arXiv subjects

M. Mühlleitner

Publications and source records attributed to M. Mühlleitner.

At least 19 recordsLinked to original sources

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

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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arXiv2023

Full NLO QCD predictions for Higgs-pair production in the 2-Higgs-Doublet Model

After the discovery of the Higgs boson in 2012 at the CERN Large Hadron Collider (LHC), the study of its properties still leaves room for an extended Higgs sector with more than one Higgs boson. 2-Higgs Doublet Models (2HDMs) are well-motivated extensions of the Standard Model (SM) with five physical Higgs bosons: two CP-even states $h$ and $H$, one CP-odd state $A$, and two charged states $H^\pm_{}$. In this letter, we present the calculation of the full next-to-leading order (NLO) QCD corrections to $hH$ and $AA$ production at the LHC in the 2HDM at small values of the ratio of the vacuum expectation values, $\tanβ$, including the exact top-mass dependence everywhere in the calculation. Using techniques applied in the NLO QCD SM Higgs pair production calculation, we present results for the total cross section as well as for the invariant Higgs-pair-mass distribution at the LHC. We also provide the top-quark scale and scheme uncertainties which are found to be sizeable.

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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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arXiv2021

The CN2HDM

We present the CP-violating Next-to-2-Higgs-Doublet Model (CN2HDM) which is based on the extension of the CP-violating 2-Higgs-Doublet-Model (C2HDM) by a complex singlet field that obeys a discrete $\mathbb{Z}_2$ symmetry. The model thus features not only CP violation required for successful electroweak baryogenesis but also a Dark Matter (DM) candidate. The model has an extended Higgs sector with four CP-mixing visible neutral Higgs bosons, a DM candidate and a pair of oppositely charged Higgs bosons. The possibility of singlet and CP-odd admixtures to the observed Higgs boson in addition to the large number of visible scalar particles leads to an interesting Higgs phenomenology. We find that the model can easily provide 100\% of the DM relic density and investigate interesting LHC and DM observables within the model. We provide all the tools necessary to study the CN2HDM in detail and point out future research directions for this interesting benchmark model that can address some of the most pressing open questions of the Standard Model.

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arXiv2021

$gg\to HH$: Combined Uncertainties

In this note we discuss the combination of the usual renormalization and factorization scale uncertainties of Higgs-pair production via gluon fusion with the novel uncertainties originating from the scheme and scale choice of the virtual top mass. Moreover, we address the uncertainties related to the top-mass definition for different values of the trilinear Higgs coupling and their combination with the other uncertainties.

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arXiv2020

Higgs boson potential at colliders: status and perspectives

This document summarises the current theoretical and experimental status of the di-Higgs boson production searches, and of the direct and indirect constraints on the Higgs boson self-coupling, with the wish to serve as a useful guide for the next years. The document discusses the theoretical status, including state-of-the-art predictions for di-Higgs cross sections, developments on the effective field theory approach, and studies on specific new physics scenarios that can show up in the di-Higgs final state. The status of di-Higgs searches and the direct and indirect constraints on the Higgs self-coupling at the LHC are presented, with an overview of the relevant experimental techniques, and covering all the variety of relevant signatures. Finally, the capabilities of future colliders in determining the Higgs self-coupling are addressed, comparing the projected precision that can be obtained in such facilities. The work has started as the proceedings of the Di-Higgs workshop at Colliders, held at Fermilab from the 4th to the 9th of September 2018, but it went beyond the topics discussed at that workshop and included further developments.

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arXiv2019

Electroweak Phase Transition in Non-Minimal Higgs Sectors

Higgs sector extensions beyond the Standard Model (BSM) provide additional sources of CP violation and further scalar states that help to trigger a strong first order electroweak phase transition (SFOEWPT) required to generate the observed baryon asymmetry of the Universe through electroweak baryogenesis. We investigate the CP-violating 2-Higgs-Doublet Model (C2HDM) and the Next-to-Minimal 2-Higgs-Doublet Model (N2HDM) with respect to their potential to generate an SFOEWPT while being compatible with all relevant and recent theoretical and experimental constraints. The implications of an SFOEWPT on the collider phenomenology of the two models are analysed in detail in particular with respect to Higgs pair production. We provide benchmark points for parameter points that are compatible with an SFOEWPT and provide distinct di-Higgs signatures.

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arXiv2019

Electroweak Corrections to Dark Matter Direct Detection in a Vector Dark Matter Model

Although many astrophysical and cosmological observations point towards the existence of Dark Matter (DM), the nature of the DM particle has not been clarified to date. In this paper, we investigate a minimal model with a vector DM (VDM) candidate. Within this model, we compute the cross section for the scattering of the VDM particle with a nucleon. We provide the next-to-leading order (NLO) cross section for the direct detection of the DM particle. Subsequently, we study the phenomenological implications of the NLO corrections, in particular with respect to the sensitivity of the direct detection DM experiments. We further investigate more theoretical questions such as the gauge dependence of the results and the remaining theoretical uncertainties due to the applied approximations.

