arXiv subjects

Sven Heinemeyer

Publications and source records attributed to Sven Heinemeyer.

At least 19 recordsLinked to original sources

arXiv2026

HiggsTools for LHC Run 3 and Beyond

HiggsTools, including the subpackages HiggsPredictions, HiggsBounds, and HiggsSignals, is a toolbox for Beyond-the-SM (BSM) scalar phenomenology at the LHC. It provides BSM model predictions, tests the model against experimental limits from searches for BSM scalars and derives constraints from the measurements of the properties of the discovered Higgs boson. We present a variety of improvements to the HiggsTools framework, preparing it for the results of LHC Run 3 and the HL-LHC. HiggsPredictions now provides additional cross-section predictions for centre-of-mass energies of 13.6 and 14 TeV. Moreover, it now includes cross-section predictions for resonant and non-resonant Higgs-boson pair production. For HiggsBounds, we describe the recasting of searches using multi-top final states, explain their implementation and highlight the impact of the experimental sensitivity of those results. Furthermore, we discuss the implementation of coupling-dependent limits on non-resonant Higgs boson pair production, as well as the improved handling of searches conducted prior to the Higgs boson discovery. For HiggsSignals we describe several improvements for the case of scalars with mass uncertainties.

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arXiv2026

Complementarity of gravitational wave analyses and di-Higgs production in the exploration of the Electroweak Phase Transition dynamics in the RxSM

The real singlet extension of the Standard Model (SM), RxSM, is one of the simplest Beyond-the-Standard Model (BSM) theories that can accommodate a strong first-order electroweak phase transition (SFOEWPT). We survey the possible thermal histories of the early Universe in the RxSM, and find that a SFOEWPT can occur in this model as single- or two-step phase transitions. We investigate complementary approaches to probe such scenarios experimentally: either via searches for a stochastic background of gravitational waves (GWs) or via searches for di-Higgs production processes at future collider experiments: the HL-LHC, or a possible high-energy $e^+e^-$ collider. For these analyses we consistently include one-loop corrections to the trilinear Higgs couplings. We find that entirely different phenomenological signals are possible, depending on how the SFOEWPT occurs. In scenarios where such a transition is driven by the Higgs doublet direction in field space, BSM deviations in properties of the detected Higgs boson, particularly in the trilinear scalar coupling, typically lead to observable signals at colliders, while the regions of parameter space with detectable GW signals are very narrow. On the other hand, if the SFOEWPT is triggered by the singlet field direction, the detected Higgs boson is very SM-like and no signs of BSM physics would appear in di-Higgs production processes. However, strong GW signals could be produced for significant parts of the RxSM parameter space with singlet-driven SFOEWPT. This work highlights the crucial importance of exploiting complementary experimental directions to determine the dynamics of the electroweak phase transition and access the shape of the Higgs potential realised in Nature.

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arXiv2026

Investigating a strong first-order electroweak phase transition in the RxSM at future linear $e^+e^-$ colliders and LISA

The general real singlet extension of the Standard Model (SM), the RxSM, is one of the simplest theories Beyond-the-Standard Model (BSM) that can accommodate a strong first-order electroweak phase transition (SFOEWPT). We investigate the possible thermal histories of the scalar potential in the RxSM, and the regions of the model parameter space in which SFOEWPT can be realised. We then explore complementary avenues to probe such scenarios experimentally: either using searches for a stochastic background of gravitational waves (GWs), or using searches for di-Higgs production processes at future collider experiments, focusing on the case of a high-energy $e^+e^-$ collider. An important aspect of our work is that one-loop corrections to all relevant trilinear scalar couplings are consistently included both in the calculation of dynamics of the electroweak phase transition (EWPT) and in collider processes. We find entirely different phenomenological signatures for different parts of the RxSM parameter space giving rise to SFOEWPTs. On the one hand, if the SFOEWPT is driven by the singlet field, the 125 GeV Higgs boson is very SM-like and signs of BSM physics would be difficult to find at colliders, but strong GW signals could be produced. On the other hand, in scenarios where a SFOEWPT is driven by the doublet field, BSM deviations in properties of the detected Higgs boson, particularly in its trilinear self-coupling, typically lead to observable signals at colliders, while detectable GW signals are much more challenging to achieve. This work highlights the complementarity of collider experiments and cosmological observations to determine the dynamics of the EWPT and reconstruct the shape of the Higgs potential realised in Nature.

