arXiv subjects

Margarete Mühlleitner

Publications and source records attributed to Margarete Mühlleitner.

At least 37 records · Page 2Linked to original sources

arXiv2024

Composite 2-Higgs Doublet Model: Strong Effects on Higgs Pair Production

We show how effects of compositeness emerging in a Composite 2-Higgs Doublet Model can enter Standard Model (SM)-like Higgs pair production at the Large Hadron Collider in both resonant and non-resonant mode. Such effects can arise from modified trilinear Higgs self-couplings and top-Yukawa couplings as well as from loops of new heavy quarks and additional quartic Higgs-fermion interactions. In the resonant case, significant distortions of the Breit- Wigner shape of a new scalar state decaying into the two SM-like Higgs states may occur due to interference effects amongst not only the SM-like diagrams but also those involving the new heavy quarks. In the non-resonant case, a modification of the underlying line-shape and a local maximum at twice a new heavy quark mass appear simultaneously. We quantify these effects by taking into account the relevant theoretical and latest experimental bounds.

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arXiv2024

Impact of New Experimental Data on the C2HDM: the Strong Interdependence between LHC Higgs Data and the Electron EDM

The complex two-Higgs doublet model (C2HDM) is one of the simplest extensions of the Standard Model with a source of CP-violation in the scalar sector. It has a $\mathbb{Z}_2$ symmetry, softly broken by a complex coefficient. There are four ways to implement this symmetry in the fermion sector, leading to models known as Type-I, Type-II, Lepton-Specific and Flipped. In the latter three models, there is a priori the surprising possibility that the 125 GeV Higgs boson couples mostly as a scalar to top quarks, while it couples mostly as a pseudoscalar to bottom quarks. This ``maximal'' scenario was still possible with the data available in 2017. Since then, there have been more data on the 125 GeV Higgs boson, direct searches for CP-violation in angular correlations of $τ$-leptons produced in Higgs boson decays, new results on the electron electric dipole moment, new constraints from LHC searches for additional Higgs bosons and new results on $b\to s γ$ transitions. Highlighting the crucial importance of the physics results of LHC's Run 2, we combine all these experiments and show that the ``maximal'' scenario is now excluded in all models. Still, one can have a pseudoscalar component in $h τ\barτ$ couplings in the Lepton-Specific case as large as $87\%$ of the scalar component for all mass orderings of the neutral scalar bosons.

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arXiv2024

Freeze-in as a Complementary Process to Freeze-Out

There are many extensions of the Standard Model with a dark matter (DM) candidate obtained via the freeze-out mechanism. It can happen that after all experimental and theoretical constraints are taken into account, all parameter points have a relic density below the experimentally measured value. This means that the models solve only partially the DM problem, and at least one more candidate is needed. In this work we show that it is possible to further extend the model with a DM candidate obtained via the freeze-in mechanism to be in agreement with the relic density experimental measurement. Once the relic density problem is solved with this addition, new questions are raised. This new model with at least two DM candidates could have a freeze-out undetectable DM particle both in direct and indirect detection. This could happen if the freeze-out DM particle would have a very low density. Hence, a collider DM hint via excess in the missing energy with no correspondence in direct and indirect detection experiments, could signal the existence of a Feebly Interacting Massive Particle (FIMP). Conversely, if a DM particle is found and a particular model can explain all observables except the correct relic density, an extension with an extra FIMP would solve the problem. The freeze-in DM candidate, due to the small portal couplings, will not change the remaining phenomenology.

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arXiv2024

Intermediate Charge-Breaking Phases and Symmetry Non-Restoration in the 2-Higgs-Doublet Model

The Higgs potentials of extended Higgs sectors exhibit a complex and interesting vacuum structure. When travelling back in time, i.e. going to higher temperatures, the structure may change and exhibit interesting phase patterns and sequences of phases related to the respective minima of the potential. The investigation of the vacuum structure can give us indirect insights in beyond-Standard-Model physics and the evolution of the Universe. In this paper, we investigate the possibility of an intermediate charge-breaking (CB) phase in the 2-Higgs-Doublet Model (2HDM) type I. The existence has been reported previously by using a simple potential setup. We here confirm that the intermediate CB phase can still exist when using the one-loop corrected effective potential including thermal masses. We discuss its features and the relation with SU(2) symmetry (non-)restoration as well as its consistency with the current experimental data. Lastly, we show for some selected benchmark points the rich and interesting phase patterns and sequences that the 2HDM can undergo during its evolution from the early Universe to today's electroweak vacuum.

