessible at the LHC; (iii) study heavy-flavor and tau physics in ultra-rare decays beyond the LHC reach, and (iv) achieve the best potential in direct collider searches for dark matter, sterile neutrinos, and axion-like particles with masses up to around 90 GeV. The tunnel can then be reused for a proton-proton collider, establishing record center-of-mass collision energy, allowing unprecedented reach for direct searches for new particles up to the around 50 TeV scale, and a diverse program of measurements of the Standard Model and Higgs boson, including a precision measurement of the Higgs self-coupling, and conclusively testing weakly-interacting massive particle scenarios of thermal relic dark matter.

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arXiv2022

Future Perspective for Higgs Physics

Future perspectives for Higgs physics are outlined. First it is shown that the discovered Higgs boson cannot be the Standard Model (SM) Higgs boson, motivating the investigations of Higgs sectors beyond the SM (BSM). The secure future, the HL-LHC, and the agreed upon future, an $e^+e^-$ collider, are briefly discussed. The importance of theory calculations for the full exploitation of the (anticipated) experimental data is emphasized. Finally, the complementarity of collider based Higgs physics and other types of experiments, such as gravitational wave observatories is briefly outlined.

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arXiv2022

Sensitivity and constraints to the 2HDM soft-breaking $Z_2$ parameter $m_{12}$

In this letter we study the specific sensitivity and constraints to the soft breaking $Z_2$ parameter $m_{12}$ of the Two Higgs Doublet Model (2HDM). $m_{12}$ is considered here as an input parameter of the model together with the masses of the Higgs bosons, $m_h$, $m_H$, $m_A$, $m_{H^\pm}$, the ratio of the two Higgs vacuum expectation values, $\tan β$, and $\cos(β-α)$, with $α$ and $β$ the mixing angles of the $\mathcal{CP}$-even and $\mathcal{CP}$-odd Higgs sector, respectively. We explore in particular the sensitivity to $m_{12}$ in the decays of the lightest Higgs boson $h$ to two photons, assuming: 1) that $h$ is the state observed at the LHC at $\sim 125 \ \mathrm{GeV}$, and 2) the $h$ couplings to the SM particles are SM-like, by going to the alignment limit, $\cos(β-α) = 0$. The aim of this work is to demonstrate possible constraints on $m_{12}$ from the present measurement of the di-photon signal strength, $μ_{γγ}$. These constraints are relevant in the region of the 2HDM parameter space that is allowed by all the other constraints, specifically, theoretical constraints as well as experimental constraints from LHC Higgs rate measurements, Higgs boson searches, flavor physics and precision observables. The exploration is performed in the four different Yukawa types of 2HDM, where the allowed region by all the other constraints depends on the model type. We also analyze the case that the Higgs-boson mass spectrum accommodates a possible new world average of $m_W$ including the recent CDF measurement.

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arXiv2022

CDF Measurement of $M_W$: Theory implications

The CDF collaboration recently reported a measurement of the $W$-bosos mass, $M_W$, showing a large positive deviation from the Standard Model (SM) prediction. The question arises whether extensions of the SM exist that can accommodate such large values, and what further phenomenological consequences arise from this. We give a brief review of the implications of the new CDF measurement on the SM, as well as on Higgs-sector extensions. In particular, we review the compatibility of the $M_W$ measurement of CDF with excesses observed in the light Higgs-boson searches at $\sim 95$ GeV, as well as with the Minimal Supersymmetric Standard Model in conjunction with the anomalous magnetic moment of the muon, $(g-2)_μ$.

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