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arXiv2019

ewN2HDECAY - A program for the Calculation of Electroweak One-Loop Corrections to Higgs Decays in the Next-to-Minimal Two-Higgs-Doublet Model Including State-of-the-Art QCD Corrections

We present in this paper our new program package ewN2HDECAY for the calculation of the partial decay widths and branching ratios of the Higgs bosons of the Next-to-Minimal 2-Higgs Doublet Model (N2HDM). The N2HDM is based on a general CP-conserving 2HDM which is extended by a real scalar singlet field. The program computes the complete electroweak one-loop corrections to all non-loop-induced two-body on-shell Higgs boson decays in the N2HDM and combines them with the state-of-the-art QCD corrections that are already implemented in the existing program N2HDECAY. Most of the independent input parameters of the electroweak sector of the N2HDM are renormalized in an on-shell scheme. The soft-$\mathbb{Z}_2$-breaking squared mass scale $m_{12}^2$ and the vacuum expectation value $v_S$ of the $SU(2)_L$ singlet field, however, are renormalized with $\overline{\text{MS}}$ conditions, while for the four scalar mixing angles $α_i$ ($i=1,2,3$) and $β$ of the N2HDM, several different renormalization schemes are applied. By giving out the leading-order and the loop-corrected partial decay widths separately from the branching ratios, the program ewN2HDECAY not only allows for phenomenological analyses of the N2HDM at highest precision, it can also be used for a study of the impact of the electroweak corrections and the remaining theoretical uncertainty due to missing higher-order corrections based on a change of the renormalization scheme. The input parameters are then consistently calculated with a parameter conversion routine when switching from one renormalization scheme to the other. The latest version of the program ewN2HDECAY can be downloaded from the URL \href{https://github.com/marcel-krause/ewN2HDECAY}{https://github.com/marcel-krause/ewN2HDECAY}.

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arXiv2019

Two-Loop ${\cal O}(α_t^2)$ Corrections to the Neutral Higgs Boson Masses in the CP-Violating NMSSM

We present our calculation of the two-loop corrections of ${\cal O}(α_t^2)$ to the neutral Higgs boson masses of the CP-violating Next-to-Minimal Supersymmetric extension of the Standard Model (NMSSM). The calculation is performed in the Feynman diagrammatic approach in the gaugeless limit at vanishing external momentum. We apply a mixed $\overline{\mathrm{DR}}$-on-shell (OS) renormalization scheme for the NMSSM input parameters. Furthermore, we exploit a $\overline{\mathrm{DR}}$ as well as an OS renormalization in the top/stop sector. The corrections are implemented in the Fortran code NMSSMCALC for the calculation of the Higgs spectrum both in the CP-conserving and CP-violating NMSSM. The code also provides the Higgs boson decays including the state-of-the-art higher-order corrections. The corrections computed in this work improve the already available corrections in NMSSMCALC which are the full one-loop corrections without any approximation and the two-loop ${\cal O}(α_t α_s)$ corrections in the gaugeless limit and at vanishing external momentum. Depending on the chosen parameter point, we find that the ${\cal O}(α_t α_s + α_t^2)$ corrections add about 4-7% to the one-loop mass of the SM-like Higgs boson for $\overline{\mathrm{DR}}$ renormalization in the top/stop sector and they reduce the mass by about 6-9% if OS renormalization is applied. For an estimate of the theoretical uncertainty we vary the renormalization scale and change the renormalization scheme and show that care has to be taken in the corresponding interpretation.

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arXiv2019

The CLIC Potential for New Physics

The Compact Linear Collider (CLIC) is a mature option for the future of high energy physics. It combines the benefits of the clean environment of $e^+e^-$ colliders with operation at high centre-of-mass energies, allowing to probe scales beyond the reach of the Large Hadron Collider (LHC) for many scenarios of new physics. This places the CLIC project at a privileged spot in between the precision and energy frontiers, with capabilities that will significantly extend knowledge on both fronts at the end of the LHC era. In this report we review and revisit the potential of CLIC to search, directly and indirectly, for physics beyond the Standard Model.

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arXiv2018

Les Houches 2017: Physics at TeV Colliders New Physics Working Group Report

We present the activities of the `New Physics' working group for the `Physics at TeV Colliders' workshop (Les Houches, France, 5--23 June, 2017). Our report includes new physics studies connected with the Higgs boson and its properties, direct search strategies, reinterpretation of the LHC results in the building of viable models and new computational tool developments.

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arXiv2016

Les Houches 2015: Physics at TeV colliders - new physics working group report

We present the activities of the 'New Physics' working group for the 'Physics at TeV Colliders' workshop (Les Houches, France, 1-19 June, 2015). Our report includes new physics studies connected with the Higgs boson and its properties, direct search strategies, reinterpretation of the LHC results in the building of viable models and new computational tool developments. Important signatures for searches for natural new physics at the LHC and new assessments of the interplay between direct dark matter searches and the LHC are also considered.

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arXiv2014

Interim recommendations for the evaluation of Higgs production cross sections and branching ratios at the LHC in the Two-Higgs-Doublet Model

In this note we give interim recommendations on how to evaluate LHC cross sections for (neutral) Higgs production and Higgs branching ratios in the general (CP-conserving) Two-Higgs-Doublet Model (2HDM). The current status of available higher-order corrections to Higgs production and decay in this model is discussed, and the existing public codes implementing these calculations are described. Numerical results are presented for a set of reference scenarios, demonstrating the very good agreement between the results obtained using different programs.

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arXiv2011

Handbook of LHC Higgs Cross Sections: 1. Inclusive Observables

This Report summarizes the results of the first 10 months' activities of the LHC Higgs Cross Sections Working Group. The main goal of the working group was to present the status-of-art on Higgs Physics at the LHC integrating all new results that have appeared in the last few years. The Report is more than a mere collection of the proceedings of the general meetings. The subgroups have been working in different directions. An attempt has been made to present the first Report from these subgroups in a complete and homogeneous form. The subgroups' contributions correspondingly comprise the main parts of the Report. A significant amount of work has been performed in providing higher-order corrections to the Higgs-boson cross sections and pinning down the theoretical uncertainty of the Standard Model predictions. This Report comprises explicit numerical results on total cross sections, leaving the issues of event selection cuts and differential distributions to future publications. The subjects for further study are identified.

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