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arXiv2023

Effective 2HDM Yukawa Interactions and a Strong First-Order Electroweak Phase Transition

The top quark as the heaviest particle in the Standard Model (SM) defines an important mass scale for Higgs physics and the electroweak scale itself. It is therefore a well-motivated degree of freedom which could reveal the presence of new interactions beyond the SM. Correlating modifications of the top-Higgs interactions in the 2-Higgs-Doublet Model (2HDM), we analyse effective field theory deformations of these interactions from the point of view of a strong first-order electroweak phase transition (SFOEWPT). We show that such modifications are compatible with current Higgs data and that an SFOEWPT can be tantamount to a current overestimate of exotic Higgs searches' sensitivity at the LHC in $t\bar t$ and four top quark final states. We argue that these searches remain robust from the point of accidental signal-background interference so that the current experimental strategy might well lead to 2HDM-like discoveries in the near future.

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arXiv2023

Dark Coloured Scalars Impact on Single and Di-Higgs Production at the LHC

The search for Dark Matter (DM) at colliders is primarily pursued via the detection of missing energy in particular final states. These searches are based on the production and decay processes where final states include DM particles and at least one Standard Model (SM) particle. DM will then reveal itself as missing energy. An alternative form to get a hint of a dark sector is via loop contribution to SM processes. In this case, it is not even relevant if the new particles have their origin in the dark sector of the model. In this work we discuss the impact of an arbitrary number of coloured scalars in single Higgs and double Higgs production at the Large Hadron Collider (LHC), and we show their complementarity. We determine the range of variation of the corrections relative to the SM for an arbitrary number of coloured scalars $n$, and discuss in more detail the cases $n=1$ and $n=2$.

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arXiv2023

Charged Higgs-Boson Decays into Quarks

We consider the full genuine next-to-leading order SUSY-QCD corrections to the charged Higgs decays into quarks supplemented by the NNLO corrections to the effective top and bottom Yukawa couplings. The NNLO corrections to the effective top Yukawa coupling are a new ingredient of our analysis. We arrive at an approximate NNLO prediction for MSSM charged Higgs decays after including the N$^4$LO QCD corrections for large charged Higgs masses. The residual uncertainties are in the percent range or below, depending on the particular MSSM scenario.

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arXiv2023

Electroweak Corrections to Higgs Boson Decays in a Complex Singlet Extension of the SM and their Phenomenological Impact

The complex singlet extension CxSM of the Standard Model (SM) is a simple extension of the SM with two visible Higgs bosons in the spectrum and a Dark Matter (DM) candidate. In this paper we complete the computation of the next-to-leading (NLO) electroweak (EW) corrections to on-shell and non-loop-induced Higgs decays. Our calculations are implemented in the code EWsHDECAY which also includes the relevant QCD corrections. Performing an extensive parameter scan in the model and including all relevant theoretical and experimental single- and di-Higgs as well as DM constraints, we obtain a viable parameter sample. We find that current DM constraints are able to test the model in DM mass regions where collider searches are not sensitive. The relative EW corrections turn out to be large for scenarios with relatively large couplings, threshold effects or small leading-order (LO) widths. Otherwise, they are of typical EW size and can amount up to about 20-25%. The theory uncertainty derived from the change of the renormalization scheme dependence then is of a few per cent. While the NLO corrections applied in the constraints due to single- and di-Higgs searches impact the validity of specific parameter points, the overall shape of the allowed parameter region is not yet sensitive to the EW corrections. This picture will change with further increased experimental precision in the future and necessitates precise predictions on the theory side as presented in this paper.

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arXiv2023

`CP in the Dark' and a Strong First-Order Electroweak Phase Transition

We investigate the potential of the model `CP in the Dark' for providing a strong first-order electroweak phase transition (SFOEWPT) by taking into account all relevant theoretical and experimental constraints. For the derivation of the strength of the phase transition we use the one-loop corrected, daisy-resummed effective potential at finite temperature, implemented in the C++ code BSMPT, to determine the global minimum at the critical temperature. The model `CP in the Dark' provides a dark matter (DM) candidate as well as explicit CP violation in the dark sector. We find a broad range of viable parameter points providing an SFOEWPT. They are within the reach of XENON1T and future invisible Higgs decay searches for DM. `CP in the Dark' also offers SFOEWPT points that feature spontaneous CP violation at finite temperature. Having not only an SFOEWPT that provides the necessary departure from thermal equilibrium, but also a source of additional non-standard CP violation, opens a promising gate towards enabling the generation of the baryon asymmetry of the universe (BAU) through electroweak baryogenesis.

