arXiv subjects

Margarete Mühlleitner

Publications and source records attributed to Margarete Mühlleitner.

At least 19 recordsLinked to original sources

arXiv2026

Z and Higgs Factory Implications of Two Higgs Doublets with First-Order Phase Transitions

We investigate the potential of future electron-positron colliders, such as FCC-ee and CEPC, to probe 2-Higgs-doublet models (2HDMs) that facilitate a strong first-order electroweak phase transition (SFOEWPT), a necessary condition for electroweak baryogenesis. Focusing on a 2HDM in the CP-conserving limit, we identify parameter regions consistent with an SFOEWPT and evaluate their compatibility with projected precision electroweak and Higgs measurements, as well as searches for exotic Higgs bosons. We show that radiative corrections to $e^+e^-\to hZ$ production introduce deviations in the cross section that are resolvable with the anticipated sub-percent precision at lepton colliders even when experimental outcomes of the LHC and $Z$ pole measurements are in agreement with the SM. This underscores the opportunities of a precision lepton collider to explore BSM quantum corrections to the Higgs sector more broadly.

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arXiv2026

Higgs Boson Pair Production via Gluon Fusion: Higher-Order Corrections and Theoretical Uncertainties

In this contribution, the higher-order QCD and electroweak corrections to Standard Model Higgs boson pair production via the gluon-fusion mechanism, $gg\to hh$, are summarized and the different sources of theoretical uncertainty are assessed. The discussion includes finite top quark mass effects, matching to parton showers, approximate NNLO and N$^3$LO QCD corrections, NLO electroweak effects, and uncertainties associated with the top quark mass scheme and perturbative scale choices. In addition, we provide an updated state-of-the-art recommendation for the inclusive gluon-fusion Higgs boson pair production cross section and the corresponding Higgs boson pair invariant-mass distribution.

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arXiv2026

Exploring Extended Higgs Dynamics via Higgsstrahlung at FCC-ee

The Future Circular Electron-Positron Collider (FCC-ee) will probe aspects of the Higgs boson and the electroweak scale with unprecedented precision via associated Higgs production with a $Z$ boson. We focus on the Two-Higgs-Doublet Model (2HDM) to frame the FCC-ee's precision constraints within a small, concrete parameter space at next-to-leading order. We demonstrate that the projected precision of the FCC-ee's 240 GeV run will enable a precise analysis of Beyond-the-Standard-Model (BSM)-relevant Higgs-sector interactions near the alignment limit. As the key aspects of the 2HDM that drive deviations of the cross section from its Standard Model expectation (presence of new scalar states, Higgs mixing, and non-trivial inter-Higgs couplings) are also typically present in extensions more complex than the 2HDM, this demonstrates the FCC-ee's indirect potential for unveiling BSM physics around the electroweak scale.

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arXiv2026

A Comprehensive Analysis of the R2HDM Vacuum Evolution and the Induced GW and Collider Phenomenology

Extended Higgs sectors beyond the Standard Model (BSM) allow to dynamically generate the observed baryon asymmetry of the Universe through electroweak baryogenesis and thereby solve one of the most prominent open problems of the SM. The strong first-order phase transitions (PTs), required to preserve the generated asymmetry in the electroweak vacuum, source gravitational waves (GW) that can be tested at future experiments like LISA. Gravitational waves hence provide the exciting possibility to probe BSM physics through cosmological processes. In order to be able to eventually pin down the specific underlying physics, a good understanding of the evolution of the vacuum of the model under investigation is indispensable as well as of the uncertainties that are involved in the derivation of the GW spectrum. We use our code BSMPTv3 that allows to reliably derive the finite temperature vacuum structure of extended Higgs sectors with multiple vacuum directions and calculates the GW spectrum of the found (multiple) strong first-order PTs, and we apply it to the real, i.e. CP-conserving, 2-Higgs-Doublet Model. Taking into account all relevant theoretical and experimental constraints, we perform a thorough analysis of its vacuum evolution, the related collider and GW phenomenology and complement it by an uncertainty discussion.