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arXiv2026

Interpretation of LHC excesses at 95 GeV and 152 GeV in an extended Georgi-Machacek model

We analyze the excesses at 95 GeV in the light Higgs-boson searches in the di-photon decay channel reported by CMS and ATLAS, which combined are at the level of three standard deviations and are compatible with the excess in the $b\bar{b}$ final state observed at LEP, together with an excess in the di-photon channel at around 152 GeV reported based on a sideband analysis. We demonstrate that these excesses can be well described in a minimally extended Georgi-Machacek (meGM) model. This is enabled by four key features of the meGM model: (1) a natural prediction for scalar boson masses of $\lesssim$200 GeV arising from the condition to describe both the Higgs boson signal at 125 GeV and the excesses at 95 GeV, (2) the prediction for a doubly charged Higgs boson that can potentially enhance the di-photon decay rates, (3) asymmetric $WW$ and $ZZ$ couplings to neutral scalar bosons that are induced by mild custodial symmetry breaking, and (4) the approximate preservation of the electroweak $ρ$ parameter to be 1 at tree level. We show in our numerical analysis that the meGM model naturally improves the fit to the LHC data around 152 GeV when describing the excesses at 95 GeV. At the same time, the model also predicts additional light CP-odd and charged scalar bosons that can be potentially probed in future experiments, which motivates dedicated searches in the upcoming LHC runs. We also present the results of sensitivity studies for the 95 and 125 GeV Higgs-boson couplings at the HL-LHC and future $e^+e^-$ colliders, which demonstrate very interesting prospects for probing the meGM model at future colliders.

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arXiv2026

Sensitivity to new physics: single-Higgs couplings vs. the trilinear Higgs coupling

The trilinear Higgs self-coupling provides a unique probe of the structure of the Higgs potential and of the nature of the electroweak phase transition, and constitutes a key target for future collider experiments. Recent studies have shown that confronting theoretical predictions for the trilinear Higgs coupling with current experimental bounds offers a powerful and complementary way to test effects of physics beyond the Standard Model (BSM), in particular those arising from extended Higgs sectors. Meanwhile, substantial progress has been achieved in the precise calculation and automation of the trilinear Higgs coupling in a wide class of BSM models. This contribution discusses several BSM scenarios, compatible with existing constraints, in which sizeable deviations in the trilinear Higgs coupling w.r.t. the Standard Model (SM) value are predicted, while other Higgs observables remain close to their SM expectations and are therefore difficult to probe experimentally. These results highlight the strong physics motivation for a precise measurement of the trilinear Higgs coupling at a future Higgs factory.

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arXiv2025

Consistent Excesses in the LHC Electroweak SUSY Searches: GUT-based Singlino/Higgsino Interpretation in the NMSSM

The search for supersymmetric models remains one of the main items on the BSM search program at the LHC, 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 ATLAS and CMS in the 2~soft-lepton and 3~soft-lepton plus missing-$E_T$ searches, assuming $m_{\tildeχ^0_2} \approx m_{\tildeχ^{\pm}_1} \gtrsim 200$ GeV and $Δm_{21} := m_{\tildeχ^0_2} - m_{\tildeχ^0_1} \approx 20$ GeV. We interpret these excesses in the framework of the Next-to-Minimal Supersymmetric Standard Model. We assume a singlino dominated lightest neutralino as a Dark Matter (DM) candidate. The second and third lightest neutralinos are higgsino like, with the higgsino mixing parameter $μ$ being smaller than the soft SUSY-breaking bino and wino masses, $M_1$ and $M_2$. We furthermore assume the approximate GUT relations $M_1 \sim M_2/2 \sim M_3/6$, with the implication for our scenario of a gluino mass $m_{\tilde{g}} \sim M_3 \gtrsim 3$ TeV. Scalar masses are assumed to heavy and do not play a role in our analysis. We find that this scenario is in agreement with all relevant experimental constraints, comprising the LHC searches for SUSY particles and additional Higgs bosons, the LHC Higgs-boson rate measurements, the DM direct detection limits and the upper limit on the DM relic density. We demonstrate that this scenario gives an excellent description of the observed excesses in the search for 2~and 3~soft-leptons plus \ETmiss, with $m_{\tildeχ^0_2} \sim m_{\tildeχ^0_3} \sim m_{\tildeχ^{\pm}_1}$ and $Δm_{21} \sim 20$ GeV. 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