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arXiv2022

The Trilinear Higgs Self-Couplings at ${\cal O}(α_t^2)$ in the CP-Violating NMSSM

In supersymmetric theories the Higgs boson masses are derived quantities where higher-order corrections have to be included in order to match the measured Higgs mass value at the precision of current experiments. Closely related through the Higgs potential are the Higgs self-interactions. In addition, the measurement of the trilinear Higgs self-coupling provides the first step towards the reconstruction of the Higgs potential and the experimental verification of the Higgs mechanism sui generis. In this paper, we advance our prediction of the trilinear Higgs self-couplings in the CP-violating Next-to-Minimal Supersymmetric extension of the SM (NMSSM). We provide the ${\cal O}(α_t^2)$ corrections in the gaugeless limit at vanishing external momenta. The higher-order corrections turn out to be larger than the corresponding mass corrections but show the expected perturbative convergence. The inclusion of the loop-corrected effective trilinear Higgs self-coupling in gluon fusion into Higgs pairs and the estimate of the theoretical uncertainty due to missing higher-order corrections indicate that the missing electroweak higher-order corrections may be significant.

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arXiv2022

Leptonic Anomalous Magnetic and Electric Dipole Moments in the CP-violating NMSSM with and without Inverse Seesaw Mechanism

The new results on the muon anomalous magnetic moment (AMM) published by Fermilab in 2021, did not lead to a reduction of its long-pending deviation from the Standard Model (SM) value by more than 4$σ$. The explanation of this discrepancy by adding new particles to the theory puts many new physics models under tension when combined with the null results of the LHC direct searches for new particles. In this paper, we investigate the CP-violating Next-to-Minimal Supersymmetric extension of the SM (NMSSM) with and without an inverse seesaw mechanism. We compute the one-loop supersymmetric contributions to the AMM and the two-loop Barr-Zee-type diagrams with effective Higgs couplings to photons for the leptonic electric dipole moments (EDMs). The effects of the extended (s)neutrino sector on the muon AMM and on the mass of the SM-like Higgs boson can be significant. Complex phases can have an important impact on the AMM. On the other hand, the stringent limits from the EDMs on the complex phases have to be taken into account. Our calculations have been implemented in the Fortran codes NMSSMCALC and NMSSMCALC-nuSS which are publicly available. Besides the leptonic AMMs and EDMs, these programs can compute the Higgs boson masses and mixings, together with Higgs boson decay widths and branching ratios taking into account the mostup-to-date higher-order corrections in the NMSSM with and without inverse seesaw mechanism.

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arXiv2022

Pseudoscalar MSSM Higgs Production at NLO SUSY--QCD

One of the most important mechanisms at the Large Hadron Collider (LHC) for the production of the pseudoscalar Higgs boson of the Minimal Supersymmetric Standard Model (MSSM) is the loop-induced gluon fusion process $gg\to A$. The higher-order QCD corrections have been obtained a long time ago and turned out to be large. However, the genuine supersymmetric (SUSY--)QCD corrections have been obtained only in the limit of large SUSY particle masses so far. We describe our calculation of the next-to-leading-order (NLO) SUSY--QCD results with full mass dependence and present numerical results for a few representative benchmark points. We also address the treatment of the effective top and bottom Yukawa couplings, in the case of heavy SUSY particles, in terms of effective low-energy theories where the heavy degrees of freedom have been decoupled. Furthermore, we include a discussion of the relation between the SUSY--QCD corrections that we have computed and the Adler--Bardeen theorem for the axial anomaly. In addition, we apply our results to the gluonic and photonic pseudoscalar Higgs decays $A\to gg,γγ$ at NLO.

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arXiv2022

Top-Yukawa-induced Corrections to Higgs Pair Production

Higgs-boson pair production at hadron colliders is dominantly mediated by the loop-induced gluon-fusion process $gg\to HH$ that is generated by heavy top loops within the Standard Model with a minor per-cent level contamination of bottom-loop contributions. The QCD corrections turn out to be large for this process. In this note, we derive the top-Yukawa-induced part of the electroweak corrections to this process and discuss their relation to an effective trilinear Higgs coupling with integrated out top-quark contributions.

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arXiv2022

Electroweak Phase Transition in a Dark Sector with CP Violation

In this paper, we investigate the possibility of a strong first-order electroweak phase transition (SFOEWPT) in the model `CP in the Dark'. The Higgs sector of the model consists of two scalar doublets and one scalar singlet with a specific discrete symmetry. After spontaneous symmetry breaking the model has a Standard-Model-like phenomenology and a hidden scalar sector with a viable Dark Matter candidate supplemented by explicit CP violation that solely occurs in the hidden sector. The model `CP in the Dark' has been implemented in the C++ code BSMPT v2.3 which performs a global minimisation of the finite-temperature one-loop corrected effective potential and searches for SFOEWPTs. An SFOEWPT is found to be allowed in a broad range of the parameter space. Furthermore, there are parameter scenarios where spontaneous CP violation is generated at finite temperature. The in addition spontaneously broken $\mathbb{Z}_2$ symmetry then leads to mixing between the dark and the visible sector so that CP violation in the dark is promoted at finite temperature to the visible sector and thereby provides additional sources of CP violation that are not restricted by the electric dipole moment measurements at zero temperature. Thus, `CP in the Dark' provides a promising candidate for the generation of the baryon asymmetry of the universe through electroweak baryogenesis.