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arXiv2026

Full Next-To Leading-Order Electroweak and QCD Corrections to the Relic Density in the CxSM

In this work, we present the calculation of the next-to-leading order (NLO) QCD and electroweak corrections to the thermally averaged cross section of Dark Matter (DM) annihilation in the framework of the complex singlet extended Standard Model (CxSM) with one DM candidate. We derive the corresponding NLO QCD and electroweak corrected relic density and discuss the impact of the corrections as well as the remaining theoretical uncertainty due to missing higher-order corrections. This is estimated through a variation of the renormalization schemes for the singlet vacuum expectation value $v_S$ and the Higgs mixing angle $α$. For the bulk of the scanned parameter points, the QCD and electroweak corrections are found to be of typical size with the remaining theoretical uncertainty ranging at the percent level. The larger corrections that are found, can be attributed to a large counterterm for $v_S$ emerging in the case of large mass gaps in the decay channel used for the renormalization. The corrections are of phenomenological impact. There are parameter points that are allowed at leading order (LO), but are excluded after including the NLO corrections to the relic density, and vice versa. Our corrections have been implemented in the new code RelExt@NLO based on the LO code RelExt, which has been made publicly available. This work marks a first step towards the calculation of the QCD and electroweak corrected relic densities in models with DM candidates stabilized by a discrete $\mathbb{Z}_2$ symmetry.

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arXiv2026

A Deep Dive into Baryon Asymmetry -- the C2HDM

In this paper, we present our new implementation of the computation of the baryon asymmetry in the code BSMPT. It is based on the WKB ansatz generalizing the transport equations to an arbitrary number of moments. Two different truncation schemes are implemented, and the profile of the vacuum expectation value (VEV) is derived from the equations of motion in addition to the modeling with the kink profile. We validate our implementation with a simple benchmark model and perform a detailed analysis within the CP-violating 2-Higgs-Doublet Model (C2HDM). Barring the collision term, however, our implementation can readily be applied to any extended Higgs sector with an arbitrary number of VEV directions. We study in detail the dependencies of the baryon asymmetry on the number of moment equations, the applied truncation scheme, the wall velocity, the wall velocity times wall width, the VEV profile, the strength of the phase transition, and the amount of CP violation in the model and present a detailed uncertainty analysis. We investigate the interplay of the generated baryon asymmetry and the gravitational waves signal at LISA. Our results guide the way for future improvements in the computation of the baryon asymmetry and give directions for model building. The uncertainty analysis is the basis for any investigation aiming at deducing model parameters from cosmological processes.

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arXiv2026

Dark Matter in Multi-Singlet Extensions of the Standard Model

We study the simplest extensions of the Standard Model (SM) that provide Dark Matter (DM) candidates, built with the addition of real singlets and new $\mathcal{Z}_2$ symmetries. In this type of models the interactions between SM particles are not altered except for the new interactions stemming from the portal couplings that link the SM Higgs with the DM candidates. In the extension with just one singlet, DM masses below about 3.5 TeV are already excluded by the combination of relic density and direct detection (DD) constraints, except in the resonant case where the DM mass is close to half the Higgs mass, making them undetectable at the LHC. Adding just one more real singlet with an independent $\mathcal{Z}_2$ symmetry opens up a new mass window for one of the DM candidates and decreases the lower bound on the mass of the other. Adding more singlets with independent $\mathcal{Z}_2$ symmetries will not change this picture dramatically. If instead we add new singlets all odd under the same $\mathcal{Z}_2$ symmetry, the allowed mass region for the DM candidate (i.e., the lightest dark sector scalar) will span the entire mass range from half the Higgs mass to the TeV scale. In principle, such light particles could be probed at the LHC in mono-$X$ searches. Although they are still out of reach with the current LHC DM searches, there are good chances to probe the models in some final states at the High-Luminosity (HL-LHC) stage of the LHC.

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arXiv2026

Phenomenology of a Kinetic Higgs Portal

We explore the phenomenological consequences of non-minimal hidden sector interactions on observable correlations in the Higgs sector, mediated through the $\mathbb{Z}_2$-symmetric Higgs portal. Particular attention is given to non-standard momentum dependencies of the hidden sector scalar, which arise naturally in an effective field theory (EFT) framework, e.g. in Composite Scalar Dark Matter theories. We discuss the implications of such hidden sector interactions for the thermal history of the universe. We show that aspects of such non-standard momentum dependencies can be probed at future lepton colliders such as a FCC-ee, potentially also through radiative corrections. This gives rise to precision probes for regions where direct detection constraints and relic abundance can be accounted for as predicted in, e.g., Composite Scalar Dark Matter theories.