Assessing uncertainties in the determination of the trilinear Higgs self-coupling from single-Higgs observables

Circular $e^{+}e^{-}$ colliders operating at energies below the di-Higgs production threshold can provide information on the trilinear Higgs self-coupling $λ_{hhh}$ via its loop contributions to single Higgs production processes and electroweak precision observables. We investigate how well a non-SM value of $λ_{hhh}$ can be determined indirectly via its loop contributions within a global EFT fit. Using an inert doublet extension of the SM Higgs sector as an example for a scenario of physics beyond the SM that could be realised in nature, we find that theoretical uncertainties related to the treatment of loop contributions and the truncation of the EFT expansion, which are usually neglected, play an important role in determining the sensitivity to $λ_{hhh}$ in a global fit. The results obtained from such an indirect determination of $λ_{hhh}$ without taking these additional uncertainties into account would be too optimistic, leading to an artificially high resulting precision for $λ_{hhh}$. They could therefore be misleading in the quest to precisely identify the underlying physics of electroweak symmetry breaking.

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arXiv2025

Impact of one-loop corrections to trilinear scalar couplings on di-Higgs production in the RxSM

We investigate di-Higgs production at the (HL-)LHC and possible high-energy future $e^+e^-$ colliders within the real Higgs singlet extension of the Standard Model (SM), the RxSM. This model has two CP-even Higgs bosons, $h$ and $H$, for which we assume $m_h\sim 125 \text{ GeV} < m_H$. We analyse the effect of one-loop corrections to the two trilinear scalar couplings relevant for di-Higgs production, $λ_{hhh}$ and $λ_{hhH}$, by performing an extensive parameter scan within the RxSM. We find that the one-loop corrections have a strong impact on the total production cross-sections, as well as on the differential cross-sections with respect to the invariant di-Higgs mass, $m_{hh}$. We evaluate the sensitivity of the HL-LHC and a high-energy $e^+e^-$ collider with $\sqrt{s} = 1 \text{ TeV}$, the ILC1000, to probe BSM physics effects in these processes. We demonstrate that the RxSM can be distinguished from the SM for large parts of the sampled parameter space. The resonant $H$ structure in the $m_{hh}$ distribution, on the other hand, can be observed only if the corresponding couplings, in particular $λ_{hhH}$, are sufficiently large. Here the ILC1000 yields a substantially better sensitivity than the HL-LHC.

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arXiv2025

New Physics Search at the CEPC: a General Perspective

The Circular Electron-Positron Collider (CEPC), a proposed next-generation Higgs factory, provides new opportunities to explore physics beyond the Standard Model (SM). With its clean electron-positron collision environment and the ability to collect large samples of Higgs, W, and Z bosons, the CEPC enables precision measurements and searches for new physics. This white paper outlines the CEPC's discovery potential, including studies of exotic decays of the Higgs, Z, and top quarks, dark matter and dark sector phenomena, long-lived particles, supersymmetry, and neutrino-related signatures. Advanced detector technologies and reconstruction techniques, such as one-to-one correspondence reconstruction and jet origin identification, significantly improve sensitivity to rare and weakly interacting processes. The CEPC is particularly well suited to probe the electroweak phase transition and test models of electroweak baryogenesis and dark sector interactions. In addition, global fit analyses highlight the CEPC's complementary role in constraining a wide range of new physics scenarios. These features position the CEPC as a powerful tool for exploring the next frontier in fundamental particle physics in the post-Higgs discovery era.