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arXiv2022

Electroweak Corrections to Dark Matter Direct Detection in the Dark Singlet Phase of the N2HDM

Direct detection experiments are the only way to obtain indisputable evidence of the existence of dark matter (DM) in the form of a particle. These experiments have been used to probe many extensions of the Standard Model (SM) that provide DM candidates. Experimental results like the latest ones from XENON1T lead to severe constraints in the parameter space of many of the proposed models. In a simple extension of the SM, the addition of a complex singlet to the SM content, one-loop corrections need to be taken into account because the tree-level cross section is proportional to the DM velocity, and therefore negligible. In this work we study the case of a DM particle with origin in a singlet but in a larger framework of an extension by an extra doublet together with the extra singlet providing the DM candidate. We show that in the region of interest of the present and future direct detection experiments, electroweak corrections are quite stable with a $K$-factor very close to one.

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arXiv2022

Two Higgs doublets, Effective Interactions and a Strong First-Order Electroweak Phase Transition

It is well-known that type II two Higgs doublet models (2HDMs) can struggle to facilitate a strong first-order electroweak phase transition in the early universe whilst remaining theoretically appealing scenarios for many reasons. We analyse this apparent shortfall from the perspective of additional new physics. Starting from a consistent dimension-6 effective field theory Higgs potential extension, we identify the Higgs potential extensions that provide the necessary additional contributions required to achieve a strong first-order electroweak phase transition and trace their phenomenological implications for the Large Hadron Collider. In passing, we critically assess the reliability of the dimension-6 approximation depending on the expected 2HDM phenomenology. In particular, we focus on the role of Higgs pair production (resonant and non-resonant) and interference effects expected in top final states, which are the prime candidates of 2HDM exotics discoveries.

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arXiv2022

One-loop Corrections to the Higgs Boson Invisible Decay in a Complex Singlet Extension of the SM

The search for dark matter (DM) at colliders is founded on the idea of looking for something invisible. There are searches based on production and decay processes where DM may reveal itself as missing energy. If nothing is found, our best tool to constrain the parameter space of many extensions of the Standard Model (SM) with a DM candidate is the Higgs boson. As the measurements of the Higgs couplings become increasingly precise, higher-order corrections will start to play a major role. The tree-level contribution to the invisible decay width provides information about the portal coupling. Higher-order corrections also gives us access to other parameters from the dark sector of the Higgs potential that are not present in the tree-level amplitude. In this work we will focus on the complex singlet extension of the SM in the phase with a DM candidate. We calculate the one-loop electroweak corrections to the decay of the Higgs boson into two DM particles. We find that the corrections are stable and of the order of a few percent. The present measurement of the Higgs invisible branching ratio, BR$(H \to$ invisible $) < 0.11$, already constrains the parameter space of the model at leading order. We expect that by the end of the LHC the experimental measurement will require the inclusion of the electroweak corrections to the decay in order to match the experimental accuracy. Furthermore, the only competing process, which is direct detection, is shown to have a cross section below the neutrino floor.

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arXiv2021

Loop-corrected Higgs Masses in the NMSSM with Inverse Seesaw Mechanism

In this study, we work in the framework of the Next-to-Minimal extension of the Standard Model (NMSSM) extended by six singlet leptonic superfields. Through the mixing with the three doublet leptonic superfields, the non-zero tiny neutrino masses can be generated through the inverse seesaw mechanism. While $R$-parity is conserved in this model lepton number is explicitly violated. We quantify the impact of the extended neutrino sector on the NMSSM Higgs sector by computing the complete one-loop corrections with full momentum dependence to the Higgs boson masses in a mixed on-shell-$\overline{\mbox{DR}}$ renormalization scheme, with and without the inclusion of CP violation. The results are consistently combined with the dominant two-loop corrections at ${\cal O}(α_t(α_s+α_t))$ to improve the predictions for the Higgs mixing and the loop-corrected masses. In our numerical study we include the constraints from the Higgs data, the neutrino oscillation data, the charged lepton flavor-violating decays $l_i \to l_j + γ$, and the new physics constraints from the oblique parameters $S,T,U$. We present in this context the one-loop decay width for $l_i \to l_j + γ$. The loop-corrected Higgs boson masses are included in the Fortran code NMSSMCALC-nuSS.

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