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arXiv2026

NMSSMScanner: Efficient Scans in the NMSSM Parameter Space Proof of Concept

We present the first version of the new scanning tool NMSSMScanner that allows to perform efficient scans in the complex multi-parameter space of the Next-to-Minimal Supersymmetric extension of the Standard Model (NMSSM) while taking into account all relevant constraints. As a proof of concept we apply it to the search for NMSSM parameter configurations that maximize Higgs boson pair production from resonant scalar or pseudoscalar production in various final states.

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arXiv2026

Reassessing CP Violation in the C2HDM with Machine Learning

We provide a study of the parameter space of the complex 2-Higgs Doublet Model (C2HDM), focusing on signs of large CP-violating couplings of the 125 GeV Higgs boson with the fermions. The study is performed utilizing Machine Learning (ML) techniques developed recently for parameter space exploration, including an Evolutionary Strategy Algorithm and Novelty Reward. We give particular attention to the electron electric dipole moment (eEDM). We confirm that the recently found kite diagrams are crucial for the outcome of the analysis. Moreover, their use also mitigates the dependence of the results on the scale and scheme choice of the masses in the loop diagrams. We furthermore point out that, already at the current level of experimental precision, the Barr-Zee diagrams with charm quark loops must be taken into account. The combined use of kite diagrams and ML techniques allows for the resurrection of large fermion CP-odd couplings for Type-II and Flipped C2HDM when the 125 GeV Higgs coincides with the second lightest neutral scalar. This arises due to cancellations, typically of the per-mil order, which, moreover, will still be possible for a foreseeable eEDM precision down to $10^{-33}$ e.cm. For these cases, the constraints on the CP-odd couplings arises from the precision LHC measurements.

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arXiv2025

Higgs-Pair Production via Gluon Fusion: Top-Yukawa- and light-quark-induced electroweak Corrections

Gluon fusion, $gg\to HH$, is the dominant Higgs-pair production process at the Large Hadron Collider (LHC) and provides the first direct access to the trilinear Higgs self-interaction. The process is loop-induced, with the main contribution emerging from top-quark loops within the Standard Model. In the past, the QCD corrections have been calculated and found to increase the cross section significantly. With the anticipated accuracies achievable at the high-luminosity LHC (HL--LHC), the theoretical uncertainties will be of increased relevance to compete with the experimental precision at the level of less than 30\%. In this work, we take the next steps towards the determination of the complete electroweak corrections at next-to-leading order by calculating the full top-Yukawa and light-quark induced corrections. These corrections modify the cross section moderately in the kinematical regimes of interest.

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arXiv2025

BSMPT v3 A Tool for Phase Transitions and Primordial Gravitational Waves in Extended Higgs Sectors

Strong first-order phase transitions (SFOPT) during the evolution of the Higgs potential in the early universe not only allow for the dynamical generation of the observed matter-antimatter asymmetry, they can also source a stochastic gravitational wave (GW) background possibly detectable with future space-based GW interferometers. As SFOPTs are phenomenologically incompatible with the Standard Model (SM) Higgs sector, the observation of GWs from SFOPTs provides an exciting interplay between cosmology and particle physics in the search for new physics. With the C++ code BSMPTv3, we present for the first time a tool that performs the whole chain from the particle physics model to the GW spectrum. Extending the previous versions BSMPTv1 and v2, it traces the phases of beyond-SM (BSM) Higgs potentials and is capable of treating multiple vacuum directions and multi-step phase transitions. During the tracing, it checks for discrete symmetries, flat directions, and electroweak symmetry restoration, and finally reports the transition history. The transition probability from the false to the true vacuum is obtained from the solution of the bounce equation which allows for the calculation of the nucleation, percolation and completion temperatures. The amplitude and characteristic frequencies of the GWs originating from bubble collisions and highly relativistic fluid shells, sound waves and turbulence, are evaluated after the calculation of the thermal parameters at the transition temperature, and finally the signal-to-noise ratio at LISA is provided. The code BSMPTv3 is a powerful self-contained tool that comes more than timely and will be of great benefit for investigations of the vacuum structure of the early universe of not only simple but also complicated Higgs potentials involving several vacuum directions, with exciting applications in the search for new physics.