hep-ex↗

arXiv2025

Experimental Determination of BSM Triple Higgs Couplings at the HL-LHC with Neural Networks

The shape of the Higgs potential is modified by the presence of additional scalar fields, as predicted in many Beyond-Standard-Model (BSM) scenarios. In such cases, deviations in the Higgs self-interactions, in particular the trilinear Higgs couplings, could serve to disentangle the physics beyond the Standard Model (SM). While the SM predicts only one trilinear Higgs coupling, extended scalar sectors allow for additional self-interactions that can manifest themselves in Higgs pair production, via the $s$-channel contribution of a heavy $\mathcal{CP}$-even scalar $H$. We present the first sensitivity study to such a BSM trilinear scalar coupling using machine learning. Specifically, we train a neural network on the invariant mass distributions of Higgs pair production at the HL-LHC to extract $ξ_H^t \times λ_{hhH}$, i.e. the product of the resonant $H$ top-Yukawa coupling and the trilinear coupling of $H$ to the two SM-like Higgses in the final state, $hh$. Assuming a hypothetical $H$ mass of 450 GeV, we show that, depending on future experimental efficiencies and uncertainties, a determination of $ξ_H^t \times λ_{hhH}$ at the 10-20% level may be achievable by the end of the HL-LHC. We present a simple and more efficient alternative to classical statistical methods, proving the efficiency of neural networks for both hypothesis testing and parameter estimation, which outperforms conventional maximum likelihood methods in this context.

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arXiv2025

Towards a Refined Understanding of Non-holomorphic Soft SUSY-Breaking Effects on the Higgs Boson Mass Spectra

We study the impact of the non-holomorphic (NH) soft supersymmetry-breaking terms $ T_{33}^{\prime D} $ and $ μ^\prime $, which introduce additional SUSY-breaking effects beyond the holomorphic structure of the superpotential, on the Higgs boson mass spectrum in the NH Minimal Supersymmetric Standard Model (NHSSM). The term $ T_{33}^{\prime D} $ modifies the scalar bottom-quark mass matrix and Higgs couplings, while $ μ^\prime $ affects the mass matrices of charginos and neutralinos. In our analysis, we incorporate constraints from charge- and color-breaking (CCB) minima where we find that a portion of the parameter space is excluded by these constraints. Focusing on the allowed parameter space, the NH contributions to the light $\cal CP$-even Higgs boson mass, $ M_h $, from $ μ^\prime $ and $ T_{33}^{\prime D} $ can reach up to $ 1.4 \,\, \mathrm{GeV} $ and $ 90 \,\, \mathrm{MeV} $, respectively. For the heavy $\cal CP$-even Higgs boson mass, $ M_H $, and the charged Higgs boson mass, $ M_{H^{\pm}} $, these contributions can be substantially larger in certain regions of the parameter space, reaching up to $ 44 \,\, \mathrm{GeV} $ for $ M_H $ and $ 42 \,\, \mathrm{GeV} $ for $ M_{H^{\pm}} $ due to $ μ^\prime $, and up to $ 60 \,\, \mathrm{GeV} $ due to $ T_{33}^{\prime D} $ for both $ M_H $ and $ M_{H^{\pm}} $. These corrections are significantly larger than the expected future experimental precision for Higgs boson masses and should therefore be considered in precision analyses for future experiments.

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arXiv2025

Reinterpretation and preservation of data and analyses in HEP

Data from particle physics experiments are unique and are often the result of a very large investment of resources. Given the potential scientific impact of these data, which goes far beyond the immediate priorities of the experimental collaborations that obtain them, it is imperative that the collaborations and the wider particle physics community publish and preserve sufficient information to ensure that this impact can be realised, now and into the future. The information to be published and preserved includes the algorithms, statistical information, simulations and the recorded data. This publication and preservation requires significant resources, and should be a strategic priority with commensurate planning and resource allocation from the earliest stages of future facilities and experiments.

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arXiv2025

ALP-ine quests at the LHC: hunting axion-like particles via peaks and dips in $t \bar{t}$ production

We present an analysis of the sensitivity of current and future LHC searches for new spin-0 particles in top-anti-top-quark ($t\bar{t}$) final states, focusing on generic axion-like particles (ALPs) that are coupled to top quarks and gluons. As a first step, we derive new limits on the effective ALP Lagrangian in terms of the Wilson coefficients $c_t$ and $c_{\tilde{G}}$ based on the results of the CMS search using $35.9$ fb$^{-1}$ of data, collected at $\sqrt{s} = 13$ TeV. We then investigate how the production of an ALP with generic couplings to gluons and top quarks can be distinguished from the production of a pseudoscalar which couples to gluons exclusively via a top-quark loop. To this end, we make use of the invariant $t\bar{t}$ mass distribution and angular correlations that are sensitive to the $t\bar{t}$ spin correlation. Using a mass of 400 GeV as an example, we find that already the data collected during Run 2 and Run 3 of the LHC provides an interesting sensitivity to the underlying nature of a possible new particle. We also analyze the prospects for data anticipated to be collected during the high-luminosity phase of the LHC. Finally, we compare the limits obtained from the $t \bar t$ searches to existing experimental bounds from LHC searches for narrow di-photon resonances, from measurements of the production of four top quarks, and from global analyses of ALP-SMEFT interference effects.

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arXiv2024

Lepton Flavor Violation in Nonholomorphic Soft SUSY-Breaking Scenarios: Experimental Limits and Excesses

We investigate the prospects for the observation of lepton flavor violation (LFV) within the nonholomorphic supersymmetric standard model (NHSSM). We examine charged lepton flavor-violating (cLFV) decays such as such $μ\rightarrow e γ$, $τ\rightarrow e γ$ and $τ\rightarrow μγ$ to impose indirect constraints on both LFV holomorphic and nonholomorphic (NH) soft Supersymmetry-breaking (SSB) terms. These constraints are subsequently utilized to calculate decay rates for LFV Higgs decays (LFVHD). Within the allowed parameter space, NH contributions to LFVHD can be notably larger compared to the holomorphic counterparts. Interestingly, recently ATLAS reported an excess larger than $2\,σ$ in their searches for $h \to e τ$ and $h \to μτ$. Their best-fit point is not excluded by the corresponding CMS limits. We demonstrate that for some parts of parameter space, the predicted values for $\text{BR}(h\to e τ)$ and $\text{BR}(h\to μτ)$ in the NH scenarios reach up to the present experimental limit for these decay processes and can potentially explain the excesses observed by ATLAS, while being in agreement with other experimental constraints. If these decays are eventually observed experimentally, they could potentially serve as a distinctive signature of the NH scenarios and determine some of the NH parameters. Conversely, the limits on the LFVHDs can restrict the allowed parameter space for the NH SSB terms in the NHSSM.

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arXiv2024

Physics case for an $e^+e^-$ collider at 500 GeV and above

Some highlights of the physics case for running an $e^+e^-$ collider at 500 GeV and above are discussed with a particular emphasis on the experimental access to the Higgs potential via di-Higgs and (at sufficiently high energy) triple Higgs production. The information obtainable from Higgs pair production at about 500 GeV is compared with the prospects for the HL-LHC and with the indirect information that can be obtained from a Higgs factory running at lower energies.

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arXiv2024

A 95 GeV Higgs Boson in the Georgi-Machacek Model

CMS and ATLAS have reported small excesses in the search for low-mass Higgs bosons in the di-photon decay channel at exactly the same mass, $95.4~$GeV. These searches rely on improved analysis techniques, enhancing in particular the discrimination against the $Z \to e^+e^-$ background. In models beyond the Standard Model (SM) that extend the Higgs sector with triplets, doubly-charged Higgs bosons are predicted which can contribute substantially to the di-photon decay rate of a light Higgs boson. The Georgi-Machacek (GM) Model is of particular interest in this context, since despite containing Higgs triplets it preserves the electroweak $ρ$-parameter to be$~$1 at the tree level. We show that within the GM model, a Higgs boson with a mass of $\sim 95~$GeV with a di-photon decay rate as observed by CMS and ATLAS can be well described. 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 have been found at comparable masses with local significances of about $2σ$ and $3σ$, respectively. The presence of a Higgs boson at about $95~$GeV within the GM model would imply good prospects of the searches for additional light Higgs bosons. In particular, the observed excess in the di-photon channel would be expected to be correlated in the GM model with a light doubly-charged Higgs boson in the mass range between $100~$GeV and $200~$GeV, which motivates dedicated searches in upcoming LHC Runs.