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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

Loop-corrected Trilinear Higgs Self-Couplings in the NMSSM with Inverse Seesaw Mechanism

The higher-order corrections for the SM-like Higgs boson mass and the trilinear Higgs self-couplings in the Next-to-Minimal Supersymmetric extension of the Standard Model (NMSSM) with Inverse Seesaw Mechanism are significant and highly correlated. We present here the full one-loop corrections to the trilinear Higgs self-couplings supplemented by the dominant top-Yukawa and strong coupling induced two-loop corrections from our previous calculations in the complex NMSSM. These corrections are performed consistently with the corresponding Higgs boson mass corrections. We discuss in detail the new effects from the extended neutrino and sneutrino sectors on both the trilinear Higgs self-couplings and the SM-like Higgs boson mass. When compared to the case of the NMSSM without Inverse Seesaw Mechanism, the new effects can be up to 10\% for the effective SM-like trilinear Higgs self-couplings, and up to 4.5\% for the SM-like Higgs boson mass for valid parameter points, i.e. points satisfying the Higgs data, the neutrino data, the constraints from the charged lepton flavor-violating decays, and the new physics constraints from the oblique parameters $S, T, U$. The new corrections are also included in the Higgs-to-Higgs decays for the heavy Higgs states and implemented in the new version of the Fortran code NMSSMCALC-nuSS.

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arXiv2025

A Global View of the EDM Landscape

Permanent electric dipole moments (EDMs) are sensitive probes of the symmetry structure of elementary particles, which in turn is closely tied to the baryon asymmetry in the universe. A meaningful interpretation framework for EDM measurements has to be based on effective quantum field theory. We interpret the measurements performed to date in terms of a hadronic-scale Lagrangian, using the SFitter global analysis framework. We find that part of this Lagrangian is constrained very well, while some of the parameters suffer from too few high-precision measurements. Theory uncertainties lead to weaker model constraints, but can be controlled within the global analysis.

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arXiv2025

Distorting the Top Resonance with Effective Interactions

Interference effects in effective field theory (EFT) analyses can significantly distort sensitivity expectations, leaving subtle yet distinct signatures in the reconstruction of final states crucial for limit setting around Standard Model predictions. Using the specific example of four-fermion operators in top-quark pair production at the LHC, we provide a detailed quantitative assessment of these resonance distortions. We explore how continuum four-fermion interactions affect the resonance shapes, creating potential tensions between the high-statistics resonance regions and rare, high momentum-transfer continuum excesses. Our findings indicate that although four-fermion interactions do modify the on-shell region comparably to continuum enhancements, current experimental strategies at the High-Luminosity LHC are unlikely to capture these subtle interference-induced distortions. Nonetheless, such effects could become critical for precision analyses at future lepton colliders, such as the FCC-ee. Our work underscores the importance of resonance-shape measurements as complementary probes in global EFT approaches, guiding robust and self-consistent experimental strategies in ongoing and future high-energy physics programmes.

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arXiv2025

Higgs Mass Predictions in the CP-Violating High-Scale NMSSM

In a supersymmetric theory, large mass hierarchies can lead to large uncertainties in fixed-order calculations of the Standard Model (SM)-like Higgs mass. A reliable prediction is then obtained by performing the calculation in an effective field theory (EFT) framework, involving a matching to the full supersymmetric theory at the high scale to include contributions from the heavy particles, and a subsequent renormalisation-group running down to the low scale. We report on the prediction of the SM-like Higgs mass within the CP-violating Next-to-Minimal Supersymmetric extension of the SM (NMSSM) in a scenario where all non-SM particles feature TeV-scale masses. The matching conditions are calculated at full one-loop order using two approaches. These are the matching of the quartic Higgs couplings as well as of the SM-like Higgs pole masses of the low- and high-scale theory. A comparison between the two methods allows us to estimate the size of terms suppressed by the heavy mass scale that are neglected in a pure EFT calculation as given by the quartic-coupling matching. Furthermore, we study the different sources of uncertainty which enter our calculation as well as the effect of CP-violating phases on the Higgs mass prediction. The matching calculation is implemented in a new version of the public program package NMSSMCALC.

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arXiv2024

Double and Triple Higgs Production to probe the Electroweak Phase Transition

The production of three Higgs bosons could be a stretch goal for the LHC and a strategic case for future colliders. In this work, we analyse the phenomenological prospects of (neutral) triple Higgs compared to di-Higgs boson production, for a range of Higgs-sector extensions from a strong first-order electroweak phase transition perspective. In parallel, we include constraints from existing exotics and Higgs boson measurements that further limit the parameter space of such models. Resonance contributions offer large modifications in particular for triple Higgs production, albeit starting from a small SM expectation. With enhancements of order 40 over the SM, however, experimental efforts to obtain limits at the HL-LHC are well-motivated and well-placed. This is further highlighted by the potential of these processes to inform the investigation of the thermal history of our universe.

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