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arXiv2024

$(g-2)_μ$ and Stau coannihilation : Dark Matter and Collider Analysis

Slepton coannihilation is one of the most promising scenarios that can bring the predicted Dark Matter (DM) abundance in the the Minimal Supersymmetric Standard Model (MSSM) into agreement with the experimental observation. In this scenario, the lightest supersymmetric particle (LSP), usually assumed to be the lightest neutralino, can serve as a Dark Matter (DM) candidate while the sleptons as the next-to-LSPs (NLSPs) lie close in mass. In our previous studies analyzing the electroweak (EW) sector of MSSM, a degeneracy between the three generations of sleptons was assumed for the sake of simplicity. In case of slepton coannihilation this directly links the smuons involved in the explanation for $(g-2)_μ$ to the coannihilating NLSPs required to explain the DM content of the universe. On the other hand, in well-motivated top-down models such degeneracy does not hold, and often the lighter stau turns out to be the NLSP at the EW scale, with the smuons (and selectrons) somewhat heavier. In this paper we analyze a non-universal slepton mass scenario at the EW scale where the first two generations of sleptons are taken to be mass-degenerate and heavier than the staus, enforcing stau coannihilation. We analyze the parameter space of the MSSM in the light of a variety of experimental data namely, the DM relic density and direct detection (DD) limits, LHC data and especially, the discrepancy between the experimental result for $(g-2)_μ$, and its Standard Model (SM) prediction. We find an upper limit on the LSP and NLSP masses of about ~ 550 GeV. In contrast to the scenario with full degeneracy among the three families of sleptons, the upper limit on the light smuon/selectron mass moves up by ~ 200 GeV. We analyze the DD prospects as well as the physics potential of the HL-LHC and a future high-energy $e^+ e^-$ collider to investigate this scenario further.

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arXiv2024

Consistent Excesses in the Search for $\tilde χ_2^{\rm 0} \tilde χ_1^{\rm \pm}$ : Wino/bino vs. Higgsino Dark Matter

The quest for supersymmetric (SUSY) particles is among the main search channels currently pursued at the LHC. Particularly, electroweak (EW) particles with masses as low as a few hundred GeV are still viable. Recent searches for the ``golden channel'', $pp \to \tilde χ_2^{\rm 0} \tilde χ_1^{\rm \pm} \to \tilde χ_1^{\rm 0} Z^{(*)} \, \tilde χ_1^{\rm 0} W^{\pm (*)}$ show consistent excesses between ATLAS and CMS in the 2~lepton, 3-lepton and mono-jet searches, assuming $m_{\tilde χ_2^{\rm 0}} \approx m_{\tilde χ_1^{\rm \pm}} \gtrsim 200$ GeV and $Δm := m_{\tilde χ_2^{\rm 0}} - m_{\tilde χ_1^{\rm 0}} \approx 20$ GeV. This mass configuration arises naturally in SUSY scenarios with wino/bino Dark Matter (DM) or higgsino DM. In these scenarios the lightest supersymmetric particle (LSP), assumed to be the lightest neutralino, as a DM candidate, is in good agreement with the observed limits on the DM content of the universe, as well as with negative results from Direct Detection (DD) experiments. We analyze these two scenarios with respect to the observed excesses, taking into account all relevant experimental constraints. We show that in particular wino/bino DM with different signs of the $SU(2)$ and $U(1)$ soft SUSY-breaking parameters can describe well the experimental excesses, while being in agreement with all other constraints.

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